Cultural Practices

Crop Budgets

Budgets are simply a formal means of organizing relevant economic information to help you make business decisions. Enterprise budgets that list all costs, income, and net returns for a single product are a fundamental planning and analysis tool.

The costs, income, and net returns on an enterprise budget are commonly shown for a full year, coinciding with the business reporting cycle. Enterprise budgets are especially helpful for evaluating the feasibility of an existing or potential crop, reviewing line items to identify potential savings or efficiencies, and for developing a crop’s cost of production and therefore target market price.  Additionally, vegetable enterprise budgets expressed on a per acre basis allow for comparisons across crops, between farms, and over several years.

Many websites offer a good starting point when developing crop enterprise budgets. Sites listing specific vegetable enterprise budgets include:

In addition to the above sites, the National Agricultural Risk & Farm Management Library has a budget library easily searched by commodity and geographic area. See https://agrisk.umn.edu/Budgets.

As a final note, when reviewing enterprise budgets developed elsewhere, it is important to identify the author's assumptions about the methods of production, levels of input use and market channels. These assumptions have a significant influence on income and cost estimates, meaning that these examples should only be used as examples. Enterprise budgets taken off the web should be modified and the numbers adjusted to fit your specific resources, practices and markets. For diversified vegetable and fruit operations, the thought of building enterprise budgets for each crop can be overwhelming. Start with few per year, prioritizing crops you grow in the largest quantities, ones that you question the profitability of, or crops that you are considering adding or dropping. 

For assistance with enterprise budget development and evaluation, contact your local Cooperative Extension office and/or USDA Service Center.

Plant Nutrients

This section briefly describes the major and minor nutrients required by all crop plants. The following section, Fundamentals of Soil Health and Soil Fertility Management, addresses the responsible application of fertilizers and soil amendments and stewardship of soils to economically and efficiently provide plant nutrients while minimizing losses and subsequent negative environmental effects. The third and fourth sections, Soil Testing and Fertilizers and Soil Amendments, describe soil testing methods and the many inputs commonly used to provide crop nutrient needs.

An element is considered essential to plant growth if it becomes part of plant tissue or is involved in metabolic functions and the plant cannot complete its lifecycle without it. There are 17 elements currently considered essential to plant growth. Listed in order of abundance in plant tissue, the 17 essential elements are: Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N), Potassium (K), Calcium (Ca), Magnesium (Mg), Phosphorus (P), Sulfur (S), Chlorine (Cl), Iron (Fe), Boron (B), Manganese (Mn), Zinc (Zn), Copper (Cu), Molybdenum (Mo), and Nickel (Ni). Plants obtain C, H, and O from air and water during photosynthesis. Together, these three elements make up approximately 95% of a plant's dry matter. Plants obtain the other 14 essential elements, called mineral nutrients, from soil. The mineral nutrients are classified as either macronutrients or micronutrients based on their relative abundance in plants. The six macronutrients, required in relatively large quantities, are N, P, K, S, Ca, and Mg. The eight micronutrients, required in relatively small quantities, are Cl, Fe, B, Mn, Zn, Cu, Ni, and Mo. Other nutrients, such as Silicon (Si), have shown to be beneficial in crop growth and disease suppression, but are not essential for the plant to complete its life cycle.

Nitrogen

Nitrogen is essential to nearly every aspect of plant growth, but it is one of the most difficult nutrients to manage. When plant available N exceeds crop demand, nitrate (NO3) accumulates in soil, increasing the risk of N loss to the environment. Excessive levels of available N can also produce succulent plants that are more susceptible to environmental stress and pest pressure. When plant-available N is too low, crop health and productivity suffer. Understanding of the forms of N in the soil and the factors that influence them will help improve management of this dynamic nutrient.

The Nitrogen Cycle

Practical knowledge of the N cycle is key to effective and efficient N management. The N cycle is extremely dynamic and its behavior in soil is complex. Nitrogen transformations and losses are affected by the form of N added, soil characteristics and conditions, and the vagaries of the weather. The rate and magnitude of N transformations and losses are difficult to accurately predict.

 

The nitrogen cycle

Figure 1. The Nitrogen Cycle

 

Nitrogen Inputs

As shown in Figure 1, there are two forms of the N used by plants: ammonium (NH4) and nitrate (NO3). In addition to commercial fertilizer sources, plant-available N in the soil may increase through mineralization (the microbial conversion of organic N to ammonium and then nitrate) of soil organic matter, manure and other organic residuals. See also Fertilizers and Soil Amendments

Nitrogen in soil organic matter: Organic matter contains the largest pool of soil N, usually comprising more than 90% of total soil N. The total amount of organic matter N in the plow layer of agricultural soils is impressively large. As a rule of thumb, you can assume that for each 1% of organic matter in the surface 6 inches of soil, there are 1000 lbs of N per acre. Thus, a soil with 3% organic matter contains about 3000 lbs of N per acre.

The amount of total organic matter N that becomes available to plants in any one year, is relatively small as a percentage of the total organic matter. For most soils, 2%-4% of the total organic matter N is mineralized, or converted to forms plants can use, annually. This is roughly equivalent to 20-40 lb of available N per acre for each 1% of organic matter in the surface 6 inches of soil. This mineralization is not constant throughout the growing season, however. A flush of available N is normally mineralized in late spring with lower rates of mineralization occurring during the growing season. Moisture conditions will greatly influence mineralization, with the highest rates when the soil is well-aerated and near water holding capacity. Small flushes of N will be released when dry soils are re-wetted during the season. The rate of mineralization is dependent on the activity of microbes, especially bacteria. Such activity is favored by warm, well-aerated soils with adequate, but not excessive, moisture and a pH above 6.0. These conditions are also favorable for the growth of most vegetables. Excessively wet conditions can greatly limit bacterial activity, and therefore N mineralization. For these reasons, the N contribution of mineralizing soil organic matter is frequently estimated at a conservative rate of 10 lb of available N per acre for each 1% of organic matter in the top 6 inches of soil.

Nitrogen found in manures and other waste products is discussed extensively in Fertilizers and Soil Amendments.

Previous crops: Many vegetables leave little residue in the field and thus they provide little N benefit to subsequent crops. However, previous forage or cover crops can supply large amounts of N to succeeding crops. Legumes, such as alfalfa and red clover, can furnish 100 lb or more of N to crops that follow (Table 1). Other legumes, mixed grass-legume stands and grass sods supply less N to succeeding crops. Keep in mind that most of the N is in the leaves, not the roots. If a legume hay crop is harvested, most of the N is removed from the field along with the hay.

Table 1: Nitrogen Credits from Previous Crops

Previous Crop

Nitrogen Credit
Lb N per acre

"Fair" clover (20%-60% stand)

40-60

"Good" clover (60%-100% stand)

60-90

"Fair" alfalfa (20%-60% stand)

60-90

"Good" alfalfa (60%-100% stand)

100-150

"Good" hairy vetch winter cover crop

120-150

Grass sod

20-40

Sweet corn stalks

30

 

Nitrogen Losses

Nitrogen losses occur in several ways. The loss of available soil N not only costs growers money, it has the potential to negatively impact both air and water quality. Understanding the cause of N losses can help growers make management decisions to improve N use efficiency and minimize negative environmental impact. 

Volatilization Losses: These losses occur mainly from surface applied manures and urea. The losses can be substantial; more than 30% of the N in topdressed urea can be volatilized if there is no rain or incorporation within two or three days of application. Losses are greatest on warm, breezy days. Volatilization losses tend to be greater from sandy soils and when pH values are above 7.0. Delaying the incorporation of manures after they are spread also leads to volatilization losses of N. Under the right conditions more than 50% of the ammonium N may be volatilized within the first 48 hours following surface application of manure without incorporation. 

Not only does volatilization reduce the fertilizer value of manure and urea, it can degrade air and water quality. Ammonia in the atmosphere can form particulates that contribute to smog. Ammonia emissions can also contribute to eutrophication of surface waters via atmospheric deposition.

Leaching Losses: The nitrate form of N is especially mobile in soil and is prone to leaching losses. Leaching losses are greatest on permeable, well-drained to excessively-drained soils underlain by sands or sands and gravel when water percolates through the soil. Percolation rates are generally highest when the soil surface is not frozen and evapotranspiration rates are low. Thus, October, November, early December, late March and April are times percolation rates are highest and leaching potential is greatest. This is why nitrate remaining in the soil after the harvest of annual crops such as corn in September is particularly susceptible to leaching. The use of fall cover crops can take up this residual N and prevent it from leaching. The N will then be released for crop use after the cover crop is plowed down in the spring. Of course, leaching can occur any time there is sufficient rainfall or irrigation to saturate the soil. This is why it is important to attempt to match fertilizer N application rates with crop N needs.  

Nitrate leaching accounts for the vast majority of N losses from cropland. Nitrate leaching can have a direct impact on water quality. When nitrate leaching contaminates groundwater serving drinking water supplies, human health can be impacted. The greatest concern is for infants; high levels of nitrate can be toxic to newborns, causing anoxia, also known as “blue-baby” syndrome. High nitrate levels in drinking water are also harmful to young or pregnant livestock. Depending on regional hydrology, leaching losses of nitrate can also contaminate surface waters.  

Denitrification Losses: These losses occur when nitrate is converted to gases such as nitrous oxide (N2O) and nitrogen gas (N2). The conversions occur when the soil becomes saturated with water. Poorly drained soils are particularly susceptible to such losses. In especially wet years on some soils, more than half the fertilizer N applied can be lost through denitrification. The most favorable conditions for denitrification occur in early spring and late fall. Minimizing the concentration of nitrate in the soil during these periods by delaying N application in the spring and planting cover crops in the fall will help reduce denitrification losses.

Most of the N lost during denitrification is in the form of the inert nitrogen gas (N2) which has no negative impact on the environment (our atmosphere is approximately 78% N2). Only a small percentage of denitrified N is lost as nitrous oxide (N2O); however, it is a powerful greenhouse gas. The impact of 1 lb of nitrous oxide on atmospheric warming is over 300 times greater than 1 lb of carbon dioxide. Agricultural activities account for over 70% of nitrous oxide emissions in the US. 

Immobilization: Immobilization occurs when soil microorganisms absorb plant-available forms of N. The N is not really lost from the soil because it is held in the bodies of the microorganisms. Eventually, this N will be converted back to plant-available forms. In the meantime, however, plants are deprived of this N, and N shortages in the plants may develop. Immobilization takes place when highly carbonaceous materials such as straw, sawdust or woodchips are incorporated into the soil. Manure with large amounts of bedding and compost with C:N ratios greater than 30:1 may cause some immobilization.

Crop Removal of Nitrogen: A significant quantity of N is removed from soil via crop harvest. For example, good sweet corn crops may remove over 150 lb N per acre annually. Anticipated crop removal of N is one of the factors used in making N fertilizer recommendations. Depending on the crop, variable amounts of the nitrogen taken up by the crop are returned to the soil after harvest in nonharvested plant parts. With sweet corn this can be as much as 100 lb N per acre. As these leaves and stalks decompose, the N is released into the soil for use by a subsequent crop. Cover crops can take up much of this N to prevent losses by leaching or denitrification.

Nitrogen Management

Topdressing and Sidedressing Nitrogen

Topdressing is defined as a fertilizer application to a crop any time after planting. In popular usage, topdressing sometimes refers to a broadcast application of fertilizer made after planting. Alternatively, fertilizer can be sidedressed as a band along the side of the row of a growing crop. Sidedressing is commonly done immediately before or during cultivation. When urea-containing fertilizers are used, cultivation helps reduce volatilization losses.

Sidedressing of relatively soluble N fertilizer is an important component of efficient nitrogen management. The N accumulation pattern for annual crops is very similar to biomass accumulation (Figure 2). Early in the season, when crop growth is slow, crop N needs are very small. A starter fertilizer is generally sufficient to satisfy those needs. Any soil nitrate in excess of crop N needs during this period is prone to leaching and/or denitrification losses. The next phase of crop development is characterized by rapid vegetative growth. The N demand during this phase is the highest of the growing season. As much as 85% of the total N uptake occurs during this period. Efficient recovery of the fertilizer portion of N can be achieved by sidedressing fertilizer N immediately before this phase. Delaying application of a large portion of N fertilizer until sidedress also allows growers to use the Pre-sidedress Soil Nitrate Test (PSNT) to help determine N needs.

Figure 2. Generalized nitrogen accumulation curve for annual crops

Pre-sidedress Soil Nitrate Test (PSNT)

The dynamic nature of the N cycle and its sensitivity to weather limits the value of routine, pre-season soil testing for predicting N availability during the season in our humid environment. However, under certain circumstances, in-season soil testing has proven useful. The PSNT, developed by Dr. Fred Magdoff at the University of Vermont in the early 1980’s, was originally intended to help estimate the amount of available N for field corn in fields where manure had been applied and/or forage legumes were grown in rotation. Over the last thirty years, research conducted in the Northeast has found the PSNT useful for improving N management of several vegetable crops including sweet corn, peppers, pumpkin, winter squash, and cabbage. The PSNT is most suitable for use with annual crops, which accumulate N rapidly within a single growing season.

The PSNT is especially useful where large amounts of N from mineralization are expected, and the test works best when pre-plant and starter fertilizer N rates are less than about 50 lbs N per acre. PSNT samples are collected about a week before the rapid growth phase (see Figure 2), to provide an indication of how much N has been made available from mineralization. During wet springs with heavy leaching rains, or in sandy soils with rapid losses, the PSNT will also provide some indication of how much N remains in the root zone.

As with all soil testing, information from a PSNT should be used along with the grower’s experience and knowledge of the field. Interpretation of the PSNT is also crop-specific. Research in the Northeast has shown that when the soil nitrate N level is above 20-25 ppm there is rarely an economic response to the application of sidedress fertilizer N for sweet corn. Based on research and experience in New England, New Jersey, and New York, a threshold of 25-30 ppm seems appropriate for peppers, tomatoes, butternut squash, cabbage, pumpkin, and probably other long-season vegetable crops. When PSNT values are below threshold levels, the appropriate rate of sidedress N should be determined based on the level of nitrate N reported, previous N application, realistic yield expectation, the field’s management history, and growing season conditions. See Table 2 for recommendations on timing of sampling and making sidedressing applications of N based on PSNT for many vegetable crops. 

Table 2. Timing of PSNT and sidedress nitrogen needs of crops1

CROP SOIL SAMPLING TIME FOR PSNT SIDEDRESS lbs n per ACRE2
Beets After thinning (2-4 leaves) 30
Cabbage, brussels sprouts, broccoli 2 weeks after transplanting 60
Cauliflower 2 weeks after transplanting 30
Celery 2 weeks after transplanting, again 3-4 weeks later 40 twice, 3-4 weeks apart
Cucumber, muskmelon Before vines are 6" long 40
Eggplant 3-4 weeks after planting, again 3-4 weeks later 30-50
Lettuce, endive, escarole 2 weeks after transplanting or after thinning (2-4 leaves) 30-50
Pepper 3-4 weeks after planting, again 3-4 weeks later 50, and 40 later at fruit set
Spinach 2-4 leaves, again after first cutting 30
Sweet corn when plants are 6-10" tall 60-90
Tomato 3-4 weeks after planting, again 3-4 weeks later 30 twice, 3-4 weeks apart

1 Adapted from: Rutgers Cooperative Extension Bulletin by J. Heckman, “Soil Nitrate Testing as a Guide to Nitrogen Management for Vegetable Crops”

2 If soils have 0-30 ppm nitrate, apply the full sidedress amount recommended. For sweet corn, the threshold is 25 ppm nitrate. Above 30 ppm no additional N is needed and could hurt yields.

Samples for the PSNT should consist of a well-mixed composite of 10-20 cores or slices of soil to a depth of 12 inches. This is a deeper sample than what is recommended for routine soil sampling. A deeper sample is required for nitrate testing to accurately reflect the concentration in the effective root zone due to its mobility in soil. Avoid sampling fertilizer bands or areas that may have received extra N. About one cup of the composite should be dried to stabilize the nitrate. A good method is to spread a thin layer of the soil on a cookie sheet or aluminum foil to air dry. Use a fan to reduce drying time. Do not place damp samples on absorbent material because it can absorb some of the nitrate. You can skip the drying step if you can deliver the samples to the soil testing lab in less than 24 hours; however, samples should be kept cool. Fields should be sampled for the PSNT about a week before the time when sidedressing is normally done. This should allow adequate time for drying, shipping, and testing (turnaround time in the lab is about 24 hours) and for you to plan your fertilizer program.

Phosphorus

For the purposes of fertilizer grades and recommendations, phosphorus (P) is measured as phosphate, or P2O5

The amount of extractable P in a soil should not exceed the optimum soil test range to obtain the most economic return from P applications and to avoid negatively impacting water quality.  When extractable P exceeds the environmental critical concentration, which is much higher than the soil test optimum range, the risk of dissolved P loss in subsurface water flow or runoff is significantly increased. This P pollution can stimulate excessive growth of algae in lakes and ponds. When the algae die and their biomass is rapidly decomposed by microorganisms, oxygen levels are reduced below the level needed by fish and shellfish, resulting in large die-offs of aquatic life.

Excessive P amounts in soils are difficult to reduce because vegetable crops remove little P from the soil compared to N or K. For example, Table 4 shows that sweet corn takes up about 155 lb N per acre and about 105 lb K per acre, but only about 20 lb P per acre. However, many growers apply about 100 lb P per acre annually. This is justified only if soil test P levels are below optimum. If the soil test level for P is above optimum, there is little if any crop response to additional P applications.

Plant uptake of P is extremely slow in cold soils. For this reason, when planting early into soils testing Optimum or lower, it is often advisable to apply up to 30 pounds of P2O5 as starter fertilizer in a band about 2" below and 2" to the side of the seed when planting, or as a liquid around transplants. Keep in mind that P availability is reduced in alkaline soils (pH >7.3) as it will bind with Ca, and in acidic soils (pH <5.5) when it binds with Al, in both cases becoming unavailable to plants.  Therefore, it is important to first balance the soil’s pH with lime applications into the range of pH 6-7 before making P2O5 applications.

Potassium

Potassium (K) is measured as potash (K2O), similar to the way P is measured as P2O5. Crop need for K varies considerably as can be seen in Table 4. It is important that the soil K plus the applied K is enough to meet crop needs. However, excessive levels should be avoided because K can interfere with the uptake of Ca and Mg (see Cation Exchange Capacity and Base Saturation under Fundamentals of Soil Health and Soil Fertility). K is subject to leaching on sandy soils low in organic matter, so if high amounts are needed, split applications should be used.  Very high application rates of K are also known to suppress Mg uptake, and when soil test Mg levels are low, may cause Mg deficiency.

Calcium

Calcium (Ca) is usually supplied in sufficient quantities by liming if appropriate liming materials are chosen (see Soil Acidity, pH, and Liming). If soil pH is high and Ca is needed, it can be supplied without affecting pH by applying calcium sulfate (gypsum) which contains 19%-23% Ca. Small amounts can also be applied as calcium nitrate fertilizer (19% Ca) or superphosphate (18%-21% Ca). See Table 5.

Magnesium

Magnesium (Mg) is most economically applied as dolomitic or high-mag limestone (see Soil Acidity, pH, and Liming). If liming is not needed, Sul-Po-Mag (11% Mg, 22% K) can be used. Blended fertilizer containing Mg can also be ordered.

Micronutrients

Micronutrient deficiencies are rarely observed in New England soils, especially on soils that have a history of compost or manure applications. For this reason little research has been done to calibrate soil tests for micronutrients, and there are no reliable soil test calibration data to interpret soil micronutrient levels and make recommendations for amounts of micronutrients to apply. Most New England labs offer micronutrient soil testing and present results relative to values typically observed in soils analyzed in their laboratory for comparison.

Calibration data for plant tissue analysis are also limited. When a grower suspects a micronutrient deficiency, the recommended procedure is to collect soil and plant tissue samples from areas in the field with good and poor plant growth, and have the samples analyzed using standard methods. A relative comparison of the concentrations of micronutrient in the soil and plant tissue samples will usually allow a diagnosis to be made. Foliar applications of micronutrients may alleviate nutrient deficiencies observed during the season. However, applications of micronutrients to the soil are the better long-term approach to address the rare occurrence of micronutrient deficiencies. 

Micronutrient deficiencies are most likely to occur in sandy soils with low organic matter. High soil pH may also bring about micronutrient deficiencies, especially in sandy soils. It may be necessary to maintain pH between 6 and 6.5 to avoid problems in coarse-textured soils with low organic matter. Of all the micronutrients, boron (B) is most likely to be needed in New England to supplement soil levels for vegetable production. Cauliflower, broccoli, cabbage and beets are most susceptible to “hollow heart” caused by boron deficiency. Boron, copper, zinc and molybdenum have small ranges for optimum soil test values, which means the difference between deficient levels and toxic levels in the soil are small. Be careful with applications of these nutrients to avoid toxic quantities. Some vegetable crops are particularly sensitive to high levels of boron. Sensitive crops should not be planted on fields following crops that have received boron application. Table 3 lists crops according to their sensitivity to boron.

Table 3: Relative Tolerance of Vegetables to Boron

Tolerant Semitolerant Sensitive
artichoke
asparagus
beet
broad bean
carrot
parsley
spinach
tomato
bell pepper
broccoli
cabbage
cauliflower
celery
corn
lettuce
muskmelon
pea
potato
pumpkin
radish
sunflower
sweet potato
turnip
bean
cucumber
garlic
Jerusalem artichoke
lima bean
pea

Adapted from L.V. Wilcox, Determining the quality of irrigation water, USDA Agricultural Information Bulletin 197 (1958) and information from Robert Becker, Cornell University.

Fundamentals of Soil Health and Fertility

Soil health (or soil quality) has been defined as the capacity of a soil to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation over a human time scale (thousands of years). Similar but distinct from soil health, soil fertility can be viewed as a function of the biological, physical and chemical characteristics of soil that supply plant nutrient requirements. 

Holistically, a healthy and fertile soil must have: good structure and drainage, sufficient depth for root growth, sufficient (but not excessive) nutrient availability, small weed, insect pest, and plant pathogen populations, large populations of beneficial organisms (including microbes), no toxins, and resilience to adverse conditions. 

Soil Health

A number of individual soil tests may be used to assess aspects of soil health, including those obtained with routine soil analysis. However, a comprehensive evaluation includes a suite of complementary tests to measure chemical, physical, and biological soil properties. Researchers at Cornell University evaluated a large number of these measurements for use in Northeastern cropping systems and now offer the most meaningful measurements as part of the Cornell University Soil Health Test. This suite of soil health indicators is designed to provide growers with helpful information about problems that may limit crop productivity and/or soil performance. Recommendations are provided with the results to help growers address problems that may be identified. More information about the Cornell University Soil Health Test (including sampling protocol, current prices, and submission forms) can be found at http://soilhealth.cals.cornell.edu/. Other soil testing laboratories in New England now offer soil health tests as well; check with your local lab.

Soil Organic Matter

Soil organic matter (SOM) is critical for soil health because of the beneficial chemical, physical and biological properties it imparts. SOM increases soil nutrient availability, being a source of nutrients itself as well as by increasing cation exchange capacity. SOM also benefits the physical properties of soil by contributing to soil structure and increasing water holding capacity. Finally, SOM supports soil biology as a substrate for the growth of soil microbial communities. In turn, these soil microbes mineralize SOM into plant-available nutrients, develop symbiotic mycorrhizal relationships between soil fungi and plant roots, and produce sticky substances responsible for binding soil aggregates.

SOM is composed of materials containing carbon that came from living organisms, including plant and animal residues, organic-based amendments, and soil bacteria and fungi, all in various stages of decomposition. SOM is often divided into two categories. The more stable component is humus, which is primarily comprised of long-dead material that is highly decomposed and beneficial for soil structure and carbon storage. Active SOM, on the other hand, is relatively undecomposed and accessible to soil microbes for mineralization. It is important to maintain both types of SOM (see Building Soil Organic Matter). In any case, it is important to maintain SOM because it is typically the most important component of soil for nutrient supply, water holding capacity, cation exchange capacity, and soil structure. 

Native total SOM content in soils used for vegetable production in New England is almost always less than 10% and typically in the 2-6% range. SOM accumulation is generally limited by several abiotic factors, including temperature, moisture, and soil texture. Well-drained, coarsely textured soils tend to have lower levels of SOM, due in part to the rapid microbial decomposition rates favored by these soil conditions. In contrast, loamy soils often have 3-6% SOM. 

SOM supplies nutrients through the process of mineralization, which is the microbial decomposition of organic compounds into carbon dioxide and their mineral constituents. Soil microbes are most active in warm soils (over 70°F) that are moist, well-aerated, and have a pH between 6 and 7 (also ideal conditions for most vegetable crops). Mineralization of nutrients will proceed rapidly under these conditions, provided there is an adequate supply of SOM and an abundant soil microbial community.

SOM directly influences water holding capacity through its capacity to absorb large amounts of water. It also indirectly boosts water holding capacity by improving soil structure, creating more pore space for water storage and larger pores for air. Soil structure is enhanced by SOM because, as it decomposes, sticky compounds like gums, carbohydrates, and resins are produced by microorganisms. These gums bind soil particles together into secondary aggregates. This in turn bolsters cation exchange capacity, which is influenced by both clay and SOM content (both supply negatively charged sites that hold cations). In most New England soils, the stable humus portion of SOM accounts for the vast majority of the cation exchange capacity, as these soils are typically low in clay content. See also Cation Exchange Capacity and Base Saturation

Building Soil Organic Matter

Soil organic matter (SOM) is in a constant state of flux, with additions and losses simultaneously occurring. To maintain SOM levels, one must ensure that losses do not exceed additions. 

SOM can be lost from soil through both wind and water erosion. However, the primary mechanism for SOM loss is microbial decomposition. Soil microbes use SOM as a source of energy and nutrition, converting SOM into carbon dioxide and its constituent mineral elements. The rate of SOM decomposition is controlled by a number of factors including soil temperature, moisture, aeration (oxygen), and the quality or characteristics of the SOM. In agricultural soils, these factors are all greatly influenced by soil management. For example, aggressive tillage and cultivation increases aeration and break apart soil aggregates that protect SOM from microbial decomposition. Reducing tillage and cultivation is an effective management strategy to maintain, or even increase, SOM content  (see Reduced Tillage).

There are a number of ways to increase or maintain SOM. Increasing the quantity of plant residues returned to the soil is one of the most sustainable methods strategies for maintaining SOM. Most vegetables leave little residue in the field, and SOM will usually decrease if these are the only residues provided to the system.  Although cover crops can add enough biomass to maintain SOM, it can be difficult to increase SOM with some cover crop species or mixes. Including sod-forming crops in the rotation, however, can increase SOM. A more rapid and direct method of increasing SOM is by adding organic amendments, like organic mulches and compost. While the application of organic amendments can rapidly increase SOM, extractable soil phosphorous (P) concentrations must be monitored to avoid excessive applications (see Fertilizers and Soil Amendments).

Cation Exchange Capacity and Base Saturation

Cation exchange capacity (CEC) is a measure of the soil’s ability to retain and supply nutrients, specifically the positively charged nutrients called cations. These include calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+), and many of the micronutrients. Cations are attracted to negatively charged surfaces of clay and organic particles called colloids. CEC is reported as milli-equivalents per 100 grams of soil (meq/100g) or as centimoles of charge per kilogram (cmole+/kg). CEC can range from below 5 meq/100g in sandy soils low in organic matter to over 20 meq/100g in finer textured soils and those high in organic matter. Low CEC soils are more susceptible to cation nutrient loss through leaching, and may not be able to hold enough nutrient cations for a whole season of crop production.

The cations Ca++, Mg++, K+, hydrogen (H+) and aluminum (Al+++) account for the vast majority of cations adsorbed on the soil colloids in New England soils. It is important to note that H+ and Al+++ are not plant nutrients. Both H+ and Al+++ are considered acidic cations because they tend to lower soil pH while Ca++, Mg++, and K+ are considered basic cations and have little to no influence on soil pH. If all the cations are basic and none are acidic, there would be a 100% base saturation and the soil pH would be close to 7 or neutral. In acid soils there are acidic cations adsorbed on the soil colloids (called exchangeable acidity) and the percent base saturation is less than 100. A soil with a pH between 6.5 and 6.8 will typically have a base saturation of 80%-90%.

Soil Acidity, pH, and Liming

One of the most important aspects of nutrient management is maintaining proper soil pH, a measure of soil acidity. A pH of 7.0 is neutral, less than 7.0 is acidic, and greater than 7.0 is alkaline. Most New England soils are naturally acidic and need to be limed periodically to keep the pH in the range of 6.5 to 6.8 for most vegetable crops. Scab-susceptible potato varieties are an exception, but some lime may still be needed to maintain the recommended pH of 5.0-5.2. When the soil is acidic, the plant availability of nitrogen (N), phosphorus (P), and potassium (K) is reduced and there are usually low amounts of calcium (Ca) and magnesium (Mg) in the soil. In contrast, most micronutrients are more soluble and are therefore more available to plants. Under very acidic conditions aluminum (Al), iron (Fe), and manganese (Mn) may be so soluble they can reach toxic levels. Soil acidity also influences soil microbes, which decompose organic matter and recycle crop nutrients. For example, when soil pH is low (below 6.0), bacterial activity is reduced and fungal activity increases. Acidic soil conditions also reduce the effectiveness of some pesticides. These conditions also limit the ability of cover crops like legumes to fix nitrogen. 

The most effective way to manage soil acidity is to apply agricultural limestone. The quantity of lime required is determined by the target pH (based on crops to be grown) and the soil's buffering capacity, measured in a soil test. Buffering capacity refers to the soil’s tendency to resist change in pH. Soil pH is only a measure of active acidity, the concentration of hydrogen ions (H+) in soil solution. When lime is added to a soil, active acidity is neutralized by chemical reactions that remove hydrogen ions from the soil solution. However, there are also acidic cations (H+ and Al+) adsorbed on soil colloids (see CEC, previous section) that can be released into the soil solution to replace those neutralized by the lime. This is called reserve acidity. Clays and soils high in organic matter have the potential for large amounts of reserve acidity. These soils are said to be well-buffered. To effectively raise the soil pH, both active and reserve acidity must be neutralized. Soil test labs determine buffering capacity and lime requirement by measuring or estimating the reserve acidity. 

The neutralizing power of lime is determined by its calcium carbonate equivalence. Suppliers can tell you the calcium carbonate equivalence of the lime you are purchasing. Recommendations are based on an assumed calcium carbonate equivalence of 100. If your lime is lower than 100, you will need to apply more than the recommended amount, and if it is higher, you will need less. To determine the amount of lime to apply, divide the recommended amount by the percent calcium carbonate equivalence of your lime and multiply by 100. Wood ash is another amendment that may be used to manage soil acidity. The calcium carbonate equivalence of wood ash is typically between 30-50%, but it can vary widely. If purchasing wood ash from a supplier, they will provide a recent analysis. Otherwise, the wood ash should be submitted to a lab offering lime analysis to determine the calcium carbonate equivalence.

The speed with which lime reacts in the soil is dependent on particle size and distribution in the soil. To determine fineness, lime particles are passed through sieves of various mesh sizes. A U.S. Standard 10-mesh sieve has 100 openings per square inch while a 100-mesh sieve has 10,000 openings per square inch. Lime particles that pass through a 100-mesh sieve are very fine and will dissolve and react rapidly (within a few weeks). Coarser material in the 20-30-mesh range will react over a longer period, one to two years or more. Agricultural ground limestone contains both coarse and fine particles. About half of a typical ground limestone consists of particles fine enough to react within a few months, but to be certain you should obtain a physical analysis from your supplier. Super fine or pulverized lime is sometimes used for a “quick fix” because all of the particles are fine enough to react rapidly.

Lime will react most rapidly if it is thoroughly incorporated to achieve intimate contact with soil particles. This is best accomplished when lime is applied to a fairly dry soil and disked in (preferably twice). When spread on a damp soil, lime tends to cake up and doesn’t mix well. A moldboard plow has little mixing action, therefore, disking is preferred. If growing vegetables in no-till fields, it is common to apply needed lime and work it in before limiting tillage in the field, then to apply a smaller amount of lime more frequently to the surface to maintain adequate pH. Lime moves slowly through the soil profile without incorportation. If lime is applied and not incorporated the material likley won’t be spread throughout the entire rootzone, reducing the neutralizing ability.  

Besides neutralizing acidity and raising soil pH, lime is also an important source of Ca and Mg for crop nutrition. It is important to select liming materials based on Ca and Mg soil content with the aim of achieving sufficient levels of each for crop nutrition. If the Mg level is low, a dolomitic lime (high magnesium lime) should be used; if Ca is below optimum, a calcitic (low-Mg lime) should be used.
 

Nutrient Recommendations

Normally it is not necessary to supply all the nutrient needs of a crop from fertilizer alone, because the soil already contains some quantity of nutrient elements available for crop growth. It is necessary to test the soil to determine its nutrient status, because only then can you determine the additional amounts of appropriate fertilizer materials to apply. Frequently, growers apply more fertilizer than the crop can use and the excess, especially nitrogen, is leached from the root zone into groundwater. 

The "Plant Nutrient Recommendations" tables in each crop section can be used to determine nutrient needs based on soil test results. Read the section on Soil Testing to better understand nutrient recommendations.

In general, the goal should be to maintain nutrient elements within the optimum range as reported on the soil test. When nutrient levels are within this range, the needs of most crops will be met. If levels are below optimum (low or medium), most crops would benefit by adding the appropriate nutrient(s) to increase levels to optimum. However, if levels are at above optimum (very high) levels, there will be no additional benefit and excess levels may reduce crop yield or quality and may cause environmental harm. This happens in fields where soil testing was not used to monitor fertility levels or when nutrients are applied even when soil levels are sufficient. When a nutrient is above optimum levels it should not be included in any amendments until the excess is taken up by crops. In this case, it is wise to temporarily stop applying compost or manures until nutrient levels are in the desired range because the addition of these amendments can add high levels of nutrients, especially phosphorus. This is a practical way to manage nutrient levels if small to moderate amounts of mixed crops are to be grown.

If a significant acreage of a particular crop is to be grown, fertilizers should generally be tailored to the specific needs of that crop, based on the amounts of nutrients that the crop is expected to remove during the growing season (see Table 4). If the soil tests indicate that a nutrient is optimum/high it is likely that the soil will supply enough to meet the crop's needs. However, many growers will apply enough of the nutrient to replace what is removed by the crop. If the test level is above optimum/very high, additional applications should normally be avoided unless the crop has an unusually high demand for a specific nutrient. Occasionally, nutrient applications may exceed the soil test recommendation or the expected average removed by the crop (Table 4) because a particular cultivar is considered a heavy feeder, such as long season Russet potatoes. Or, for example, a large crop of tomatoes can be expected to remove a large amount of potassium and it may be justified to apply some of this nutrient even if the soil test indicates a level somewhat above optimum. The nutrient recommendation tables for each crop have been developed on this basis of expected crop removal. This can also be a practical way to determine nutrient needs of high value crops, even when they are grown on a small scale. It is important to keep in mind that many factors can limit crop yield potential, and that simply adding more nutrients will not address any issues beyond nutrient deficiency.
 

Removal of Nutrients from the Soil

Table 4 lists amounts of certain nutrient elements that are removed by vegetable crops. It includes both the amounts removed by harvest and those that remain in crop residue and are returned to the soil. These figures for crop removal should be considered approximate. They can be used as a basis for adjusting your own application rates up or down on a trial basis. Keep in mind that nutrient removal varies with factors such as soil moisture, temperature, and pH. Plants can absorb large amounts of a nutrient if it is in abundance; but this may not increase yield. Excess levels of some nutrients can reduce the yield and/or quality of some crops.

Nutrients that are relatively immobile in the soil, such as phosphorus, calcium, magnesium and the micronutrients, are not all extracted by plants because the roots do not come in contact with all of the nutrients. This is especially true of certain vegetables that have small or sparse root systems. Most of the phosphorous applied to the soil becomes fixed in a form unavailable to plants. Thus, it is necessary to provide some excess amounts of nutrients when soil test levels are below the optimum range, and this is why rates sufficient to replace the amount removed by crops are sometimes recommended for soils that test in the optimum range.

Table 4: Approximate Nutrient Removal by Selected Vegetable Crops. 

Vegetable

 

Yield per acre1

Nutrient removal, lbs/acre

N

P2O5

K2O

Ca

Mg

Snap beans

Total

250 bu

30

20

35

7

3

Broccoli

heads

5 tons

20

2

45

 

 

 

other

 

145

8

165

 

 

 

Total

 

 

 

 

 

 

Cabbage

Total

20 tons

125

30

130

28

10

Carrots

roots

25 tons

80

20

200

 

 

 

tops

 

65

5

145

 

 

 

Total

 

145

25

345

 

 

Cauliflower

 

6 tons

45

18

43

4

3

Celery

tops

50 tons

170

 

380

 

 

 

roots

 

25

 

55

 

 

 

Total

 

195

80

435

110

27

Cucumbers

 

24 tons

100-200

33-72

100-400

 

 

Eggplant

 

16 tons

207

46

34

 

 

Kale

 

10 tons

125

30

110

50

10

Lettuce

 

15 tons

75

35

150

13

5

Muskmelons

fruit

11 tons

95

17

120

 

 

 

vines

 

60

8

30

 

 

 

Total

 

155

25

150

 

 

Onions

bulbs

20 tons

110

20

110

12

14

 

tops

 

35

5

45

 

 

 

Total

 

145

25

155

 

 

Peppers

fruits

12 tons

137

52

217

 

 

Potatoes, White

tubers

300 cwt

90

45

160

 

 

 

vines

 

60

20

60

 

 

 

Total

 

150

65

220

 

 

Potatoes, Sweet

roots

15 tons

75

55

160

 

 

 

vines

 

35

5

280

 

 

 

Total

 

110

60

440

10

15

Spinach

 

10 tons

100

25

100

24

10

Squash, Summer

 

10 tons

32

12

56

 

 

Squash, Winter

 

6 tons

12

10

58

 

 

Sweet Corn

ears

250 cr.

55

8

30

 

 

 

stalks

 

100

12

75

 

 

 

Total

 

155

20

105

 

 

Tomatoes

  fruit

30 tons

110

48

180

15

15

 

  vines

 

90

30

100

24

21

 

Total

 

200

78

280

39

36

1 These are assumed yields. Actual yields may vary depending on weather and cultural practices. Adjust nutrient removal rates accordingly. To convert to volume or count yield units see Table 15: Approximate Yields (page 37).

 

Nutrient Management Regulations

Several states in New England have nutrient management regulations that impact vegetable production practices. The EPA began regulating municipal waste water treatment facilities to manage water pollution, and more recently, regulations have gone in place to regulate non-point source pollution such as that coming from fertilizer or manure applications on agricultural fields. Below is a list of states with regulations and recommendations on how to comply.

Maine: Regulations for crop farms require the development of a nutrient management plan (NMP) if a farm is importing more than 100 tons of manure or regulated residuals annually. The nutrient management plan must address storage and utilization of manure and off-farm nutrients on land to which the regulated residuals or manure are applied. The NMP must include or provide for minimum distances between manure storage, stacking and spreading areas and property lines and surface water based on site-specific factors determined to be effective for controlling runoff and for preventing contamination of surface water. The NMP must include soil test reports for each field where manure or other crop nutrients will be applied, and soils must be tested for each field at least every 5 years. For each field, the NMP must show the calculation of nutrients required to grow the specific crop. The producer may write his/her own plan, but it must be approved by a Maine certified nutrient management planner licensed through the Nutrient Management Office. To find a licensed nutrient management planner, contact:

Mark F. Hedrich, Nutrient Management Program Manager. Maine Department of Agriculture, Conservation and Forestry, Division of Animal & Plant Health, 28 State House Station, Augusta, Maine 04333; 207-287-7608; mark.hedrich@maine.gov

New Hampshire: Best Management Practices (BMPs) for Agriculture are prepared by the Agricultural Best Management Practices Task Force and the USDA Natural Resources Conservation Service (NRCS) in Durham, NH and provides a guide for growers for handling manure, agricultural compost and chemical fertilizer. There is not a law that explicitly requires growers to follow them; however, it is in the producers’ best interest to follow these BMPs as they provide protection from nuisance allegations. State law under RSA 431:35 requires the New Hampshire Department of Agriculture, Markets & Food to respond to complaints involving the mismanagement of manure, agricultural compost and chemical fertilizer. Copies of the BMP manual are available to producers as a tool, but the NH Department of Agriculture, Markets & Food does not have the authority to enforce the implementation. A copy of the manual can be found here: http://agriculture.nh.gov/divisions/regulatory-services/nutrient-management.htm

Vermont: All farms must comply with the Required Agricultural Practices (RAPs) effective since July, 2017. The RAPs are practices and management strategies to which all types of farms must be managed to reduce the impact of agricultural activities to water quality. These standards are intended to improve the quality of Vermont’s waters by reducing and eliminating cropland erosion, sediment losses, and nutrient losses through improved farm management techniques, technical and compliance assistance, and where appropriate, enforcement. The RAPs establish nutrient, manure, and waste storage standards, make recommendations for soil health and establish requirements for vegetated buffer zones and livestock exclusion from surface water. The RAPs also establish standards for nutrient management planning and soil conservation. Full text of the RAPs regulations may be found on the Vermont Agency of Agriculture, Food and Markets here: https://agriculture.vermont.gov/rap. Questions regarding these regulations should be directed to the Vermont Agency of Agriculture, Food and Markets, Water Quality Division, AGR.WaterQuality@Vermont.gov, (802) 828-2431. A factsheet specific to the RAP applicability to vegetable producers can be found here: https://agriculture.vermont.gov/sites/agriculture/files/documents/VeggieFactsheet.pdf

Massachusetts: In 2012, the Massachusetts Legislature passed Chapter 262, An Act Relative to the Regulation of Plant Nutrients. The text of the enabling legislation can be found at: https://malegislature.gov/Laws/SessionLaws/Acts/2012/Chapter262. The Act requires the Department of Agricultural Resources (MDAR) to promulgate state-wide regulations to ensure that plant nutrients are applied in an effective manner to provide sufficient nutrients for plant growth while minimizing the impacts of the nutrients on water resources in order to protect human health and the environment. The Act also requires that these regulations are consistent with UMass Extension’s educational and outreach materials relative to nutrient management and fertilizer, which may be found here: https://ag.umass.edu/resources/agriculture-resources/umass-extension-nutrient-management. In response to the Act, MDAR developed regulations entitled “330 CMR 31.00: Plant Nutrient Application Requirements for Agricultural Land and Land Not Used for Agricultural Purposes”, found here: https://www.mass.gov/service-details/plant-nutrient-management. A detailed factsheet specific to nutrient regulations on agricultural land can found here https://www.mass.gov/doc/plant-nutrient-regulations-fact-sheet-for-agricultural-land/download. The regulation gives MDAR state-wide authority to regulate and enforce the registration and application of plant nutrients including, but not limited to, fertilizer, manure and micronutrients.  The Cape Cod Commission, Martha’s Vineyard Commission, and Nantucket Commission have the option to adopt their own ordinances in regard to nutrients and fertilizers, but they cannot be less restrictive than the state regulation.

Connecticut:  Currently there are no nutrient management regulations affecting vegetable farmers in CT. There is a Phosphorous Law (CT PA-1255) but it primarily affects wastewater treatment facilities and homeowners who may only apply P if a soil test shows a need and not during winter months.

Rhode Island: No regulations of nutrient applications are in place in RI, however, on a case by case basis (and rarely at that) regulation may occur as part of a response to an environmental violation, for example, a consent agreement resulting from water quality impairment.

Soil Testing

Routine soil analysis is the most accurate way to determine lime and fertilizer needs. The shotgun approach to nutrient management, applying all nutrients annually whether needed or not, is neither practical nor economical. Vegetable growers must know the nutrient status of the soil and then match application rates to crop needs. This is important to achieve optimum yield and quality, to maximize return on investment, and to limit nutrient losses to the environment.

Soil Test Methods

Soil test methods used for vegetable production are designed to provide a measurement of soil pH and nutrient availability. Soil testing labs use different methods, and it is best to select a lab using analytical methods appropriate for New England soils that provide soil test interpretations based on field correlation and calibration under local conditions. A list of New England soil test laboratories is provided at the end of this section. In New England, routine soil analysis typically includes a measure of extractable phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S), plus several of the micronutrients (e.g., boron, manganese, zinc, copper, and iron). In addition to routine soil analysis, other tests and analytical services are available including: soil organic matter, soluble salts (conductivity), Pre-sidedress Soil Nitrate Test (PSNT), plant tissue analysis, manure and compost analysis, and irrigation water testing.

Several labs have recently adopted Soil Quality, or Soil Health test packages. These packages test the biological activity in soils (active carbon, soil respiration, extractable protein), and physical characteristics (soil texture, aggregate stability, compaction, available water capacity), in addition to the traditional soil chemistry results (soil pH, organic matter, P, K, micronutrients). If using these tests, keep in mind that soils vary considerably from site to site. These results should be used as a baseline against themselves year over year, as opposed to comparing your results any listed “average”, or neighboring farms. These test results can be used as an indicator to evaluate the long-term effects of various soil health practices that you may be implementing. 

The appropriate soil test methods for a given region are selected based on soil characteristics and climate. Different analytical procedures can result in vastly different results. This is especially true of the different extraction solutions used to estimate a soil's nutrient supply. The two extraction solutions used in New England are the weak acid modified Morgan extract and the strong acid Mehlich 3 extract. These are both universal extraction procedures, meaning they are used to determine all major nutrients and many of the micronutrients simultaneously. Most New England Land Grant University labs (ME, VT, MA, and CT) use the weak acid modified Morgan extract. University of New Hampshire uses the strong acid Mehlich 3 extraction solution. A saturated media test using water as an extractant is used to measure nutrient availability in greenhouse potting media and in some cases, high tunnel soils. See Soil Testing Labs in New England (page 12) for contact information.

The quantity of extractable nutrients may be reported in different units. Some labs report the concentration of nutrients in ppm (parts per million) which is equivalent to mg/kg (weight basis) or mg/dm3 (volume basis). Other labs report nutrient values in lb/acre (weight per area basis). Nutrient concentration in ppm can be converted to lb/acre by multiplying by 2. This is based on the assumption that there are approximately 2,000,000 lb of soil in the surface 6 inches of one acre. Differences in reporting units are important to be aware of, but they are of little consequence to our interpretation of soil test results. Soil test results only provide an index of nutrient supply that must be interpreted based on correlation and calibration data developed by nutrient response research in local soils. It is important to understand what the nutrient interpretations mean.
 

Soil Test Interpretation

Soil test results are of little value without an appropriate interpretation. To be useful, extractable nutrient values must be shown to relate to: 1) the soil's ability to supply that nutrient to crops (correlation); and 2) crop response to application of that element (calibration). Figure 3 illustrates the conceptual relationship between soil test level and yield. This relationship is determined by conducting nutrient response research, under local conditions with representative soils ranging from deficient to adequate for each nutrient of concern. These data form the foundation of our interpretation of soil test results. The exact relationship between soil test level and crop response to different nutrients may vary considerably, but the general shape of the response curve is relatively consistent. At low soil test levels, yield is limited by a lack of the nutrient. As the soil test level increases, yield increases until a point where the nutrient is no longer limiting and the curve levels out; this point is known as the critical soil test level. The critical soil test level is defined as the extractable nutrient concentration in soil above which an economic yield (or quality) response to added nutrient is unlikely. Nutrient levels are considered sufficient when the concentration is just above the critical soil test level. This is known as the Optimum soil test range. Soil test values are interpreted based on how they compare to the critical soil test level and optimum range.  

SoilFig.1

Figure 3. Conceptual relationship between soil test level and crop yield or relative yield. The critical level is defined as the soil test level for a given nutrient above which there is a low probability to a response addition of that fertilizer.

Soil Sampling

A critical step in soil testing is sample collection. Be sure to read and follow sampling procedures from the specific lab you will be using. For all testing, it is important to obtain a representative sample; a poor sample may result in erroneous soil test results and poor recommendations. The first step is to determine the area that will be represented by the sample. Soil physical appearance, texture, color, slope, drainage, and past management should be similar throughout the area. It may be helpful to draw a map of the farm and identify areas where you will sample separately. Using a clean bucket and a spade, auger, or sampling tube collect at least 12-15 subsamples to a depth of 6-8 inches from random spots within the defined area and place them in the bucket. This may be accomplished by walking a zig-zag pattern across the sampling area and collecting a subsample periodically. Avoid sampling field edges, old fence rows, areas where manure or lime were stockpiled, and other non-representative areas. Next, break up any lumps or clods of soil, remove stones and plant debris, and thoroughly mix subsamples in the bucket. This step is very important, because only a few tablespoons of your sample will actually be used for testing. Once the sample is thoroughly mixed, scoop out approximately one pint of soil and, if specified by your lab, spread it on a clean piece of non-absorbent paper to air-dry (brown paper bags work great). Once the sample is dry, place it in a labeled container provided by the lab (or a zip lock bag), and complete a sample submission form. For each sample, indicate the crop to be grown, recent field history and any concerns.

Soil pH and extractable levels for certain nutrients (e.g., P and K) vary throughout the year. While the seasonal fluctuation is not typically large enough to significantly influence interpretation and recommendations, it can make it difficult to compare soil test values from the same field over time. For this reason, it is a good idea to be consistent about timing of sample collection from one year to the next. Although soil samples can be taken any time, many prefer to take samples in late summer or fall because this allows time to apply any needed lime, plan a fertility program and order materials well in advance of spring planting. Avoid sampling when the soil is very wet or within six to eight weeks after a lime or fertilizer application. Routine soil analysis should be conducted once every two to three years.

Soil Test Recommendations

Nutrient recommendations are determined by soil test results; however, even when two labs use the same methods and generate equivalent results, their nutrient recommendations may differ. These disparities arise due to differences in soil test interpretation and recommendation philosophies. Over the years, three basic philosophies have emerged. These include the sufficiency approach, the build and maintain approach, and the base cation saturation ratio (BCSR) theory. Both the sufficiency approach and the build and maintain approach follow the general concept that there are definable critical levels of nutrients in soil, and that below this level crops are likely to respond to additional nutrients applied. When nutrient concentrations are in the optimum range, just above the critical level, there is a low probability of crop response to the addition of that nutrient. With the build and maintain approach, fertilizer recommendations are made with the goal of building the soil's nutrient levels into the optimum range, then maintaining these levels by applying nutrients at rates that approximate crop removal. The sufficiency approach is a more conservative philosophy where nutrient recommendations are intended to meet crop needs, not build soil fertility. No nutrients are recommended above the critical soil test level. The sufficiency approach is designed to “feed the crop” while the build and maintain approach is designed more to “feed the soil.” In theory, the sufficiency approach is a more profitable system since fertilizer is only applied when there is likely to be an economic return. However, in practice the sufficiency approach is also more risky due to the inherent uncertainty associated with soil testing.

The third philosophy, the BCSR theory, promotes the idea that maximum yields can only be achieved by creating a balanced ratio of calcium (Ca), magnesium (Mg), and potassium (K) in the soil. At one time, many private labs and a few public labs used the BCSR concept to interpret soil test results and make nutrient recommendations. Over time, as the body of research evidence illustrating the flaws of the BCSR concept grew, leading most private labs and essentially all of the public labs to abandon the system. Most of the guidelines developed by Land Grant Universities and used by both public and private soil test labs follow a combination of the sufficiency and build and maintain approaches, the goal being to provide adequate, but not excessive, levels of essential nutrients to promote healthy plant growth. Nutrient recommendations provided in this Guide are a reflection of this compromise. The nutrient guidelines are intended to help growers optimize crop yield and quality, maximize return on fertilizer investment, and minimize nutrient losses to the environment.

The nutrient recommendation tables in this Guide are applicable to the New England soil test results given as very low, low, optimum (medium or high), and above optimum (very high or excessive). Table 5 provides a brief interpretation of each of these categories. Generally, nutrients should be in the optimum range for good yield and quality. When levels are below the optimum range (very low or low), the addition of more of the nutrient will usually improve production and provide a return on fertilizer investment. Nutrient recommendations are intended to meet crop needs and provide enough to slowly (several years) build soil test levels to the optimum range. When soil test levels are in the optimum range, crop response to application of that nutrient is unlikely, but some amount may be recommended to maintain soil tests levels by replacing a portion of crop removal. In the nutrient recommendation tables for each crop listed in the guide, these build and maintain application amounts are indicated by a range such as 0-50 lb per acre. Crops and even cultivars of the same species vary in their uptake and removal of nutrients and this is accounted for in the nutrient recommendations. If a nutrient is in the above optimum range, crop response is very unlikely and application of that nutrient is generally unjustified. It is important to keep in mind that factors other than nutrients may limit crop growth, and simply adding more nutrients will not improve yield. To optimize yield and maximize response to fertilizer nutrients, sound agronomic practices must be used (e.g., crop rotation, timely planting and harvest, pest control, soil health, and water management).  

Table 5: Interpretation of Soil Test Level Categories

Category

Interpretation

Very Low

Soil test level is well below optimum. Very high probability of crop response to additional nutrients.

Substantial amounts of additional nutrients required to achieve optimum yield.  Fertilizer rates based on crop response and are designed to gradually increase soil nutrient levels to the optimum range over a period of several years.

Low

Soil test level is below optimum. High probability of crop response to addition of nutrients. 

Moderate amounts of additional nutrients needed to achieve optimum yield. Recommendations based on crop response and are intended to gradually increase soil nutrient levels to the optimum range.

Optimum

Most desirable soil test range on economic and environmental basis. For most crops, low probability of crop response to addition of nutrients.

To maintain this range for successive years, the nutrients removed by crops must be replaced.

Above Optimum

The nutrient is considered more than adequate and will not limit crop yield. At the top end of this range, there is the possibility of a negative impact on the crop if nutrients are added.

Environmental Critical Level This soil test level is independent of crop response and, due to environmental concerns, is only defined for soil test P. This P concentration is associated with elevated risk of P loss in leachate and runoff at concentrations high enough to impair surface water quality. No P should be applied and steps should be taken to minimize losses from leaching and runoff.

 

 

 
 

Plant Tissue Testing

An additional tool that can be used for long season crops such as eggplant, pepper, potato, tomato, squashes, sweet corn, and pumpkin is plant tissue analysis.  While leaf tissue laboratory analysis can be used to verify symptomatic deficiencies in any nutrients, it can also be used to detect sufficiency levels of critical nutrients such as N, P, K, Ca and Mg.  If performed early enough in the season, corrections can be made by topdressing, side dressing, or fertigation.  Prior to making nutrient corrections, other potential issues should be addressed first, such as incorrect pH, inadequate soil moisture, root disease or insect infestation. Leaf tissue analysis requires collecting an adequately sized sample (from all over a planting) of whole leaves from designated locations in the plant canopy. These locations vary among crop species and specific sampling and handling instructions are available from university and private laboratories.  For the purpose of comparison, laboratory reports will also present results in tabular form alongside reference sufficiency ranges of nutrient concentrations for the crop tested. Nutrient status of some crops can also be determined using laboratory testing of whole leaf petioles, and for nitrate-N and K, it is possible to test petiole sap in-field using a portable meter.

Soil Testing Labs in New England

Connecticut:
Soil Nutrient Analysis Lab
6 Sherman Place, Unit 5102
Storrs, CT 06269-5102
Telephone: 860-486-4274
Website: http://www.soiltest.uconn.edu/
Email: soiltest@uconn.edu

Gregory Bugbee, State Laboratory
The Connecticut Agricultural Experiment Station
123 Huntington St., P.O. Box 1106
New Haven, CT 06504
Telephone 203-974-8521
Website: http://www.ct.gov/caes/cwp/view.asp?a=2836&q=378206
Email: Gregory.Bugbee@po.state.us

Maine:
The Analytical Laboratory and Maine Soil Testing Services
5722 Deering Hall, Room 407
Dept. Plant & Soil & Environmental Sciences
Orono, Maine 04469-5722
Telephone: 207-581-3591
Website: http://anlab.umesci.maine.edu/
Email: hoskins@maine.edu

Massachusetts:
UMass Soil & Plant Tissue Testing Laboratory
203 Paige Lab
161 Holdsworth Way
University of Massachusetts
Amherst, MA 01003
Telephone: 413-545-2311
Website: http://soiltest.umass.edu/
Email: soiltest@umass.edu
 
New Hampshire:
UNH Cooperative Extension Soil Testing Service
34 Sage Way
Durham, NH 03824
Telephone: 603-862-3200
Website: https://extension.unh.edu/programs/soil-testing-services
Email: soil.testing@unh.edu
 
Vermont:
UVM Agricultural & Environmental Testing Laboratory
262 Jeffords Hall, 63 Carrigan Drive, UVM
Burlington, VT 05405-1737
Telephone: 802-656-3030
Website: http://pss.uvm.edu/ag_testing
Email: AgTesting@uvm.edu
 
Private:
Woods End Research Lab, Inc.
290 Belgrade Road, P.O. Box 297
Mt. Vernon, ME 04352
Website: www.woodsend.org
Email: lab1@woodsend.org

Fertilizers and Soil Amendments

There are many ways to provide nutrients to meet crop needs and to build up a reservoir of nutrients in the soil. This section provides an overview of fertilizers and amendments commonly used in vegetable production systems.

Fertilizer recommendations for vegetable crops should be made in conjunction with a soil test report. Repeated use of the same amendments without regard to soil test level will likely lead to excess levels of certain elements, nutrient imbalances, poor return on fertilizer investment, and increased risk of nutrient losses to the environment. 

Fertilizers

Fertilizer grades refer to the guaranteed percentages of plant nutrients. The ratio refers to the proportion of nitrogen (N), phosphate (P2O5) and potash (K2O) in the fertilizer. For example, the grade is 5-10-5, and the ratio is 1-2-1. High analysis fertilizers are those with grades such as 20-20-20, 35-0-0 or 0-46-0, and are more economical to use on the basis of price per pound of nutrient.

Liquid starter fertilizers are materials that are completely water soluble and are high in phosphorus content such as 16-32-16, 10-52-17 or 9-45-15. These materials are used at the time of transplanting. Dry starter fertilizer can be banded at the time of seeding. The band is normally placed 2" below and 2" to the side of the seed. When using either dry or liquid starter fertilizer, follow label directions because an excess of starter could burn seeds and young seedlings. Starter fertilizer promotes early and rapid growth that leads to greater yields with certain crops such as tomato, pepper, and melon. See individual crops for rates.

Table 6, "Plant Nutrient Content of Various Fertilizer Sources" lists many fertilizers commonly used for vegetable cropping systems. Similar information for fertilizers and amendments commonly used in certified organic cropping systems are provided in the section entitled Guidelines for Organic Fertility Management (Table 10).


Table 6: Plant Nutrient Content of Various Fertilizer Sources (% by weight)

Fertilizer Source Material

Total Nitrogen
N%

Available Phosphoric Acid
P2O5 %

Water Soluble Potash K2O %

Combined Calcium Ca %

Combined Magnesium Mg %

Combined Sulfur S %

Ammonium sulfate

21

 0

0

0

0

23

Ammonium nitrate

34

 0

0

0

0

0

Anhydrous ammonia

82

0

0

0

0

0

Calcium nitrate

15

0

0

19

0

0

Calcium ammonium nitrate

27

0

0

0

0

0

Diammonium phosphate

18

46

0

0

0

0

Monoammonium phosphate

11

48

0

0

0

0

Epsom salts

0

0

0

0

10

13

Granulated Sulfur

0

0

0

0

0

90-92

Gypsum

0

0

0

19-23

0

15-18

Muriate of potash

0

0

60

0

0

0

Nitrate of potash

13

0

44

0

0

0

Nitrate of soda-potash

15

0

14

0

0

0

Nitrate of soda

16

0

0

0

0

0

Superphosphate

0

20

0

18-21

0

11

Sul-po-mag

0

0

22

0

11

23

Sulfate of potash

0

0

50

0

0

17

Triple superphosphate

0

44-46

0

13

0

0

Urea

45-46

0

0

0

0

0

 

 

Table 6a: Conversion Factors for Boron Nutrient Sources

Fertilizer Source Material

Boron content, %

Pounds of Material Required to Supply One Pound of Boron

Fertilizer Borate Granular1

14.30 (B)

7.0

Fertilizer Borate-48

14.91 (B)

6.7

Solubor

20.50 (B)

4.9

Fertilizer Borate-68

21.13 (B)

4.7

1 Best for fertilizer blends.

 

 

Manure

 

Animal manure is an excellent source of nutrients and organic matter. Many of the nutrients in fresh livestock manure, especially nitrogen, are readily available.  Nutrient content varies by animal species, their diets and the form of their manure. There are times when readily available nitrogen is needed, but many people prefer to compost manure before field application (see Compost section below). Manure application rates are now regulated in many New England States (see Nutrient Management Regulations).

Nitrogen in manures and other waste products: The N content of manures is highly variable. Differences are due to the species of animal, the animal's age and diet, the moisture content of the manure, handling and storage, and the amount of bedding in the manure. The N fertilizer equivalent of a manure varies not only with the total N content of the manure, but also with the timing and method of manure application. Manure samples can be analyzed by the Universities of Maine and Vermont Laboratories. The values in Table 7 are based on analyses of Vermont manures as well as published data from other states. If specific manure analysis data is not available, growers should estimate N credits using these or other book values. The time elapsed between spreading and incorporation of manure is also important. About half of the N in dairy manure and three quarters of the N in poultry manure is in the form of ammonium (NH4), which easily turns to ammonia gas (NH3) and is volatilized (lost to the air). The longer that manure is left on the soil surface, and not incorporated, the greater NH3 volatilization losses become (Table 7a). Broadcast application of slurry manure without incorporation should always be avoided because this method increases air contact and allows time for all ammonia to be lost. Research has shown that in reduced or no-till fields where manure must be surface applied without incorporation, ammonia can be best conserved if applied during cold temperatures, low wind speeds and especially to a growing cover. A growing cover also reduces manure run-off and leaching losses.  NOTE: Manure often contains human pathogens. Serious illness has occurred from eating produce where fresh manure was applied without an adequate waiting period (see Produce Safety).

Previous manure applications: Up to 50% of the total N in cow manure is available to crops in the year of application. Between 5% and 10% of the total N applied is released the year after the manure is added. Smaller amounts are furnished in subsequent years. The quantity of N released the year after a single application of 20 tons per acre of cow manure is small (about 15 lb N per acre). However, in cases where manure has been applied at high rates (30-40 tons per acre) for several years, the N furnished from previous manure increases substantially. The buildup of a soil's capacity to supply N resulting from previous applications of manure has important consequences for efficient N management, including: 1) The amount of fertilizer N needed for the crop decreases annually; and 2) If all the crop's N needs are being supplied by manure, the amount of manure needed decreases yearly.

With poultry manure (as compared with manure from cattle) a higher percentage of the total N in the manure is converted to plant-available forms in the year of application. Consequently, there is relatively less carry-over of N to crops in succeeding years. This does not mean, however, that there is never any carry-over of N from poultry manure applications. If excessive rates of poultry manure (or commercial N fertilizers) are used, high levels of residual inorganic N, including nitrate (NO3), may accumulate in soil. High levels of soil nitrate in the fall, winter and spring have the potential to pollute groundwater and coastal seawater.

Table 7: Nitrogen Credits from Manure Applied Before Planting

Type of manure Dry Matter Total N NH4-N Organic N P2O5 K2O
   

------------------------- lbs/1,000 gallons  -----------------

Dairy, liquid <5% 12-16 4.9 7.3 4.8 15.1
Dairy, slurry 5%-10% 22.3 7.6 14.7 8.9 22.0
    ---------------------------  lbs/ton  -----------------------
Dairy, semi-solid 10%-20% 8.5 1.8 6.7 4.1 6.1
Dairy, solid >20% 5-12 1.4 10.9 8.1 10.0
Beef (paved lot) 29% 14 5 9 9 13
Swine (hoop barn) 40% 26 6 20 15 18
Sheep 25% 23 n/a n/a 8 20
Poultry, layer 41% 16-37 18 19 55 32
Poultry, broiler 69% 75 15 60 27 33
Horse 20% 12 n/a n/a 5 9

Adapted from Nutrient Recommendations for Field Crops in Vermont (2018). Dairy manure values are from Vermont samples analyzed by University of Maine, 2012-2016, others are adapted from University of Nebraska-Lincoln NebGuide G 1335 and Penn State Agronomy Guide (2016). Values do not include bedded pack. Manures vary greatly, so obtaining a manure analysis is always best practice. n/a = data not available.

Table 7a: Availability of ammonium nitrogen from spring or summer applied manure (% fertilizer N equivalent)

 

Cattle1

Thin (<5% DM)

cattle

MEdium (5%-10% DM)

cattle

Semi-SOlid (>10% DM)

Cattle

Solid (>20% DM)

poultry

Solid (>20% DM)

Time to incorporation by tillage or rain -------------- % NH4 - N available to crop -----------
Immediate 95 95 90 95 95
< 8 hrs 80 70 60 80 90
1 day 70 55 40 60 85
2 days 65 50 30 45 80
3-4 days 65 45 23 35 70
5-7 days 60 40 25 25 60
>7 days, or not incorporated 60 40 20 10 50
1 Dairy cattle or other livestock.  Adapted from Nutrient Recommendations for Field Crops in Vermont (2018).

 

Compost

Composting livestock manure and other organic matter stabilizes the nutrients by partially decomposing the materials.  Nutrients are releaed more slowly from finished compost than from fresh livestock manure.  Compost is considered mature (i.e., finished) when most of the easily decomposed components of the material have been broken down and biological activity has slowed. At this time, the pile returns to ambient temperature, and it does not reheat when mixed or turned. The composting process results in a dark-brown material in which the initial constituents are no longer recognizable and further degradation is not noticeable. The length of time needed to achieve finished compost will vary with many factors and can range from a couple of weeks to over a year.

Application of unfinished compost could affect plant growth adversely because the compost-making microbes may compete with the crop for nitrogen. Applying compost at least one week before transplanting or seeding a crop will allow a margin of safety in case the compost is immature. Immature composts made from nitrogen-rich feedstock are also often high in ammonium, which can change to ammonia gas and be toxic to plant growth. High ammonium concentrations are not typically a problem if the compost is field applied, but if compost will be used in a greenhouse mix, it is important that it be low in ammonium. 

Vegetable growers can make compost on the farm although most don’t have enough raw materials to satisfy their needs. Some bring in additional materials such as manure or municipal yard wastes to compost on-site. Others purchase compost from commercial composters. 

Compost as a nutrient source. Finished compost is a dilute fertilizer, typically having an analysis of about (1-1-1 N-P2O5-K2O), but the analysis can vary greatly depending on the types of materials used to make the compost and how they were composted. Composts should be analyzed for their available N, total N, P2O5, and K2O content before application to agriculture fields.

Carbon to Nitrogen Ratio. The recommended C:N ratio for finished compost is 15-18:1. The C:N ratio plays a crucial role in the availability of nitrogen in any organic material added to the soil. If the C:N ratio is much above 30:1 microorganisms will immobilize (i.e., consume and make unavailable for plant uptake) soil nitrogen. This soil nitrogen will remain unavailable until the carbonaceous material is consumed by the bacteria.

Table 8: Typical Carbon-to-Nitrogen Ratios

Material

C:N RATIO
Legume hay 15-19:1
Non-legume hay 24-41:1
Corn stalks 42:1
Oat straw

70:1

Rye straw 82:1
Cow manure 18:1
Finished compost 17-20:1
Agricultural soils 8-14:1
Hardwood sawdust 500:1

 

Nitrogen. The majority (usually over 90%) of the nitrogen in finished compost has been incorporated into organic compounds that are resistant to decomposition. Rough estimates are that only 10%-30% of the nitrogen in these organic compounds will become available in the first season following application. Some of the remaining nitrogen will become available in subsequent years and at much slower rates than in the first year. Repeated annual applications of compost at high rates above 400 pounds of nitrogen per acre can result in excessive amounts of nitrate in the soil.

Phosphorus. There is not much research information published about the availability of phosphorus from compost. The few papers published show that composts made primarily from manures supply phosphorus over the growing season at 70%-100% of the availability of triple superphosphate fertilizer. The amount of organic amendments that can be added without building up excessive phosphorus depends primarily on: 1) the existing soil test P level of the field; and 2) the P2O5 content of the amendment. Table 9 shows the effect of both soil test P categories and the P2O5 concentration of an organic amendment on the suggested maximum amount of material to apply. If these rates of amendments are applied every year, analyze the soil for extractable P annually to ensure that soil test P has not risen to excessive levels. Additional compost applications to soil that tests optimum for P could increase P to above optimum levels. If a soil test shows an above optimum P level, avoid compost applications until P returns to the optimum range. 

Table 9. Maximum Compost or Organic Amendment Application and total P2O5 per Soil Test Category and P2O5 Concentration1

  Soil test phosphorus (P) Category
Compost/organic amendment P2O5 content Very Low/Low Optimum  Above optimum 
% P2O5 (dry wt.) P2O5 (lb/acre) Compost (tons/acre) P2O5 (lb/acre) Compost (tons/acre)  

Low (0.1%-0.5%)2

330 120 82 30 No application
Medium (0.5%-1.5%) 330 30 55 5 No application
High (1.5%-3.0%) 330 15 No application No application

1 Assumes moisture content of the compost or organic amendment of 45%.

2 Average rates used to calculate amounts of P2O5 applied for various rates of compost applications.

Potassium. Potassium in finished compost is much more available for plant uptake than nitrogen because potassium is not incorporated into organic matter. However, some of the potassium can be leached from the compost because it is water soluble. In one study, potassium levels were reduced by 25% when finished compost was left uncovered in the open over a winter.

Soluble Salts. In general, soluble salts are not a concern from additions of composts to field soil. However, soluble salts can be a serious problem when using compost in greenhouse mixes. Incorporation of 40 tons per acre of compost in the top 6 inches of field soil would be a ratio of 50 parts soil to one part of compost. Compost used in the preparation of greenhouse media will make up a much greater percentage of the whole mix and therefore will have a greater influence on all aspects of fertility, including soluble salts. It is important to have composts tested for salt levels. Electrical conductivity (EC) is a measure of salt level, and compost used in greenhouse mixes should have EC < 1 mmhos/cm.

Compost and pH. The pH of finished compost is usually slightly alkaline. In general, composts will not raise soil pH to undesirably alkaline levels because of the low total alkalinity of composts. However, caution should be taken if the compost has been “stabilized” with the addition of lime (thus increasing the total alkalinity) or with heavy applications to certain crops such as potatoes, for which the soil pH should be about 5.2. Heavy applications can cause increases in soil pH that might last for a growing season.

Heavy Metals and Trace Elements. The danger of heavy metals in some composts has received much attention. At one time, some heavy metals in some composts were high enough to be toxic to plants (copper, nickel, zinc) or of concern to human health (cadmium). There have been documented cases where elements such as boron have been raised to toxic levels with repeated applications of compost. These composts with high metals or boron were made from materials with high concentrations of these elements. Governmental regulations control the materials that may be used in composts for applications to farmland. None of these toxicity problems are likely to occur with compost that has been made from farm manures or crop residues or with the commercially available composts of today.

Herbicide Residues in Compost. There are broadleaf herbicides registered for use on turfgrass, pastures, and hay crops that retain activity in the manure of animals that have fed upon them, as well as through the composting process of crop residues from areas treated with these herbicides. There have been many cases where vegetable growers have unknowingly purchased organic amendments such as manure and composts that are contaminated with herbicides and have damaged vegetable crops. If you purchase organic amendments, you should be aware of this possibility and get assurance that herbicides are not present in the manures and composts that you purchase. 

Have Compost Analyzed. No compost should be applied to field soil or used in greenhouse mixes without testing for nutrient content. If the compost will be used in greenhouse mixes, it should also be tested for maturity. Some soil test labs will test compost. Check to be sure the lab analyzes compost before submitting samples, and make sure to have it tested as a compost sample, not as field soil.

Take Soil Test After Applying Compost. A good way to evaluate the effect of compost on the fertility of a soil is to obtain a soil test after applying compost. It is best to wait six to eight weeks after application before testing the soil to allow the compost and soil to equilibrate. 

Additional Nutrient Amendments

There are many different types of commercially available soil amendments and plant nutrient sources on the market today.   While some products contain detectable quantities of nutrients that become available to plants in the near term, other products may instead increase availability of existing plant nutrients in the soil. Many have not been well tested in controlled studies.  There are many  categories of such products available for purchase. Some, but not all, have been approved for organic production.

Organic Residuals

Organic by-products of industrial processes fall into this category. Note that the use of the word “organic” in this case refers to nature of the material itself, e.g. derived from biological sources. It does not necessarily indicate acceptability for certified organic production. Materials included in this category include processed slaughterhouse wastes, leather processing waste, biosolids, papermill sludge, and composts. In general, as these products decompose, plant nutrients are released. Many are sold with the nutrient analysis content listed, which is generally very low on a “percent-by-weight” basis. The greater benefits are usually for soil conditioning, and in some cases, liming activity. Not all of these products are acceptable for certified organic production, and acceptability for use in food production should be verified.

Foliar Amendments

Foliar feeding has become a more common practice among some vegetable farmers. Many products are now available on the market, for use in both conventional and certified organic production. Foliar feeding is not recommended as a major source of nutrients for a growing crop, but it can be used for supplemental feeding under certain circumstances. Such circumstances include: 1) when soils are cold and N and P mineralization rates are low; 2) at the onset of nutrient deficiency symptoms in rapidly growing plants (verified by properly conducted leaf tissue testing); and 3) during periods of high nutrient demand, especially fruiting. Even so, nutrient deficiencies often result from indirect causes, such as water issues, soil compaction, pH, root diseases or even macronutrient (N, P or K) deficiencies that can be limiting micronutrient uptake or availability. Addressing these issues is likely a more long-term, as well as time- and cost-effective way to ensure crop micronutrient needs are met.

New England soils are glacial in origin and are considered “young.” For this reason, our soils are not typically lacking in micronutrients. In soils with pH greater than 7, metal cations become less available to plant roots, and plants may show signs of deficiency. Most soils in New England are acidic, requiring periodic lime applications. Where soils are alkaline, the best way to correct deficiencies of Zn, Mn, Fe and Cu may be to apply foliar sprays of these nutrients in chelated form. Certified organic growers should ensure that they are using forms allowed under organic certification. In some cases, it may be necessary to lower soil pH using products such as elemental sulfur, aluminum sulfate or ammonium sulfate.

Plant Biostimulants, Biofertilizers, Microbial Biostimulants, Microbe-containing Bio-products

A biostimulant is a substance or microorganism (or mixture of one or more of these) applied with the intent of enhancing a crop’s nutrient efficiency, abiotic stress tolerance and/or quality traits, regardless of the material’s nutrient content. There are now hundreds of commercially available products that fall into these categories. This does not include products labeled for pest control purposes, however, which fall under strict EPA guidelines mandating EPA registration.

One category of these products is familiar to most: various strains of species of Rhizobium inoculants for legumes. Research has consistently shown the benefit of legume inoculation to realize full nitrogen fixation potential of legumes, provided that the plant and bacterial species are properly matched.

There has been a proliferation of mycorrhizal fungus inoculant products. These fungi are symbiotic with many crop plants (excluding brassicas and a few others) and extensive research has shown their beneficial effects on plant nutrition, growth, and stress reduction in field, nursery pot and greenhouse conditions. The fungi live inside plant roots, where they obtain a carbohydrate energy source from plants. In turn, the fungal mycelia transfer water and mineral nutrients to plants, which they can extract from the soil volume more efficiently. In this way, the fungi “extend” the rhizosphere that surrounds plant roots. Unfortunately, real-world test results of these products are not readily available. It is unknown at this time whether inoculation has short or long-term economic impact in annual vegetable production.

There are numerous other soil microbial inoculant mixtures available from commercial suppliers. Peer-reviewed research with many of these organisms has shown some positive potential. They are intended to influence crop plants’ rhizosphere, promoting potential availability of mineral nutrients already present in the soil, sometimes by stimulating plant responses to stresses or diseases. They do not, however, directly supply nutrient elements to plants. There may well be a promising future for microbial inoculants, particularly if it means reduced fertilizer input, but product effectiveness has not been well documented at this stage.

Compost Tea

The legal definition of compost tea from the National Organic Program is “A water extract of compost produced to transfer microbial biomass, fine particulate organic matter, and soluble chemical components into an aqueous phase, intending to maintain or increase the living, beneficial microorganisms extracted from the compost.” Microbial species content is highly variable, depending on the source of compost and the “brewing” conditions. Compost teas have a very low analysis of plant nutrients. Although they are widely produced and used on farms of various scales, research evidence of their efficacy is inconsistent at best. Benefits of using commercial microbial inoculants are variable, and using compost tea is even less dependable despite its widespread popularity. If you do plan to use compost tea, care must be taken to avoid cultivating bacteria harmful to human health (e.g., start with finished compost, use potable water, and avoid using additives like molasses).

Humates, Humic Acids, Humic Substances

These materials are made of very large and complex molecules. Most commercial products are extracted from peat or soft brown coal deposits of lignite. Extraction processes and treatments vary widely, so it is difficult to make comparisons between various products on the market. Humic materials contain only small amounts of plant nutrients, thus are not considered fertilizers. Their usage has been promoted by some to provide physical, chemical, and biological benefits to soils. These materials have been studied for over 50 years, mainly in controlled settings, with mixed results from laboratory and greenhouse studies; some resoundingly positive reports, many neutral, and a few detrimental. Under field conditions there are few documented positive effects from their usage. Naturally occurring compounds in soil organic matter effectively perform the same functions, such as chelation of micronutrient metals, and possibly producing plant hormonal effects. Nevertheless, there are many commercial products available, and little consistency among them.

Seaweed Extract Products

Seaweeds have been applied to agricultural land for at least a few thousand years and until recently, their primary benefit was considered to be similar to that of other organic amendments, releasing nutrients through decomposition. It was discovered over 50 years ago that seaweed nutrient content was too low to directly boost soil test nutrient levels and that other growth stimulating mechanisms must be involved. Seaweed has been proposed to have several different effects on the root zone environment and on plants themselves.

Though seaweed extracts are used in crop production in large quantities world-wide, there is surprisingly little published research on their use and effectiveness in field settings. One of the more common claims is alleviation of the effects of environmental stresses, such as temperature and moisture extremes. Subtle effects are difficult to measure in the field alongside many other possible factors. Therefore, when used during typical conditions, their effects are hard to detect.

Guidelines for Organic Fertility Management

A strong organic fertility program considers the interrelated factors of a given soil’s biological, physical and chemical characteristics to optimize and sustain crop production. Organic production emphasizes practices such as cover cropping, reduced tillage, and mulching to build soil fertility and to improve the physical and biological quality of soil. Bagged organic amendments also play an important role in organic production to supply essential plant nutrients to meet crop needs.

Organic matter management is the core of good soil fertility. Generous additions of organic materials, such as compost or green manures, are needed to feed soil microbes, which in turn leads to improved soil structure, aeration, and drainage. Improved water infiltration also indirectly supports healthy crops by promoting better root growth and helping plants access more nutrients and water. In addition, organic matter is the storehouse of nutrients in the soil. Many nutrients, especially N, P, S, Cu, and Zn, are mineralized and released when organic matter decomposes. 

Soil amendments used in organic cropping systems are typically complex, whole nutrient sources (e.g., compost, manure, seed meals and rock powders). Since many of these amendments provide multiple plant nutrients, it can become challenging to maintain nutrient balance over time. As a result, excessive levels of certain nutrients (especially phosphorus) may build up, especially when compost or manure based materials are repeatedly applied to meet crop nitrogen needs. Soil testing allows for monitoring these trends over time, enabling growers to adapt their nutrient management strategies to optimize yield, reduce costs of unnecessary nutrients, and minimize environmental impact. If a nutrient is rapidly accumulating, then adjustments should be made in the fertility program to provide only those nutrients needed. 

In general, the goal should be to maintain nutrient elements within the optimum range as reported on a soil test. When nutrient levels are within this range, the needs of most crops will be met. If levels are below optimum (very low or low), most crops will benefit by increasing levels to optimum. However, if levels are above optimum, there will be no additional benefit, and excess levels may reduce crop yield or quality, attract pests, and may cause environmental harm. This frequently occurs on organically managed fields where large amounts of manure or compost have been applied over the years. When a nutrient is above optimum it should not be included in any amendments applied until the excess is taken up by crops. See Soil Testing

Calculating nutrient contributions for organic materials can be difficult because nutrients are unevenly released during the growing season and may not match the timing of crop uptake needs. The rate of release is dependent on the type of organic material, and largely mediated by the C:N ratio of the material (lower C:N ratio = faster release rate). For example, compost, which primarily decomposes in the compost pile, is slower to release nutrients than manures (see Tables 10 and 10a below). The rate of release during the season is also dependent on soil moisture and temperature, both of which impact microbial activity. Cool, wet or dry soils typically slow decomposition and mineralization. In the late spring after the soil warms there is usually a flush of nutrients, and the rate of release commonly declines after that. When the release of nutrients is low, fertilizing with more available forms of nutrients may benefit crops. This is why crops may benefit if available forms of phosphorus and nitrogen are banded, or placed near the roots of crops early in the growing season. For example, use bone meal and a seed meal (like peanut or soybean) to provide some available P and N, respectively, or use a commercial organic fertilizer blend. See Tables 10 and 10a below for the nutrient content of several common amendments.

Nitrogen Anywhere from 10%-90% of the N contained in compost, manure, and plant and animal byproducts may become available to plants during the season following incorporation (Tables 7, 7a). OOn average, there is a release of about 10-20 lb N per acre for each 1% soil organic matter. These releases of N vary with drainage and other soil conditions, and may not be well timed to crop needs, especially for early, short season crops. Many annual crops need N most intensely about three to four weeks after transplanting, or just before the period of maximum growth. Therefore, sidedressing, or spreading a rapidly available source of N along the crop row so it will release nutrients at this time is most efficient. Examples of appropriate materials include feather meal, blood meal, seed meals, and dehydrated poultry litter. These materials are relatively expensive, so it is advisable to prioritize their use on high value crops. A PSNT collected at the right time can help estimate the most appropriate rate. See Nitrogen and Nitrogen Management under Plant Nutrients. 

Calcium is typically supplied in sufficient quantities by lime applied to manage soil acidity. When liming is not required and soil Ca tests below optimum, the best alternative source of Ca for organic producers is gypsum.

Magnesium is best applied as dolomitic lime, but when liming is not required, other Mg sources are Sul-Po-Mag or Epsom salts. Sul-Po-Mag is the better choice if potassium is also required. However, Epsom salts can be applied as a foliar spray to temporarily alleviate Mg deficiency. Dissolve 15 lb per 100 gal water and spray at weekly intervals.

Limestone is a widely used rock powder. It raises the soil pH and provides calcium (Ca) and varying amounts of magnesium (Mg). The appropriate rate of limestone should be determined by soil testing and adjusted based on the Calcium Carbonate Equivalence of the material. The selection of dolomitic or calcitic lime should be based on soil test levels of Ca and Mg. When Mg tests below optimum, dolomitic, or high-Mg limestone, should be used for liming. If Mg is optimum, a calcitic (low-Mg) lime may be used.

Phosphorus is low in many New England soils, and can limit crop growth, especially early in the season. Maintain a pH of 6-7 with limestone to maximize P2O5 availability. Compost and manures are an excellent source of readily available P2O5. Compost and manures tend to contain less P2O5 than N or K2O, but repeated applications of moderate rates will raise P levels substantially. Repeated use of these materials may result in excessive soil levels. Nutrient levels should be monitored with regular soil tests. If P levels are much above optimum, no amendments containing P should be applied (including compost), to reduce P levels over time.

Potassium is best applied at or near planting time because it is soluble and easily leached.  Sul-Po-Mag is the K fertilizer of choice when Mg is also needed. Potassium sulfate from natural sources is a better choice when K is needed but Mg is not.  Potassium is very slowly available over many years from granite dust and greensand, which may be applied at 3-5 tons to the acre to build up K reserves. Wood ashes contain soluble K, but must be used with caution because they can raise pH rapidly and can be caustic. The liming effect of ashes can be variable, though is often estimated as roughly half that of limestone. If large amounts are to be used, best practice is to have the material analyzed for both K content and Calcium Carbonate Equivalence (i.e., liming potential).

Micronutrients are generally sufficiently supplied to plants by regular additions of organic amendments. Wood ash is another excellent source of micronutrients. Some seaweed extracts may also supply micronutrients. In soils low in boron (B), especially sandy soils, remedial applications are widely recommended for crops that readily suffer from B deficiency, such as brassica crops. In this case, 1-2 lb per acre of B should be applied to the soil. It is difficult to apply such a small amount uniformly, but boron can be ordered either as part of a custom fertilizer blend. Alternatively, most boron products are soluble and, once dissolved, can be sprayed evenly over the soil. Several forms of B are OMRI listed, including Solubor, Fertibor and Biomin Boron. It is advisable to monitor B levels with soil tests and tissue tests (for perennial fruits). Excess levels of B are toxic to plants, and some crops, such as beans and peas, are quite sensitive to high boron levels (see Table 3).

Table 10: Typical Nutrient Values for Common Fertilizers Approved for Organic Production.

 

Total N (%)1

C/N ratio

Fraction of organic N made available first season2

P2O5 (%)

K2O (%)

Relative Availability3

Plant residues

 

 

 

 

 

 

Alfalfa meal

2-3

15-20

0.25-0.4

0.5

2.5

slow/med

Cottonseed meal

6

5

0.6-0.8

2

2

med/fast

Soybean meal

7

5

0.6-0.8

2

2

med/fast

Peanut meal

8

11

0.6-0.8

1

 

slow/med

Animal products

 

 

 

 

 

 

Dried blood

12

3

0.6-0.75

1

0.5

fast

Bone meal (steamed)

3

4

0.25-0.35

15

0

med

Bone char

0

-

-

15

0

med

Feather meal

13

4

0.6-0.8

0

0

med/fast

Fish emulsion

4

3

0.7- 0.9

2

0

fast

Fish meal

9-10

4

0.6-0.8

7

0

med/fast

Manure

 

 

       

Dairy, with bedding

1

18

0.3-0.5

0.5

1

med

Horse, with bedding

0.5

25

0.2-0.4

0.2

0.5

med

Broiler litter

3-4

15

0.4-0.6

3

3

med/fast

Layer manure

1-2

10

0.4-0.6

3

1.5

med/fast

Bat guano

6

2

0.6-0.8

9

2

fast

Compost (mature)

 

 

 

 

 

 

Manure

1.5-2

15-25

0.1-0.15

2

1

very slow

Yard waste

0.5-1

20-25

0.1-0.2

1

1

slow
             

Table 10a: Typical nutrient values for common mineral materials approved for organic production.

 

Total N (%)

P2O5 (%)

K2O (%)

Ca (%)

Mg (%)

Relative Availability3

Potassium sulfate (sulfate of potash)

0

0

50

0

0

fast

Sul-Po-Mag (sulfate of potash-magnesium)

0

0

21

0

11

fast

Epsom salts

0

0

0

0

10

fast

Wood ash

0

1

10

25

2

med/fast

Gypsum

0

0

0

19-23

0

med

Dolomitic lime

0

0

0

20-30

10-12

med

Calcitic lime

0

0

0

40

<5

med

Colloidal rock phosphate

0

254

0

20

0

slow

Rock phosphate

0

20-324

0

25

0

very slow

Granite dust

0

0

3-54

2

1

very slow

Greensand

0

14

4-94

0

0

very slow

1 Nutrient concentration of organic materials is inherently variable. Estimated values are provided for reference only. It is best to have materials tested in order to determine appropriate application rates. 

2 Compost, bat guano, poultry litter, and animal manures also contain varying quantities of NH4, which is immediately plant available; however, NH4 is subject to volatilization losses if material is not immediately incorporated.

3 Relative nutrient availability of lime and rock powders varies with origin of material, soil pH, and for rock powders, depends largely on fineness of grind.

   4 These values represent total K2O and P2O5. Available K2O and P2O5 from these materials will be much lower.

  

 

 

Reduced Tillage

The excessive tillage that occurs on most vegetable farms (plowing, harrowing, cultipacking, bed formation, cultivating) has many unintended consequences for soils and the environment. Some of the problems associated with excessive tillage include loss of organic matter and beneficial soil organisms; increased soil erosion and pesticide runoff; reduced soil fertility; loss of soil structure and porosity; compaction, surface crusting, formation of plow pans, reduced root growth, poor drainage, and reduced water-holding capacity. Results from a survey of 55 vegetable farms in Connecticut found that almost 90% of conventionally tilled vegetable farms had plow pans, compared with 33% for reduced-till operations, while the latter group had almost twice as much organic matter in their soils.

Tillage is also expensive and consumes a lot of energy. Reduced-tillage systems can often reduce fuel usage and reduce field preparation time by over 66% when compared with conventional tillage systems. These systems can provide equal or better yields than conventional tillage and may provide many other benefits as well.

Reducing the amount of tillage that takes place can help reverse the problems associated with excess tillage and begin to restore the health of a soil. A simple way to reduce tillage on your farm includes swapping from moldboard plows, disk-harrows and rototillers to using less impactful implements like chisel plows, subsoilers, s-tine cultivators and spaders. You may also work towards implementing minimum tillage systems such as strip-till, zone-till, ridge-till, no-till or permanent-bed systems. Most reduced-till systems are used in conjunction with cover crops or organic mulches to protect the soil surface at all times, help increase organic matter over time, or to help control weeds. Other examples of ways to reduce tillage include: 

  1. Using chisel plow shanks, subsoilers or zone-tillers to loosen soil before preparing raised-beds instead of a plow and harrow;
  2. Planting summer cover crops, such as buckwheat, after an early cash crop as a substitute for repeated harrowing to control weeds; 
  3. Mowing crop residues instead of disking; 
  4. Planting tillage radishes or other deep-rooted cover crops to help prevent plow pans from reforming; 
  5. Using a no-till drill to plant cover crops, instead of a harrow to assure good seed-to-soil contact for emergence.

Deep zone-tillage, also known as vertical-tillage, is one of the more promising and versatile methods of reduced tillage for vegetables in our climate and can help vegetable farmers reverse the ill effects of years of excessive tillage on their soils. Deep zone-tillage is similar to no-till in that it relies on the residue of a cover crop to protect the soil surface and help improve soil health over time. However, no-till relies on a heavy blanket of plant residue in the planting row to protect the soil, and inadvertently delays crop growth by keeping soils in the root zone cool in Northern climates. Deep zone-tillage addresses this issue by incorporating a 5-12"-wide tilled strip to simultaneously break up plow pans, prepare seedbeds and warm the soil. Planting and fertilizing can often be done in the same pass, further reducing fuel, machine hours, labor costs, fertilizer rates, and soil compaction. Soil drainage can be improved immediately and continues to improve each year.  The same herbicides, or some of the same cultural practices, are used to control annual weeds.

Implements used for deep zone-tillage usually consist of a lead coulter to cut through the killed-cover crop residue, followed by a deep shank or subsoiler to break up the plow-pan, and finally a pair of fluted coulters and a rolling basket to prepare a narrow seedbed and help break up soil clods. The deep shanks are mounted onto a hinged frame, which allows the shanks to rise out of the ground when they encounter large rocks or ledge, while spring resets push the shanks back down into position after passing over the obstacle. Crop roots grow deep through the slit made by the shank rather than just spreading out in the top few inches of soil above the plow pan. Additional coulters or (finger-like) residue managers are mounted on the planter in front of the planting shoes to remove excess cover crop residue and stones to provide finished seedbeds.

The soil surface between the crop rows retains the heavy surface residue from the dead cover crop. The 5-12"-wide tilled strip warms faster than residue-covered soils and, if installed across a slope, does not allow water to build up enough speed to erode a slope. Roots and surface residue from the cover crop in the untilled area between crop rows do not break down as fast as when the soil is tilled/aerated, so organic matter tends to increase over time. With the return of organic matter, comes the return of beneficial soil organisms, better soil structure, better water infiltration and holding capacity, and a healthier, more productive soil.

There are challenges to successful zone-tillage management. Killing cover crops and weed control can be problematic, especially with organic systems that do not allow herbicide use. Plant establishment can also be negatively affected by the presence of cover crop residues. Growers will need to be innovative to overcome these challenges.  Organic growers may try planting perennial rye or turf grass in the fall, and using a modified rototiller with the outside tines removed, to prepare narrow strips or seedbeds at the desired row spacing in the spring.  A subsoiler could be used to rip through the plow pan under the prepared strip to improve drainage. The living grass mulch between the crop rows can be controlled by mowing, while weeds within the row could be controlled by mulching, flaming or hoeing, or by planting competitive crops, such as summer squash.  At the end of the season, simply seed the strip back to turf.  The next season, move the strips mid-way between the previously prepared rows and switch crops to complete your crop rotation. 

There are other options to avoid using herbicides. Before early-planted spring crops, use fall-planted oats or a blend of cover crops that winter-kill, such as oats and tillage radish, before zone-tilling and planting. Cultivation can then be used for weed control over the relatively broken down cover crop residue. For summer vegetable plantings, use winter rye, but wait until it sheds pollen in June to crush it with a roller crimper, or cut and bail or windrow it to help suppress weeds between rows. Organic farmers who have worked most of the weed seed bank out of the top few inches of their soil through a combination of winter/summer cover crops, mulches, summer fallow periods and timely cultivations, may find it easier to adapt to zone-tillage than those fighting high levels of weed seeds in their soils. Note that specialized cultivation equipment will be needed to manage in-row weeds. The heavy residue or living mulch between rows will make mid-season cultivation of those areas difficult. Be sure to try this practice on small areas with low weed pressure. Small farms with equipment of insufficient size to pull a zone-tiller, might try lighter weight equipment to break through a plow pan and produce a seedbed, such as a Yeomans Plow, which can be pulled with 16-18 horsepower.

Strip-tillage, sometimes referred to as shallow zone-tillage, is similar to deep zone-tillage without the subsoiling shank to break up the plow pan. The implement has two or three closely spaced coulters and a rolling basket to prepare and smooth a narrow seedbed through the surface residue. Because the implement lacks a deep shank, this system does not have the ability to improve drainage immediately, and it may take several years for the soil health attributes and drainage to improve. However, on farms without a plow pan this system can provide most of the benefits of deep zone-tillage and uses less fuel.

Strips for cash crops can vary in width. To make wider strips in winter rye and vetch for late-planted vegetables, use a spader to prepare planting strips early in the spring when the rye just begins to grow, leaving equally wide strips of the cover crop to mature. A cultipacker or some other finish tool may be needed to smooth the seedbed for small seeded crops. Plant or transplant the cash crop in the prepared beds while the cover crop continues to grow between the beds.  To kill the cover crop, cut it when the rye is shedding pollen or when the vetch begins to flower, and spread the straw residue over the prepared bed as a mulch to help suppress weeds around the cash crop. It is best to cultivate the beds once before cutting and spreading the residue from the adjacent cover crops. Supplement the rye/vetch mulch with straw from a nearby field of rye.  

For early season vegetables, use a two-year system with spring-planted oats and field peas. During the first summer, after the cover crop forms seeds, mow it to get a thicker stand late in the season. After the cover crop winter-kills, use a spader to make planting beds for vegetables and use a straw mulch between beds or cultivate. A similar process can be done with medium red clover sown between or under a cash crop the first year.  When the cash crop is harvested and mowed off in late summer or fall, the clover will fill in to make a solid stand by spring.  A spader can then be used to make seedbeds for the new cash crop in the clover stand.  

No-Till planters have double-disk openers and closing wheels to create and close the seed furrow in unworked soil, through a thick cover crop residue. These planters rely on down-pressure springs and/or extra weight to assure that the seed furrow can be created, especially in a dry or compacted soil. If the accumulated crop residue is too thick or unevenly distributed the planters may also have residue managers to move some of the debris before planting. No-till planting can be used for late-planted vegetables in New England, after the soil has warmed under the cover crop residue. It works well for pumpkins and winter squash or summer plantings of sweet corn or other vegetables. When transitioning from conventional to no-till, yields have been known to decline slightly for a few years before recovering as the soil characteristics improve.

Ridge tillage is a reduced tillage system where the crop is grown on top of permanent ridges. This system works well for fields that are often too wet to work in the spring. To initially construct ridges, start in the fall with a tilled field, and broadcast a cover crop that will winter-kill, like field peas and oats. Immediately construct the ridges and roll them to flatten the tops. In the spring, use a flail mower to chop the dead cover crop residue followed by wavy coulters or a rotary hoe to loosen the top inch of soil. This scrapes away the old crop residue and flattens the top of the ridge in order to plant the new crop. The ridge is then restored to full height during the final cultivation. Usually two cultivations are required to help control weeds, loosen the soil and re-construct the ridges. Straw can also be used between ridges to suppress weeds. The ridges can be replanted for many seasons before they need to be reconstructed. As with many reduced-till systems, specialized equipment is required for planting, cultivating and possibly harvesting. Ridge tillage helps conserve moisture, lower inputs, and provide a warmer and drier soil environment for seeds.

Permanent bed systems help limit soil compaction and maintain soil structure. Equipment and foot traffic is limited to paths or tracks between the beds. Some permanent beds are raised structures while others are not. There are many different ways to construct permanent beds. One simple method is to use a spader to till the soil and provide a rotation between cover crops and cash crops to provide organic matter, nutrients, weed suppression and a great soil environment for healthy crops.  Mulch is often used with permanent raised beds to add organic matter and suppress weeds.

For example, you can use a perennial sod cover crop for wheel tracks to avoid compaction on the beds and to increase habitat for beneficial insects. Properly prepared weed-free compost can be used to fertilize and simultaneously mulch the beds for weeds. Organic growers have found that constructing raised-beds, and then using tarps or a thick layer of weed-free compost as a mulch, reduces weed seeds over time, and the same beds can be used for years, with straw mulch to control weeds between beds.      

Tarping or covering the field that has received some level of reduced tillage from no-till to shallow tillage has become a common practice for many mixed vegetable growers and is often used in combination with permanent beds.  Covering the field with tarps changes light, temperature, and moisture dynamics at the soil surface. Effects on these conditions, in turn, affect biological processes such as photosynthesis, weed germination, and insect and microbial activity, which regulate the availability of nutrients like nitrogen. The typical tarp size ranges between 16-50’ wide and 50-100’ long.  Weight and bulk is often the limiting factor to size selection. For example, a 50’ x 100’ 5 mil silage tarp weighs 150 lb when clean and dry. It is possible to purchase tarps less than 4 mil thick, but they often do not last longer than a single season. While 5-6 mil tarps contain more plastic, they typically last multiple seasons. 

Vegetable farmers in the Northeast increasingly use tarps to prepare beds with minimal or no tillage between crops. The keys to successfully using tarps in this capacity is that tarps must: 1) terminate any living plants (cash crop, cover crop, or emerged weeds), 2) help create a planting bed that is suitable for the following crop, and 3) provide adequate weed suppression in the early period of cash crop growth, if not longer. When applied in this way, tarps provide some or all of the bed preparation services typically provided by tillage. Tarps can help fill a niche for farmers using minimal tillage by creating weed-free planting conditions for the following crop.

Crop Rotation

Crop rotation is defined as a deliberate planting sequence over multiple growing seasons in which certain types of cash crops follow others. Such schemes are formulated for a variety of plant and soil health reasons.  However, on farms where soil health is a key focus of management, cover cropping and crop rotation schemes have overlapping functions and the two practices are intermingled. Here, the benefits and challenges of crop rotation are described.

A key principle of Integrated Pest Management (IPM) is the avoidance of pests and diseases using a variety of available means, giving preference to low impact prevention strategies over curative ones. One particularly effective and cost-free method involves moving crops of particular susceptibility from one location to another, season after season. This acts to break up the life cycles of some pests and diseases, as long as the next crop is an unsuitable host for them. Likewise for weeds, changing to a different crop may necessitate tillage at the time of a weed species’ greatest susceptibility.

A great number of crop pests specialize in feeding on plants of particular families or even genera. A well-known example is the Colorado potato beetle’s preference for members of the Solanum genus, especially potato and eggplant. For pests that are considered to be generalists, the strategy of crop rotation has minimal benefits. An example of this would be European corn borer, which can be a pest on corn as well as peppers, beans, potatoes, and many more crops, including ornamentals. Plant diseases also follow a similar pattern: Alternaria solani, known as early blight on tomatoes, potatoes and eggplant, is a specialist; Verticillium dahliae and Fusarium oxysporum have wide host ranges and so are difficult to control using a rotation strategy. Nevertheless, rotation is advisable whenever possible. If you have had trouble with an identified pest, check its host range and avoid planting a susceptible crop in the same plot the following season.

Growing the same crop season after season, necessitates the repeated use of similar cultural practices, including tillage, cultivation, fertilizer proportions, and timing within the season. Altering that sequence may explain the commonly reported 10%-15% corn yield increase when it is rotated with soybean, rather than continuous corn. In the case of vegetables, beans and peas, which are leguminous, can follow a crop with a heavy nitrogen demand, such as sweet corn, potatoes, and long-season brassicas. Rooting zone also determines where nutrient demand is greatest in the soil profile. Shallow-rooted crops such as salad crops, radishes and other short-season vegetables can be rotated with deeper-rooted parsnips, carrots, tomatoes and Brussels sprouts. Rooting depth also determines tillage depth, which is important to alter from season-to-season in order to avoid creation of a plow pan.

Various crops have different planting patterns in the field and impacts on the soil. Rotation between densely planted and widely-spaced crops changes water and wind movement patterns, helping to reduce erosion risk. The cultivation, hilling and harvesting of potatoes, as an example, all lead to the deterioration of soil health in those fields. A good crop rotation plan would follow potatoes by either a season of cover crop, or a cash crop such as a legume that has minimal impact on soil health. 

Developing a weekly crop plan for the current season is a great method to better planning cover crop systems and seed needs, communicating with your crew what needs to be done when, and for planning our rotations. Developing written multi-year rotation plans that include your full rotations plan (3, 4, or even 5 year rotations) help to visualize your full system including how fall crops or cover crops from one season will effect the spring planting of the following. There is an excellent workbook for this purpose from SARE (Crop Rotation on Organic Farms: A Planning Manual. Charles l. Mohler and Sue Ellen Johnson, editors.) Start by making maps and designating names to your fields. Use the USDA NRCS's Web Soil Survey, available at: https://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm.

Research has shown that cover crops can improve soil qualities in several respects and should also be incorporated into rotation schemes, including those that winter-kill, those that grow well into the spring, and those that fit into summer fallow periods. See the Cover Crops and Green Manures, below. The Northeast Cover Crop Council has developed the Cover Crop Species Selector Tool to help producers review traits of various cover crops, including optimal planting windows for fitting into crop rotations. 

Your rotation plan has to be tailored to fit your soils, climatic conditions, crop mix, equipment, and marketing plan. Finally, remember that no crop rotation will ever be perfect; there are always trade-offs. Some ideas for rotations that include cover crops and vegetables in New England are listed in Table 11. 
 

Table 11. Sample Rotations of Cover Crops and Vegetable Crops

 

Year 1 Year 2 Year 3 Year 4

Alternating Winter Crops/Vegetable Crops

Plow winter rye plus vetch

Late planted (warm season) vegetable crops

Oats in the fall

Disk Oats

Early planted (cool season) vegetables

Winter rye plus vetch in the fall

   
One Year in Cash Crops/
One year in Cover Crops

Plow winter rye/vetch

Transplanted vegetables

Winter rye in the fall

Plow winter rye in late spring

Sudangrass or two crops buckwheat

Oats plus hairy vetch in the fall

Mow vetch and plow residue

Direct seeded vegetables

Oats in the fall

Disk oat residue

Field peas plus triticale in spring

Sudangrass or two crops buckwheat

Winter rye/vetch

Two Years in Cash Crops/Two years in Cover Crops/Weed Pressure High

Plow rye or disk oats

Vegetables

Winter rye in the fall

Plow rye late spring

Early summer fallow then buckwheat

Oats plus field peas in the fall

Disk oats and field pea residue

Early summer fallow

Sudangrass or japanese millet

Disk sudangrass or japanese millet residue

Vegetables

Winter rye or oats in the fall

Two Years in Cash Crops/Two years in Cover Crops/Weed Pressure Low

Plow rye or disk oat residue

Vegetables

Oats in fall

Disk oat residue

Red clover and oats in spring

Mow oats once before oats form heads

Mow red clover 3 or 4 times

Plow red clover

Vegetables

Winter rye or oats in fall

 

Cover Crops and Green Manures

Cover crops are grown to protect and/or enrich the soil, rather than for short-term economic gain. When incorporated into the soil for fertility, a cover crop may be called a green manure. Cover cropping is an important component of vegetable crop rotations, as cover crops can maintain soil health and manage insect, weed, and disease pressure.

Cover crops can provide a range of benefits, depending on the species. Identifying goals and management priorities is key in selecting the best cover crop to use in a given field. Various cover crop types and species can protect the soil from intense erosion, alleviate compaction, suppress weeds, build SOM, add nitrogen, or scavenge excess soil nutrients until the following season. Fast-growing, thick cover crops are best for erosion control and weed suppression; high biomass cover crops add the most organic matter; legumes provide N; cold-hardy cover crops can take up nutrients that remain in the soil at the end of the growing season.

Cover crops can be added to a vegetable rotation at several points in the year.  They can be grown in the winter when sown in early fall, in the summer when sown in late May or June, as a spring cover sown as soon as the ground can be worked, as an intercrop between rows, beds, or blocks of vegetables, or as a long-term fallow in a field taken out of vegetable production for a season or more.

When growing cover crops from fall until spring, it is important to consider the cold hardiness and biomass production of potential species. Winter annual species, such as winter rye, dependably overwinter and provide large amounts of biomass by spring. Such species are suitable for subsequent warm-season cash crops, and work well for no-till and zone-till systems. On the other hand, high-residue winter-killed cover crops, like sudangrass, provide substantial ground cover over the winter (if seeded early in fall) while still allowing early spring planting.  Low-residue winter-killed cover crops like forage radish, oat, and field pea allow for planting of early season small seeded crops and are suitable for operations with limited tillage equipment.

Growing a robust cover crop stand requires good soil-to-seed contact, uniform seed distribution and seeding depth, and adequate soil moisture and fertility. A weak or spotty stand will not provide full benefits to soil health and can allow for high levels of weed growth within the cover. Recommended seeding rates for a cover crop vary depending on the equipment used and soil conditions. Drilling generally requires less seed than broadcasting, as it enhances soil-to-seed contact, and less seed is recommended for a well-prepared seedbed with optimal moisture and nutrient levels than for sub-optimal conditions. When broadcasting seed, germination rates can be improved through shallow incorporation, via tilling or disking, or rolling or culti-packing.

Having the appropriate termination equipment and labor is imperative to successful cover crop management. Letting cover crop biomass grow beyond what equipment can handle will make termination and incorporation efforts very difficult. It is also important not to let cover crops go to seed, which can happen when they are left to mature in the field. This can lead to long-term weed problems with some species.  Selecting appropriate, manageable species is key for avoiding these problems.

Fall-seeded cover crops. These include hardy small grains sown primarily for winter soil protection and nitrogen scavenging, and a few legume species. Small grain options include rye, barley, oats, wheat, spelt, and triticale. Rye is the most cold-tolerant and puts on growth even late into the fall when days are mild. It develops a root system that holds soil in place over the winter and in early spring. Oats and barley are not winter-hardy, and create a winterkilled ground cover that is easily incorporated before planting vegetables the following spring. Wheat, spelt and triticale grow more slowly than rye or barley and are easier to incorporate in the spring. Triticale can be sown earlier to produce more fall growth; spelt grows well on low N soils. Hairy vetch is the most winter-hardy annual legume cover crop. It may be planted alone or in combination with small grains, which will boost its biomass production and nitrogen delivery. Later plantings of these winter cover crops will result in smaller plants over the winter, so it is advisable to double or even triple the recommended seeding rate when sowing late in the fall. 

Spring-seeded cover crops. These are used to provide early-season soil cover, add organic matter, and provide some weed suppression after a winter-killed cover crop or on land left bare over winter. Legumes can be mixed with oats or barley, which serve as nurse crops to outcompete weeds as legumes get established. Yellow mustard can be used as a good source of organic matter, with potential for soil-borne disease suppression. It can also suppress weeds, as can annual ryegrass. These crops are sown as soon as the ground can be worked in early spring.

Early summer-seeded cover crops. These fast-growing crops are used primarily to suppress weeds and add organic matter. Common choices are sudangrass (or sorghum-sudangrass) and buckwheat. Both grow rapidly if there is sufficient warmth, moisture, and fertility. Sudangrass is preferable for adding to SOM, as it can produce tremendous amounts of biomass when grown for the entire summer. It also has a deep root system that reduces compaction, and it can reduce root-knot nematode pressure. If a cover crop is needed for less time, and/or if weed suppression is the main goal, then buckwheat is preferable as it covers the ground earlier than sudangrass, especially in early June, and needs only 35-40 days to produce most of its biomass whereas sudangrass needs 60-70 days.

Late summer-seeded cover crops. These are sown after an early-harvested vegetable crop, a month or two before frequent frosts (mid-August to mid-September, in most locations). Winter cover crops such as rye or oats are an option; when sown early, they will produce more fall growth. When sufficient growing time remains in the season, annual ryegrass, forage radish, hairy vetch, and various Brassica cover crops can be used.

Non-legume cover crops

Annual ryegrass, also called Italian ryegrass, is a turf grass with a dense, shallow root system. This root system tolerates compacted soil, making it effective at scavenging excess available soil N. It competes well with late summer annual weeds, as well as winter annuals that germinate in the fall, such as chickweed. This grass will tolerate a wide range of soils but performs best on moderately- to well-drained soils with high fertility. It is well-suited to undersowing after the last cultivation of a cash crop in order to establish a winter cover prior to harvest. Annual ryegrass is less expensive than perennial ryegrass, and is more likely to winter-kill; however, it may overwinter in milder areas. Sow from mid-summer to early fall at 10-20 lb/A if drilled, or 20-30 lb/A if broadcast.

Buckwheat is a very fast-growing summer annual used to protect the soil, add organic matter, and suppress weeds for a month or two between vegetable crops. It grows well on nutrient-poor soils, but requires good tilth and drainage. It decomposes rapidly, making it easy to incorporate. Timely termination is important (within 7-10 days of flowering), so it does not become a weed in subsequent crops. Sow from early to mid-summer at 50-60 lb/A if drilled, or 90 lb/A if broadcast.

Cereal rye, also known as winter rye, is commonly sown after cash crops are harvested in the fall. It is inexpensive, very hardy, an efficient N scavenger, and adapted to a wide range of conditions. The latest-sown cover crop, it produces ample biomass if allowed to grow into late spring. This adds organic matter to the soil, but can be difficult to incorporate prior to crop planting. Late spring growth must be carefully monitored to prevent full maturation and to allow time for the residue to break down. Otherwise, the carbon-rich biomass may tie up soil N, interfering with subsequent crop N requirements. Sow at 60-120 lb/A if drilled, or 90-160 lb/A if broadcast, from late summer to mid-October in most areas. Incorporate in spring before it gets too large for equipment to handle. Some growers leave narrow strips of rye untilled as windbreaks between blocks of crops in the spring.

Forage radish, oilseed radish, and tillage radish are late summer-seeded brassicas that are not winter-hardy. These crops form thick, white taproots that can grow 8-14 inches. Radishes are excellent at breaking up shallow layers of compacted soils; the end of the taproot can penetrate deeper layers of compaction. The roots die over the winter, leaving channels that allow soil to dry and warm up faster in the spring. Radishes also suppress fall weeds. However, some vegetable growers with several Brassica cash crops in their rotation avoid this cover crop, to minimize Brassica-specific pests and diseases. Plant into a smooth seedbed. Sow 4-10 weeks before fall frost at 5-10 lb/A if drilled in good soil conditions or 10-13 lb/A if broadcast or drilled into sub-optimal conditions. Sowing higher rates leads to overcrowding and weaker growth. Drilling produces a much better stand; broadcasting should be reserved for when the soil is too wet to drill. After seeding, roll the ground to improve seed-to-soil contact. Forage radish can be planted with 40 lb/A of wheat for spring cover and weed suppression. Higher seeding rates will increase leaf growth for weed suppression, while lower seeding rates will produce deeper tap roots for alleviating compaction.

Japanese millet is an annual grass that grows about 4' tall and can provide good weed suppression. It is about the stature of buckwheat but has a longer lifespan, providing ground coverage from early summer through fall without mowing if sown heavily. Sow at 20-25 lb/A if drilled, or 30-40 lb/A if broadcast. This species performs poorly on sandy soils without supplemental fertilization.

Mustard can be used as a fall-planted winterkilled cover crop. It adds organic matter, and suppresses weeds in the following crop. Soil-borne diseases are suppressed by glucosinolates in mustard and other Brassica family crops, but results may vary from year to year and across locations. Different species and varieties contain varying amounts of bioactive chemicals. To increase the benefits of biofumigation with mustards, the cover crop should be flail mowed at peak bloom and then incorporated immediately before a rain event. Plan to either roll the soil and/or cover the area with a tarp to trap in the gases from the glucosinolates. When planting, prepare a firm, weed-free seedbed with adequate levels of available N to ensure a good stand. Sow any time the soil temperature is above 40ºF and the field is available for 5-7 weeks at 5-12 lb/A if drilled or 10-15 lb/A if broadcast. Roll the ground to improve seed-to-soil contact, but do not break up soil aggregates. In the spring, yellow mustard can also be frost-seeded or sown as soon as the ground can be worked. Do not let mustards go to seed; they can easily become weed problems. Mustards attract flea beetles and diamond-back moths, and can host Brassica pathogens such as clubroot.

Oats are often used as a winter cover crop that protects soil without requiring intensive management in the spring, since they are frost-killed. Shallow incorporation of residues may still be necessary before crop planting. Enough growth is needed before first frost to provide adequate ground coverage, so plant from mid-August to mid-Sept in most areas. Sow 80-110 lb/A if drilled, or 110-140 lb/A if broadcast. Oat residues left on the soil surface can suppress weeds through allelopathy (chemical suppression), or via a physical barrier to emergence. Oats are a good cover crop species to plant any time during the spring or fall for quick coverage.

Sudangrass and Sorghum-Sudangrass (or sudex) are fast-growing, warm-season species that require good fertility and moisture to perform well. Under such conditions, their tall, prolific growth provides excellent weed suppression. The heavy growth can be difficult to cut and incorporate if left unmanaged. Sudangrass growth is easier to manage because the stems are narrower, and it can be sown a little earlier than sorghum-sudangrass. These crops provide abundant root biomass, which is useful for increasing SOM. Mowing when 2-3 ft. tall encourages root growth. Mowing several times during the season makes it easier to turn in residues later, and promotes tillering and root growth. These crops may suppress root knot nematodes. Sow once soil has warmed to 60ºF, in early summer at 35 lb/A if drilled, or 40-50 lb/A if broadcast. Provide adequate moisture and apply N fertilizer if grown on low-fertility soils.

Teff is a warm-season grass useful for suppressing weeds if sown at a high density. It has a fine plant structure that doesn't leave soil clumpy for the next crop. Although buckwheat and sudangrass are more common choices for early-summer cover crop species, teff tolerates dry conditions better. It also requires less maintenance compared to buckwheat, which must be controlled when it matures to prevent seed set, and sudangrass, which should be mowed several times. Teff needs minimal mowing and generally does not produce seed, so volunteers are not an issue. Sow in June-July into a very firm seedbed so that the tiny seeds stay near the surface. The crop needs 40-60 lb/A N. Sow 5-8 lb/A raw seed, or 8-10 lb/A coated seed or if soil moisture is uneven. Use a Brillion seeder or broadcast followed by roller or culti-packer to press seed into the soil. Needs frequent light rain or irrigation for rapid uniform emergence.

Legume cover crops

Legume cover crops are often used when "free" nitrogen is desired for a subsequent cash crop with high nitrogen demand. Legumes generally require good drainage and adequate phosphorus fertility (other than nitrogen). An abundance of available soil N will not inhibit growth, but reduce biological nitrogen fixation. Most legume species grow slowly at first, so they do not compete well with weeds until established. Drill seed for best stands. Treat legume seed with the appropriate inoculant to ensure optimum nitrogen fixation, unless the field has a known recent planting of the same species. Legume cover crops can be sown with a nurse crop such as winter rye oats to provide early ground cover and weed suppression during establishment. When legume cover crops with flower buds are mowed, tarnished plant bugs may be driven into adjacent vegetable crops.

Alfalfa requires deep, well-drained soil with a pH near neutral for good growth. It is a long-lived perennial that is probably not worth the expense of establishment in a short-term rotation; it makes more sense if also used for 2-3 years of forage production. Alfalfa fixes large amounts of nitrogen that can meet most or all of the needs of a subsequent vegetable crop if multiple cuts are made before it is turned in. Seed in early spring at 6-10 lb/A if combined with a grass nurse crop, or otherwise seed at 10-15 lb/A; drill if possible.

Hairy vetch is a winter-hardy annual legume that is an effective nitrogen fixer. It is useful in vegetable crop rotations as a tool for providing nitrogen without taking land out of cash crop production. Once established, it is good at weed suppression and soil conditioning. In most of New England, this cover crop is seeded in late summer, from mid-August to mid-September, and over-wintered. To gain the most nitrogen benefit, it should be allowed to grow until early flowering, about mid-May, before being incorporated. Sow vetch at 15-20 lb/A if drilled, or 25-40 lb/A broadcast. Use vetch/pea type inoculant (not crown vetch type). Since it is slow to establish, sow vetch with a nurse crop such as rye at 30-40 lb/A, or oats at 40-50 lb/A. The grass takes up unused soil N and ensures a good winter ground cover for erosion control, while also providing the vining vetch species a natural trellis to produce more biomass. Oats will not overwinter, leaving the vetch alone the following spring and making for easier management ahead of direct seeded crops. When planted with rye, more overall biomass is produced, which is more suitable for transplanting into rather than direct-seeding after termination. Hairy vetch can also be seeded in early spring or summer and allowed to grow until the following spring.

Red clover is a short-lived perennial that is somewhat tolerant of acidic and poorly drained soils. It is useful for adding nitrogen and organic matter to soils on land that is taken out of production for a season or two. Mammoth red clover produces more biomass than medium red clover, but does not regrow as well after mowing. Mammoth red clover will often establish better than medium red clover in dry or acid soils. Seed in early spring or late summer or undersow in early summer into corn, winter squash before it vines, and other crops if soil moisture is plentiful. Sow at 8-10 lb/A if drilled, or 10-12 lb/A if broadcast. It can be mixed with sudangrass, sown at half the recommended rate, seeded in early summer.

Sweet clover is a deep-rooted biennial (except for some annual types) that is adapted to a wide range of soils. It is a good soil-improving cover crop with a strong taproot that penetrates subsoils, reducing compaction. Yellow sweet clover is earlier maturing and somewhat less productive than white sweet clover. Sow in early spring or summer at 6-10 lb/A if drilled, or 10-20 lb/A if broadcast. Heavy growth is produced in the spring after overwintering. Incorporate in late spring or mid-summer at full flowering.

Soybean and Cowpea are warm-season legumes that have potential as cover crops sown in early summer to provide some weed suppression and add high amounts of nitrogen to the soil. They are sensitive to frost and drought. Though typically grown for their seeds, these crops will primarily produce foliage if long-season varieties are used in the Northeast. Forage cultivars may produce more biomass than horticultural varieties, which will optimize nitrogen delivery. Drill at 30-40 lb/A, or 60-100 lb/A if broadcasting; use high rates in sub-optimal conditions, or to improve weed suppression. Avoid damaging seed when handling. Plant into a firm seedbed and provide adequate moisture for good germination. Good soil-seed contact and well-drained soils are needed to establish strong stands. Use cowpea/peanut, or soybean type inoculant. These can be grown in mixture with Japanese millet or sudangrass; the latter is taller and may shade out legumes, so reducing seeding rates is recommended.

White clover is a low-growing perennial, tolerant of shade and slightly acid soil. Ladino types are taller than the Dutch or wild types. White clover is a poor competitor with weeds unless mowed. It is suited for use in walkways or alleys. Once established, it provides long-term cover, either alone or with a low-growing turfgrass. It can be used in high traffic areas to minimize soil compaction and improve soil health. White clover tolerates wet conditions. Sow in early spring, frost-seed in March, or seed in early fall, along with a turfgrass, at 3-9 lb/A if drilled, 5-14 lb/A if broadcast.

Cover crop mixtures are used to diversify benefits as well as provide resilience should one species or another fail. A grass will usually establish quickly, holding soil in place and ‘nurse' the legume along. By taking up available soil nitrogen, the grass promotes biological nitrogen fixation by the legume species. Fertilization with nitrogen, or the absence of mowing, favors growth of grass over legume. Planting multiple cover crop species can increase the number of benefits provided, but can also decrease the magnitude of each benefit. For example, several grasses and brassicas in a mix will result in less nitrogen fixed by legumes. Quick-growing, competitive grass and brassica species seeding rates should be reduced in mixes, while less competitive legumes should be kept close to monoculture seeding rates. 

Interseeding, or under-sowing a cover crop into a standing cash crop, is a way get a jump on the fall/winter cover crop season and can help protect soil between rows from erosion and compaction. When interseeding cover crops, sowing should be delayed enough to minimize competition with the vegetable crop, but early enough so the cover crop can establish well and then withstand the harvest traffic. Typically, a good time to sow is at last the cultivation, before the crop canopy closes. Less competitive crops such as carrots, onions, etc., are poorly suited to intercropping. Vigorous vegetables, like winter squash and sweet corn, can better tolerate early-summer interseeding with a cover crop such as ryegrass and/or red clover. Late summer is a better time for interseeding crops like peppers, staked tomatoes, fall crucifers, etc. Traditional winter cover crops like rye, oats, and/or hairy vetch can be used at that time. A good seedbed and timely rainfall or irrigation helps with establishment. Interseeding is not advisable when no irrigation is available, or if there are disease problems in the crop that necessitate post-harvest tillage. It should also be noted that interseeding cover crops can lead to increased rodent damage to crops like winter squash.

For more information:

Managing Cover Crops Profitably: www.sare.org/publications/covercrops/covercrops.pdf

Cover Crops for Vegetable Growers: www.hort.cornell.edu/bjorkman/lab/covercrops/

 

 

 

 

Irrigation

In most years there are at least some periods of inadequate rainfall. Even a short dry spell can adversely affect crop yield and quality. Irrigation requirements differ somewhat among the various kinds of vegetable crops, but they all benefit from supplemental irrigation when needed. It is critical to manage soil moisture to provide an ample and steady supply of water to crops without overwatering. Table 13 lists periods of critical water need by vegetable crops. Special crop requirements will also be discussed in each crop section of this Guide. General irrigation guidelines are presented here.

Contact your local Extension office to determine what information is available in your state. There are also several knowledgeable irrigation equipment suppliers who serve the New England area who can be very helpful. As you begin to plan your irrigation program, keep in mind that it is usually best to look first at the highest value crops you grow as well as the anticipated increases in yield and income with the use of irrigation. When buying equipment and developing water supplies, consider future needs.

General Irrigation Guidelines

Soil Moisture

A soil is saturated when all of its pore spaces are filled with water. This is likely to be the case after a heavy rain or irrigation. After one or two days, when excess water has drained due to gravitational pull, the soil is at field capacity. At this point, the remaining water is attracted strongly enough to soil particles to prevent further drainage, yet it is readily available for uptake by plant roots. Soil water is further depleted by evaporation from the soil surface and transpiration through the plant leaves. The combination of these processes is called evapotranspiration (ET). As soil water is depleted, what remains is held more tightly by soil particles. As this happens it is increasingly difficult for plant roots to extract moisture from the soil. Eventually a point is reached where the remaining water is so tightly held by soil particles that it is unavailable to plants. This is the permanent wilting point or wilting coefficient. Soil moisture in the range between field capacity and the wilting coefficient is usable by plants and is called available water, although moisture stress will occur as the lower end of this range is reached. It is advisable to begin irrigating vegetables before half the available water has been used. If soil moisture is depleted below this point, plants will be under increasing stress, even though they may not show visible wilt symptoms at first. Moisture stress can greatly reduce yield and cause numerous disorders such as tip burn of leafy crops and blossom-end-rot in tomatoes and other fruits. It may be advisable to begin irrigation when as little as 30% of the available moisture has been used.

To achieve the most benefit from an irrigation system, it is necessary to apply the correct amount of water at the right time. This means replacing the water lost through ET and doing so before plants are under stress. The rate of ET is affected by a number of environmental factors including solar radiation, temperature, wind speed and relative humidity. When it is hot, sunny and windy with low relative humidity, up to 1/3" of water per day can be lost through ET. That is about 2" per week. When it is cool, cloudy and damp with little wind, losses are quite low. As canopy area increases, evaporation from the soil decreases due to shading, but transpiration from the leaves increases and generally ET increases. If weeds are present, their leaf canopy increases ET losses to the detriment of the crop. Evaporation from the soil surface is reduced by the use of organic mulch and nearly eliminated under areas covered with plastic mulch.

Evaporation pans can be used to estimate ET loss. Pans should be filled with a measured amount of water, such as 1", and placed in or next to the field in a sunny spot. The loss of water from an evaporation pan will approximate the amount lost through ET. Although this is not exact, it provides a good indication of the rate of loss when sprinkler irrigation is used. When irrigation occurs, the evaporation pans should be filled with the same amount of water as was applied to the field.

It is important to know the amount of available water that a particular soil can hold. This varies considerably with soil type. For example, a slit or clay loam can hold several times as much available water as a sandy soil (Table 12). Soil organic matter can substantially increase a soil's ability to store available water. It has been estimated that for each percent of soil organic matter, water holding capacity is increased by about 1/2" per foot of soil depth. This depends on the state of decomposition, but it is clear that organic matter has a profound influence on moisture holding capacity. Crops growing on soils with a high available water holding capacity require as much water as those on a soil of low available water holding capacity, because ET is about the same on both types, but the required frequency of irrigation is different. Soils with a high available water holding capacity need less frequent irrigation than those with a low capacity. However, when irrigated less frequently, a greater amount of water should be applied per application. This results in less labor for moving and setting up pipes and sprinklers.

Table 12: Available Water Holding Capacity Based on Soil Texture

Soil Texture Available Water Holding Capacity
(inches of water/foot of soil)
Coarse sand 0.24-0.72
Fine sand 0.48-1.08
Loamy sand 0.72-l.44
Sandy loam 1.32-1.80
Fine sandy loam 1.68-2.16
Loam and silt loam 2.04-2.76
Clay loam and silty clay loam 1.68-2.52
Silty clay and clay 1.56-2.16

When to Apply Water

In general, if you wait for crop symptoms (wilting) to decide when to irrigate, the crop will already be damaged. While experienced growers learn their soils and how they interact with water over seasons of experience, utilizing a soil moisture measuring device or sensor of some sort enables a grower to attach a number to their observations and track trends over time. Readings provided by sensors can also be utilized to fine tune irrigation management strategies and better manage the growing environment for specific plants.  Proper installations of sensors is critical for accurate readings. Sensors can quickly and easily be moved from one location to another in order to better understand the dynamics of soil moisture in relation to soil types, irrigation cycles, topographical changes, etc., so long as the installation instructions are followed along with each move.

Soil tensiometers for measuring soil moisture are available at a cost of $75 to $100. They can be purchased through several field equipment suppliers. To use a tensiometer, place the porous tube of the tensiometer at the depth you desire moisture measurement. You can calibrate your tensiometer to a particular soil so irrigation is done when the tension on the gauge reads a certain value (a number specific to your soil and the crop you are growing). A maximum value (usually 30-35) would be used for a sandy loam soil and this value may vary with the particular tensiometer purchased. In utilizing tensiometers, be certain you are aware of soil variability within a given field. Three to four tensiometers per field may be needed to adequately account for this variability and, in addition, two depths (commonly 6" and 12") may be necessary to adequately reflect the most critically stressed areas. The 6" unit indicates when soil moisture near the surface is being depleted (begin irrigating) and the 12" one shows when the moisture has moved to the bottom of the root zone (stop irrigation). In a drip irrigation system, a rule of thumb is to place the tensiometer about 6" from the tape at a depth of one-third the entire root zone. During irrigation, the tensiometer indicates when field capacity has been attained at the depth of the porous tube.

Another type of soil moisture sensor gaining popularity in the northeast is the granular matrix sensor. This category of sensors provides a reading based on the electrical resistance between two electrodes embedded in the granular matrix within the sensor. The more soil moisture available in the soil, the lower the resistance and the number on the reader. This resistance reading is reported in kilopascals (kPa) or centibars. This measure of resistance can be used to better understand the force a plant root must overcome to extract water from a given soil. 

Established guidelines for maintaining soil moisture in specific crops and soil types are available. Using these recommendations, paired with visually observing the crop and soil, provides growers with additional information on which to base their irrigation decisions. In most soils, other than heavy clay, the decision to irrigate would generally happen in the range of 30 to 60 kPa. Differences in soil type should be considered when determining the appropriate range in which to irrigate. This is because different soil types have varying levels of plant available water at various soil moisture readings. To clarify, a soil moisture tension reading of 40 kPa in a sandy loam would mean that approximately 50 percent of the water in the soil is plant available. Comparatively, a loamy sand soil might have only 35 percent plant available water at the same 40 kPa reading. 

This reinforces the importance of knowing your soil type, along with monitoring soil moisture and visually observing crops and soil to make an informed irrigation decision. Additionally, the irrigation method makes a difference as to when a grower might decide to irrigate. For example, overhead irrigation is recommended to begin when the available soil moisture is no less than 50 percent, whereas drip irrigation, taking comparatively longer to distribute substantial volumes of water, should be started before the plant available water drops below 80 percent. 

When using drip irrigation on plastic-covered raised beds, during rain events where less than one inch of rainfall has fallen, run the drip irrigation system as normal.  When greater than one inch of rainfall has occurred, delay the application of water through the drip irrigation system.  

Critical Periods for Moisture Needs

Vegetable crops should not be under stress at any time. Each crop has its particular periods of critical moisture needs. In many crops (such as sweet corn, beans, and peas), the most critical period is during or just after flowering. These crops have flower development in a much more concentrated period of time. Other crops (tomato, peppers, eggplant, and potato) also have a critical moisture need during fruit or tuber development. Check individual crops for details (Table 13). Some crops, such as onions, potatoes, pumpkins and winter squash, benefit from dry conditions at the end of the growing season when the crop is curing.

Table 13: Critical Periods of Water Need of Vegetable Crops

Crop Critical Period
Asparagus Brush growth
Snap beans Pod enlargement
Broccoli, cabbage, cauliflower Head development
Carrots, radishes, turnip, rutabaga Root development
Corn Silking/tasseling and ear development
Cucumbers, squash, melons Flowering and fruit development
Eggplants, peppers Flowering and fruit development
Lettuce Head development
Onions Bulb development
Potatoes Tuber set and enlargement
Tomatoes Early flowering, fruit set and enlargement

Note: These are stages of critical water demand, but vegetable crops should not be subjected to stress at any time during growth

Water Application Rate

The application rate of irrigation should not exceed the infiltration and percolation rates of the soil. Infiltration is the entry of water through the soil surface and percolation is the downward movement of water through the soil. If the application rate exceeds either the infiltration or the percolation rate, water will accumulate on the surface and is subject to run-off and erosion. Soil compaction inhibits both infiltration and percolation and should be minimized. Soil crusting also interferes with infiltration. Soil organic matter reduces soil compaction and crusting. Compaction and crusting can also be minimized by using appropriate tillage practices and restricting traffic over the soil.

Sprinklers

Sprinkler size should be chosen based on the crop, distance between laterals, pumping pressure and volume, and the infiltration and percolation capacities of the soil. Sprinkler placement should be staggered with those on adjacent laterals. This provides a triangular pattern in the field. Sprinklers are designed to operate with patterns that overlap according to the manufacturer's specifications. A triangular arrangement with overlapping patterns provides the most uniform coverage.

Wet conditions are favorable to most diseases. Time the use of sprinklers so that foliage can dry rapidly when irrigation is complete. This is usually in the morning. Irrigating thoroughly to achieve field capacity to a depth of the majority of the root system, and never permitting plant stress, can reduce diseases. Irrigating more often than necessary may encourage disease development by maintaining wet foliage for long periods of time. This can also leach nutrients.

Frost Control

Early- or late-planted vegetables can be subjected to freezing temperatures in spring or fall. Using an overhead sprinkler system that applies about 1/10" of water per hour, during periods when the air temperatures in the crop canopy are below freezing, can reduce or prevent crop losses. Greater or lower applications may be necessary depending on minimum temperature, length of freeze period, and wind speed. Be certain to start irrigating before the temperature reaches freezing and continue irrigating until ice melts. The degree of protection depends on wind speed and other factors. However, protection below 20°F has not been attained.

Trickle or Drip Irrigation

A well designed trickle or drip irrigation system benefits the environment by conserving water and fertilizer and requires little labor to use once it is set up. Water is applied either on the surface, next to the plant, or subsurface, near the root zone. In dry years, fewer weed seeds germinate between rows because there is less water available beyond the plant root zone, although weed roots may grow toward the wet zone, especially when plastic mulch is used. With drip irrigation there is less evaporation than with sprinklers. Evaporation losses from the soil surface are further reduced when drip irrigation is placed under plastic mulch.

It requires some expertise to install and operate a trickle system. Consultation with a knowledgeable professional is wise. A poorly designed system can result in yield variability in the field due to areas of over- or under-watering and clogged lines. Trying to save money by cutting costs on initial equipment purchases will likely be more expensive in the long run. Any or all of these problems can completely offset the potential cost savings from using drip irrigation, but they can be avoided by using good equipment and proper design and installation.

Water source. Organic materials such as plant materials, algae, small living organisms, and inorganic sand, silt, and clay are likely to be found in surface water such as a pond or stream. Well water is likely to have some sand, silt or clay particles, although not as much as most surface supplies. These particles can clog the small diameter emitters in the tape. Filters are used to remove particulate matter as discussed later. Surface water might have contaminants from run-off, which can include pathogens such as Phytophthora.

Slope. A slope of 2% or less is the ideal for drip irrigation. Many fields in New England have slopes greater than 2%. A difference of 2.3' in elevation will change water pressure by 1 psi, decreasing as elevation increases and vice versa. The length of lateral lines, the pump size, and pressure regulators are chosen based on the slope. It is best to run the rows horizontally across a slope, but if rows must run up and down, it is best to have the water flow downward through the drip tape. Water should also flow downward in headers. This probably requires that water be pumped to the top of the field so it can flow downward from there. With slopes greater than 5%, pressure-compensating drip tape is needed.

Soil. The soil type determines the soil wetting patterns. Soil wetting patterns in turn influence the depth of the drip tape and the distance between emitters. The duration and frequency of irrigation are also determined by the soil type. Over-watering can move fertilizer away from the root zone. On sandy soils, water goes primarily downward rather than horizontally so emitters should be at relatively close spacing. Spacing between emitters can be greater in heavier soils where there is considerable movement laterally. In sandy soils, irrigate more frequently, but run the water for a lesser amount of time. In heavier soils, irrigate less often, but run the water for a longer duration. In both cases, this should lessen the chance of leaching fertilizers away from the root zone.

Drip tape should apply water uniformly throughout the crop root zone. The emitters should be close enough so that there is uniform wetting of the soil. As discussed above, the spacing of the emitters is affected by soil type. Drip tape should have a coefficient of manufacturing variation (CV) number that reveals how much variation in uniformity there is from one emitter to the next. A CV of 0.05 is considered excellent and a CV between 0.05 and 0.1 is acceptable. The rate of water delivery is a function of the size and spacing of the emitters and typically ranges from about 2.5-5.0 gallons per minute per 1,000' of tape (0.25-0.5 gpm per 100').

The length of the drip lines is another important consideration. The length is determined by the pump size, the field size(s), and the slope of the land. Any one of these factors will influence wetting uniformity because the emitters will discharge water at different rates if there are changes in pressure along the line. Because of variation in water pressure, tape is rarely laid out longer than a length of 400' on fairly level land and less on slopes. Tape should run across the slope, but if this is not practical, it should run downhill so the pressure loss due to friction is counteracted by the gain as the elevation decreases. If the tape runs up hill, there is a double loss due to friction and increasing elevation.

The choice of tape thickness, measured in mils, is based on how long you want the tape to last and the expected highest water pressure in the lines. The longer the tape is expected to be in the ground, or the higher the pressure in the lines, the thicker the tape should be. Tape thickness is usually between 4 and 10 mil, though thickness of up to 25 mil can be purchased. Tape can be reused for two to three years, but the labor costs of retrieving and cleaning the tape usually make this uneconomical for annual vegetable crops.

Placement of drip tape. The tape should be placed as close to the plant as is practical for the specific crop. This is critical on porous soils, but if necessary, tape can be placed between 6" and 12" from the plants on soils with good lateral water movement. Tape is often laid between double rows of crops such as peppers. The soil will be wetter on the side of the crop where the tape is and most of the roots will be concentrated there. The tape should be placed so that the emitters are pointed upward so that any particulate matter will settle away from the emitters after the water stops flowing.

Tape can be placed on top of the soil or a few inches below the surface. If tape is on the surface, it is easy to observe wetting patterns and to make repairs if needed. The disadvantages are that there is greater evaporation in the initial stages of the crop's growth and the tape is more likely to be damaged by production practices, wind, and animals. As tape is heated by the sun during the day, it expands and takes on a snake-like pattern in the row. This is particularly a problem with higher temperatures under plastic. This can be avoided by burying the tape.

Pumps. For a given area, trickle irrigation uses less water and at a slower rate than a sprinkler system. Therefore smaller pumps can usually be used. The required pump capacity is determined by the flow rate of the tape, total length of tape to be used at a given time and pressure loss due to friction and increases in elevation. Pump size should be determined when designing a system.

Filters. The choice of filter is based on the quality of the water passing through the system and drip application requirements.  Typical screen mesh size is 150 mesh (100 micron). The filter should be sized for the longest application flow rate needed.  Water particulates change through the growing season and filter flow rates are affected with dirtier water and more suspended particulates.  It is better to design a system larger than is required, compared to smaller.

Screen filter. Screen or mesh filters are inexpensive and easy to install. Mesh filters work well if there are moderate to low contaminants in the water, such as those coming from a well or public water supply. Screen filters have a limited ability to store contaminants. If the water comes from a river or pond, the screens will probably have to be flushed often. This could result in considerable down time and labor.

Mesh screen sizes are between 20 and 200 mesh. The larger the number, the smaller the particle the screen will filter out. The screens are made from stainless steel, nylon, or polyester. Follow the recommendation of the tape manufacturer as to mesh.

Disc filter. A disc filter consists of a series of discs that are stacked on top of each other. The discs have microscopic grooves that radiate out from the center and filter out particles. Equivalent mesh sizes are between 40 and 600 mesh. They require less water for cleaning than do sand filters.

Sand filter. Sand filters are preferred over screen filters if the contaminant load is moderate to heavy. A sand filter can run longer than a screen filter before it needs to be cleaned by back flushing. This results in less down time and labor. The filters can be set up in pairs so that clean water from one filter is used to back flush the other filter. A screen filter can also be used to provide clean water for back flushing a sand filter.

The correct filter size is important. Under-sizing will increase pressure loss and there is considerable down time for cleaning. It is better to be too big than too small. The sand used for trickle irrigation should be of the correct type, made up of crushed, sharp edged silica or granite. 

Pipe/Mainlines. Mainlines can be metal pipe, PVC pipe or lay-flat hose. They deliver water from the pump to the submains and laterals. Proper pipe diameter is a function of the pumping rate and distance the water must travel. Larger diameters can move greater volumes and have lower friction losses, but are more expensive than smaller pipes. The longer the pipe and the more elbows or junctions, the more pressure loss due to friction. A qualified designer can help determine the appropriate pipe size for the system.

Care should be taken when laying the pipe to prevent soil or debris from getting into the system and clogging the lines. The lines should be flushed before the tape is connected to remove any dirt that got into the lines during installation.

Back flow preventers or check valves allow water to flow in one direction only. They are used to prevent water from flowing backward into a water source after the system is shut off. This is especially important to prevent injected fertilizer or pesticides from contaminating water supplies. They are required by law for systems with injectors. In some areas they may be required even if no injector is used. Vacuum-relief valves are installed to prevent soil from being sucked into the emitters when a vacuum is created after the system is shut-off.

Pressure regulators maintain the desired pressure as the water flows through the system. They are required to supply the appropriate pressure to tape and may be needed to protect filters and other components. They should be sized according to the rate of water flow. Drip tape typically operates at 12 PSI. 

Running the System

 

Fertigation

Fertigation is the injection of soluble fertilizer into irrigation water. Nitrogen and potassium are available in liquid or soluble solid form and can be applied through a drip system. Phosphorus, if needed, is usually broadcast at the beginning of the season.

By using a fertilizer injector, trickle irrigation can be used effectively to apply N and sometimes K during the growing season. The need for supplemental N can be determined using the PSNT as it is with other application methods. Samples for the PSNT should be taken from under the plastic, if used. Use a soil sampler to punch a small hole in the plastic and remove a core of soil. Be sure to avoid cutting the irrigation tape when sampling under plastic.

With conventional topdressing or sidedressing, it is common to apply all the N in one or two applications. With trickle irrigation, it is convenient to apply small amounts of N weekly or even daily, which is desirable from a N management standpoint. For example, if you want to apply about 50 lb N per acre, you can inject a little over seven lb N per acre per week for seven weeks, or about one lb per day if you prefer. Small weekly applications provide for more efficient crop use of N than one or two larger applications. Daily application offers little advantage over weekly application, but may be necessary if the injector cannot inject a week's worth of N during the appropriate irrigation run time. To prevent leaching, the irrigation system should not run longer than necessary to effectively wet the root zone of the crop. If there is not enough time to inject all the fertilizer needed for the week in one injection, then smaller, daily injections are preferable. Before injecting fertilizer, the entire system should be filled with water at full operating pressure. When all the fertilizer has been injected, the system should run long enough to flush all fertilizer from the lines. If fertilizer is left in the lines, clogging may occur due to chemical precipitates or growth of bacterial slimes.

Water Problems

Certain fertilizer materials may react with chemicals in irrigation water. If the water pH is below 7.0, there is little potential for problems, but at pH 8.0 and above, the risk is high. At levels above 40-50 ppm, calcium and magnesium are likely to react with phosphorus, if present in the fertilizer, causing precipitation of phosphates. If fertilizer containing calcium is added to water with concentrations of bicarbonates above 2 meq/liter, calcium carbonate may precipitate. Sulfates in fertilizers can react with calcium in the water resulting in the precipitation of gypsum. These precipitates can clog emitters.

Phosphorus- and sulfate-containing fertilizers, if needed, should be applied before planting because we are not concerned about these leaching. Nitrogen is the element that is most appropriate for injection into trickle irrigation water. Calcium nitrate has the potential to cause clogging if the water pH and bicarbonate levels are high, as noted above. If calcium nitrate causes clogging, potassium nitrate or urea can be used as an alternative N source.

Water testing labs can analyze water for pH, calcium, magnesium and bicarbonates. You can also perform a simple test: Mix fertilizer into a container of irrigation water at the same concentration it will be after injection into the trickle system. Cover the mixture to exclude dust and let it sit for at least the length of time it will be in the system before it reaches the soil. If the water becomes cloudy or a precipitate collects on the bottom of the container, you can expect this to happen in the irrigation system with the likelihood of clogging. If it is necessary to lower the water pH, acid can be injected into the irrigation water. This requires special handling precautions and special injection equipment. Be sure to carefully follow directions to avoid personal injury or damage to crops or equipment.

Raised Beds

Raised beds provide an optimum environment for germination and growth, especially when used with the stale seedbed technique. Raised beds are formed with special bed shapers. Raised beds improve drainage and hasten the drying of soil. Without irrigation, bed height should be restricted to 4". When irrigation is available, bed height can be raised to increase air flow and benefit crops such as lettuce. In areas of heavy rainfall, crops are seeded on beds so that excess water drains off. Yields of vegetables such as carrots and parsnips, where root length is important, are often increased because the depth of friable soil is greater. Pre-formed raised beds warm up faster and allow for early seeding. Raised beds can also reduce the incidence of Phytophthora root rot, damping off, and feeding by slugs because raised beds can drow out more quickly than flat beds. Herbicides are often incorporated into the soil at the same time or just after the beds are made. Be certain that the herbicide is incorporated to the proper depth. For best results, do not incorporate the herbicide before the beds are made; the herbicide will likely end up too deep and cause crop injury; or concentration can be increased when soil is piled up while forming the beds.

Wind damage is reduced with raised beds. Level soil has a more pronounced airfoil effect, and with the wind passing over them, this allows for a partial vacuum effect. Soil particles are more easily lifted and seedlings more often twisted. The resulting abrasions on the plant surfaces allow for easier disease introduction if conditions are favorable to the pathogens. Raised beds break up the airfoil effect, reduce the twisting of seedlings and the number of airborne soil particles. Wheel traffic is also restricted to a narrow zone between the beds.

Growers should consider bed direction and the slope of the bed. During cool, spring days, maximum warming of the bed is needed to provide suitable conditions for plant growth. When the days are short and temperatures are low, orient the beds north and south if two rows per bed are used (if soil erosion is not a consideration). If beds are set in an east-west orientation, the rows planted on the south side of the bed get more heat and grow faster than rows planted on the north side of the bed. This can lead to a lack of uniformity at harvest time. However, beds that are oriented across the slope following the contour of the land minimize soil erosion. For instance, on south-facing slopes, beds of spring crops should be oriented east-west.

Plastic Mulch and Row Covers

Plastic mulch and row covers are cultural tools that can improve earliness and yields of many vegetable crops. The primary function of these materials is environment modification, and their effectiveness is strongly influenced by the weather during a particular growing season. Row covers can also have pest management benefits. They can be used as a part of an overall production management program.

Plastic Mulch Films

Plastic mulch is generally 0.75-1.25 mils thick, 4-6 feet wide, in rolls 1,000-4,000 feet long. It is available in a multitude of colors ranging from clear (transparent) to opaque (black or brown). Recently, colored mulches have been investigated for their influences on insect control and plant yields. For example, reflective or silver mulches have been shown to reduce the incidence of onion thrips and aphids. Check with your local extension office for the most recent research findings proven to work in your area.

Plastic mulch functions to warm the soil, conserve moisture, and prevent nutrient leaching. It also protects ground-level fruit from soil pathogens. However, plastic mulch restricts rainwater from reaching to the roots. Therefore, drip irrigation should generally be used with plastic mulch. Clear plastic has the highest soil warming capability (8º-14º F over bare soil), but weed growth underneath can be extreme. An herbicide is necessary to keep weeds under control with clear mulch. Black mulch will prevent weed growth by prohibiting light transmittance to the soil and will warm the soil 3º-5º F over bare ground. On the other hand, white-on-black (white on the top) mulch is used to cool the soil.

Wavelength selective or near-infrared transmitting mulch (formerly referred to as IRT mulch, but now "IRT" is part of a trade name) is a "hybrid" of black and clear mulch characteristics. They are more expensive than conventional plastics. Specific pigments incorporated into the film during manufacture selectively block out blue and red wavelengths of light (which cause weeds to grow). This inhibits weed growth similar to black mulch. At the same time, infrared light is transmitted through the mulch warming the soil (similar to clear mulch). The wavelength selective mulches are generally brown or green in color. However, don't purchase them on color alone. The pigments embedded in the plastic impart these specific properties. Commercial recommendations are to lay wavelength selective mulches 7 days prior to transplanting. Within reason, the additional cost for this mulch film is compensated for by increased yields due to early soil warming. On small farms or in small fields, black, brown, or wavelength selective mulches are often the preferred way to eliminate the use of herbicides. This is a viable option for weed control on many organic farms. Crops that respond best to mulching are those that require higher soil temperatures (e.g. muskmelon, watermelon, cucumber, squash, tomato, pepper, okra, and sweet corn).

Apply plastic mulch after fields have been leveled and smoothed and fertilizer has been applied, and when there is good soil moisture (at or near field capacity, which is the amount of moisture left after a rain or irrigation event after surplus water has moved out of the root zone by gravity). In the case of black mulch, good uniform soil contact is essential as the soil is warmed by heat conduction. Commercially, the simplest way to apply mulch film is with a mechanical mulch layer. Plastic mulch can be laid flat against the ground or on raised beds. Raised beds offer additional soil drainage and early warming. Hand application is an option, but applying more than a half-acre can be difficult and time consuming.

Generally, plastic mulch is laid in the spring as soon as the land can be prepared. However, some spring seasons are wet and can delay normal land preparation and planting activities. An alternative is to lay plastic in the fall. Fall mulch application will require similar land preparation as in the spring, but use of a cover crop between the rows is recommended to prevent soil erosion. Oats will winter kill, but winter rye will need to be terminated by using an herbicide (such as Roundup or Gramoxone), or by mowing and cultivation.

After harvest, plastic mulches should be removed from the field and disposed of properly according to local ordinances on incineration and landfills. Alternatives to minimize disposal challenges of used PE are biodegradable mulch films and recycling programs to alleviate landfill accumulations. Recycling is very difficult to implement because mulches are dirty after field use, recycling facilities are limited, and it can be challenging to transport used plastic to recycling facilities. Soil and plant debris adhere to the mulch, adding up to 70% by weight and the presence of soil can abrade the recycling equipment. Research is ongoing to assess the potential for recycling the plastic into higher value products through pyrolysis and other chemical recycling methods that can accept some level of soil and debris in the used plastics.

Biodegradable Plastic Mulch

Degradable plastic mulch has been in development for decades. Some of the first commercialized products were photodegradable, and would break down when exposed to light. Many growers who used these products reported uneven and incomplete breakdown, particularly after tillage buried the plastic fragments at the end of the season. However, degradable mulches prepared from biodegradable polymers now exist. They are designed to be tilled into the soil after their service life, after which they will undergo aerobic biodegradation by soil microorganisms, producing CO2, water, and microbial biomass.

The most widely available and studied biodegradable polymer is Mater-Bi, made in Italy by Novamont. Some mulches that use this polymer are Bio360 and BioTelo (Dubois Agrinovations) and BioAgri (BioBag Americas). Mater-Bi is made primarily from starches, cellulose, vegetable oils plus proprietary biodegradable complexing agents derived from renewable, synthetic, or mixed sources. While Bio360 mulch is approved for use on European organic farms, at this time no biodegradable plastic mulch is approved for use on USDA-certified organic farms. This is because currently available biodegradable plastic mulches have a maximum 25% biobased content while one of the requirements of National Organic Program is that the mulch must be completely biobased. Further, most commercially available biodegradable plastic mulches are produced through fermentation using genetically modified yeast and bacteria for increased productivity, and that is not allowed in US organic agriculture. US organic regulations do allow the use of synthetic (polyethene) mulches, but they must be removed from the soil at the end of the growing season.

Research has shown that the biodegradable plastic mulches performed comparably to polyethylene mulch in controlling weeds, raising soil temperatures and increasing crop yields despite some breakdown of biodegradable mulch during the growing season. Biodegradable mulch does not have a significant impact on soil quality. Research at Washington State University modeled five years of mulch degradation data from a field study and predicted the timeframe of 21 to 58 months for 90% degradation of biodegradable plastic mulch after tillage. As biodegradable mulch starts to degrade during the growing season, mulch adhesion to fruit surface can be an issue for heavy-fruited crops like pumpkin and watermelon, where fruits rest on the mulch for extended period. Up-to-date information can be accessed at https://smallfruits.wsu.edu/plastic-mulches/.

Biodegradable mulches can range from 2-3 times the cost of standard black plastic, but end-of-season labor and disposal costs are avoided. The mulch is thinner (it comes in 0.5-0.8 mil thicknesses) than typical black polyethylene (1.25 mil), and when starting to lay the plastic, extra care is required to prevent tears. When laying mulch, do not stretch as tightly as you normally would with black plastic. Applying in early morning when temperatures are cooler can help. The mulch starts to break down more quickly when stretched. Apply right before planting because the mulch will start to break down as soon as it makes soil contact. Buy what you need each year – do not try to store biodegradable mulch. The mulch can start to break down in storage, particularly if storage conditions are moist and/or warm. Store the mulch upright, on ends of rolls. The mulch can start to degrade or stick together under pressure of its own weight. Biodegradable plastic mulches undergo degradation even under ideal storage conditions and may perform best if deployed within 2 years of their receipt date.

WeedGuardPlus (Sunshine Paper Co.) is a brown paper mulch with soil-cooling properties. It is OMRI listed and is effective under low rainfall and low wind conditions. WeedGuardPlus is also effective in controlling nutsedge unlike polyethylene and biodegradable plastic mulches. However, it is more expensive than biodegradable plastic mulch. 

Slitted and Floating Row Covers

Row covers function to enhance growth and yield by modifying the temperatures around plants in the spring and fall, or in combination with low tunnels, during the winter. They are also used for frost, hail, and wind protection, and to exclude certain pests. There are two general types: slitted or perforated plastic, and spun-bonded fabric. Heavier weight row covers can provide several degrees of frost protection, while lightweight "non-heating" or summer weight covers offer less heat enhancement and can be used in summer for insect protection. These materials can be used with or without hoops ("floating row cover") depending on its weight and the fragility of the crop underneath. Newer types of knitted or woven lightweight row cover (for example, 'ProtekNet' by Agrinovations) are available; they can be used with or without hoops, are quite durable, and will exclude insects. 

Row covers are installed right after planting and are left covering the crop for several weeks, depending on crop type and season. For fruiting crops and cucurbits, covers can be left in place for approximately 3-5 weeks until pollination is needed or the crop outgrows the space under the cover. Other crops that are low-growing and do not require pollination can remain under cover as long as the temperature benefit is useful. Sweet corn may be left covered with spun-bonded row cover until pretassel stage. If the crop is pressing against the cover, either loosen or remove it. Row cover removal timing is more critical in some crops, such as tomato and pepper, as they cannot tolerate extremely high temperatures that might develop under the covers (especially polyethylene). Covers must be removed for crops requiring insect or wind pollination.

Slitted or perforated row covers are clear polyethylene films with slits cut or holes drilled to provide ventilation when the plastic loosens under hot conditions. Under cool conditions, the plastic is taut and the slits remain closed. Very little water condensation occurs under perforated plastic covers. There is generally less frost protection under slitted or perforated row covers than under a solid cover. 

Plastic row covers will require support with wire hoops. A piece of No. 9 wire cut about 65" long makes a hoop that is about 3' wide at the base and 14" tall in the center of the row after inserting each leg of the hoop in the soil. Secure the edges of the cover with soil.

If you have a diversified vegetable and/or berry operation, row covers can be a cost effective and convenient tool for producing early, high quality crops. Edges are usually held down with soil, soil-filled bags, boards, smooth saplings or tree limbs or rocks. Row covers provide sufficient growth enhancement by raising air temperatures during the day and moderating cold temperatures at night. They also allow light and water to penetrate to the crop. The result is earlier harvests, and in some cases, higher total yields. While lightweight row covers do not provide reliable frost protection, they may be helpful when temperatures drop 2º-3ºF below freezing. Heavyweight covers can provide more frost protection, but they block much of the sunlight, resulting in slower growth. A key benefit of row covers is that, if they are sealed along the edges, they exclude a wide range of insect pests that can damage crops.

Which types to use? There are several different weights, measured in ounces per square yard, ounces per square feet, or grams per square meter. Materials that are 0.5-0.6 oz/yd2 provide growth enhancement and insect control, have high light transmission (85-90%), and are less expensive than heavier materials, but are more likely to rip from wind and sharp objects (fingernails, boots, deer hooves, stakes, etc.). One can expect 2 seasons with careful handling. A row cover that is 0.9-1.25 oz/yd2 is heavy enough to be more tear resistant and last several seasons, has somewhat lower light transmission (70%), and provides growth enhancement and some frost protection in spring and fall. The heaviest covers are 1.25-2 oz/yd2, have lower light transmission (30-40%), are used mainly for frost protection or for overwintering, and are durable enough to last for several seasons when handled with care. Non-heating row covers are useful when an insect barrier is needed during the hot part of the season.

Support and fastening. Many crops can handle floating covers without any support, including lettuce, greens, crucifers, onions, potatoes, strawberries, sweet corn. Those with tender, exposed growing points (tomatoes, peppers, and vine crops) should have some support to prevent damage from wind abrasion. Wire hoops or short stakes with a smooth top to prevent tearing placed at 3- to 6-foot intervals provide good support. Secure the edges of the cover with soil, with soil-filled plastic bags, or with metal or plastic pins or staples. For holding the cover in place, soil is the most secure in high winds, but the edges are difficult to unearth after repeated wetting and drying, while soil bags make it easier to lift or move covers and prolong the life of the material.

Widths. Row covers can be purchased in widths ranging 3-60 feet and in lengths 20-2,550 feet. Wider covers are more labor efficient because they have less edge to bury per covered area - but don't try to lay them in a strong wind!

Weed control. Watch for weed growth under the cover because they provide a good environment for weeds too. Covers can be rolled to the edge of the bed for cultivation or herbicide application, and then replaced.

Storage. Row covers should be stored away from direct sunlight as soon as they are removed from the field. While many have been treated to reduce UV degradation, they will last longer if unnecessary UV exposure is prevented. Fold or roll covers in a systematic way so they can be carefully unfolded for next year's use. 

Insect control. Some insects overwinter in the soil where the crop was grown, and emerge in the next spring. In such cases, only use row covers on rotated fields. Also, seal the edges of the cover immediately after installation. If the cover is removed for cultivation, it should be done when insects are less active, such as on a cloudy day or in the morning.

Insects That Can be controlled by Row Covers

Cabbage root maggot fly. This pest is a concern in spring or fall crucifer crops. Pupae overwinter in the soil wherever they fed on fall brassicas. First generation adults fly from April to May and lay eggs at the base of the crop stems. Maggots feed on roots and kill early cole crop seedlings. Immediately after planting, place spunbonded row covers in the field and seal the edges to keep cabbage maggots out. It is important to rotate crops as pupae can overwinter in the soil and flies may emerge under the row covers and damage the crop. 

Flea beetles. There are many different species of flea beetles, each with a specific host crop. Because they typically spend the winter as adults around field edges, they can be effectively excluded by row covers if covers are in place soon after planting. Crucifer and striped flea beetles are tiny, black or striped beetles which cause shot-hole feeding patterns on any of the cabbage family crops. Covers can be used with spring or fall transplants, or all summer on direct-seeded crops, but are too hot for transplants in midsummer. Potato flea beetle causes similar damage to eggplant, tomato, and potato. Corn flea beetles cause feeding damage but are primarily a concern because they vector Steward's wilt. Excluding beetles with row covers prevents infection of young corn plants.

Spinach leafminer and Beet leafminer. These are pests of spring spinach, beets, and chard. The adult black fly emerges from overwintering sites in the soil and lays small eggs in the underside of leaves. Maggots tunnel inside the leaf, making unsightly pathways that render greens unmarketable. Row covers prevent flies from laying eggs on the leaves.

Striped cucumber beetle. This is a pest of cucumber, melons, summer squash, winter squash, and pumpkins. Row covers prevent feeding damage and transmission of bacterial wilt vectored by the beetle. Remove when flowers appear to allow for pollination by bees.

European corn borer. Adults emerge in late May or early June and lay eggs on corn. If row cover is left on into mid- to late June, after flight is peaked, it provides excellent protection to corn. If removed just as flight starts (e.g., first week in June) the larger, healthy corn that was covered may be just as infested as corn that was never covered. Row covers can be left on until tassel if enough slack is left for 3 to 4 feet of stalk growth.

Colorado potato beetle. This insect moves into potatoes and eggplant in late May and early June. Row covers should be removed before tuber initiation, which usually coincides with flowering, to prevent excessive heat.

Potato leafhoppers (PLH). Adults migrate from southern states where they overwinter. Adults usually arrive, reproduce and damage beans, potatoes and sometimes eggplants in June and July, but may last until September. Feeding causes a symptom known as hopper burn, where tips and edges of leaves begin to yellow, curl and die back. Adults and nymphs hide on the underside of leaves. Row covers can be used on beans from emergence until bud stage or the start of bloom. If removed for bloom, damage can be avoided and yields maintained. Lightweight row covers can also be used on potatoes to exclude PLH, flea beetles and Colorado potato beetles.

High Tunnels

High tunnels are greenhouses without permanent foundations that are used to extend the growing season and enhance the environment for crop production. 

 

Site Selection

Avoid sites with inconvenient access, excessive water, poor quality soil, high winds, or low light levels. Ideally tunnels have year-round access, even when crops are not being grown, to allow for snow removal and other maintenance. Existing or potential access to irrigation water is essential, and access to electricity is desirable for inflation fans and mechanical air movement. Some growers have made use of micro-solar power systems to support these loads. It’s desirable to have good access roads and be close to wash/pack facilities. When siting your first tunnel(s) keep in mind future tunnel locations, so that your “build out” over the years allows for efficient access, materials handling and potential for multi-tunnel heating systems, etc.

The site’s topography should allow for drainage of “worst case” storm water and snow melt away from tunnels. A relatively level site is important to minimize structural stress on the tunnel due to uneven snow load. Moderately breezy sites can be helpful for passive ventilation, but high-wind sites create risk of damage to structure and/or plastic covering. TTrees can provide a windbreak but consider their future height when locating tunnels to avoid shading. Also note that dense hedge rows or locations too close to wooded areas can reduce passive ventilation.   

Tunnels should be slightly elevated compared to the surrounding soil in order to allow water running off the cover and drain away from the interior, and to allow snow melt to move away from the tunnel when the ground is frozen. On some sites it is advisable to create a raised pad for tunnels. Some growers install tile drainage, French drains, or curtain drains along the inside or outside of tunnels to carry excess water away from growing areas. Water running through/under a tunnel takes away soil heat, prevents good root growth, and can create muddy working conditions. Orienting tunnels along east-west axis provides optimal light for winter production, and a north-south axis is best to avoid shading inside the tunnel in other seasons, though most crops will have more light than they can use in the summer.  If using primarily passive ventilation in a low wind site, it may also be worth considering the direction of the prevailing wind when orienting the tunnel.

Construction. Do not skimp on the structural integrity of tunnels, as this can lead to collapse in bad weather. Plan for extreme snow and wind. Gothic style tunnels will shed snow better than Quonset hut style structures. Well-set ground posts, cross-ties, and other features that anchor the tunnel and keep it rigid are essential. Doors and vents should close securely to prevent winds from opening them in storms and seal well to help retain heat. It is advisable to have a plan to lower and secure roll up sides for the winter or during high winds. When building a tunnel, avoid driving equipment over future growing areas, as this can create compaction. Installing large doors in end walls or having removable / roll-up end covers to allow for tractor access can make tillage and addition of bulk soil amendments easier than with small equipment. Head houses or other structures make sense for storing tools and equipment, seed, and potting soil, rather than taking up valuable growing space in the tunnel.

Zoning and codes. Before you build, contact your state and local agencies to find out about regulations and tax policies for high tunnels. Some states and towns may require building permits; setback requirements and building codes vary among municipalities. Some consider tunnels to be real property (subject to tax) and others do not. It may be helpful to be very clear with local officials that the structure is not permanent and is used for producing agricultural crops.

Soil Quality and Fertility

As in the field, tunnel crop production will benefit from deep, well-drained, fertile soil that is not compacted. On most sites, soil amendments such as compost, peat moss or coir will be desirable to increase the organic matter level to optimize tunnel production. Lime and nutrients should be added based on soil tests prior to production. On sites with poor native soil, compaction and/or drainage problems, soil can be imported either into the entire tunnel, raised beds, containers or by using ‘grow-bags’ of pre-fabricated media.

Since tunnel soils are not exposed to regular leaching from rainfall, soluble salt levels can build up over time negatively affecting plant growth. Salts dissolve into ions in soil solution and come from the application of fertilizers and composts or manures. Crops remove some of these salts in their tissues, but the excess remains in tunnel soils, unlike in the field. Strawberry, green beans, and certain herbs are very sensitive to salts, but even tolerant crops such as tomato and spinach can show reduced vigor with very high levels. Salts tend to accumulate especially in the top few inches of soil, as they move upwards with evaporation. This can affect germination of winter crops while transplanted crops such as tomato may be more tolerant to high salt levels.  Deep tilling will remix those salts into the soil profile. Salt injury can be exacerbated if soils are allowed to dry out. Excessive salts can be reduced by diluting with the addition of peat moss, coir or topsoil. Irrigating with a large amount of water can move salts down in the soil profile, but is often impractical. Removing the plastic cover over winter is perhaps the easiest way to leach salts out of the root zone. Soil tests can be used monitor the buildup of salts over time.

Because high tunnels specifically and protected culture more generally increase heat in the soil and air, the season is extended and yields are increased. This leads to obvious questions about whether soil fertility information from field crop research can be used to effectively guide high tunnel crop fertilizer application. Tunnel tomato fertility recommendations have been updated based on yield goals. While similar updates for other tunnel crops are not available, soil tests, tissue tests and observations of nutrient deficiencies can help fine tune nutrient applications in tunnels.

Ventilation

Air exchange in tunnels is essential to avoid high temperature, high humidity, and low CO2 in tunnels, leading to plant stress or disease. Passive ventilation using roll-up sides is common in tunnels, though some tunnels use mechanical ventilation with fans to pull air through the tunnel. Generally, you must pick one or the other or use them at different times. Fans pull from the point of least resistance, so running an end-wall fan with the sides rolled up simply pulls air from around the corner, not from the other end of the tunnel. When sizing fans for ventilation the basic rules of thumb are 8 CFM/ft2 (of growing space) for summer cooling and 2 CFM/ft2 to remove humidity during cooler months. Note that this guidance is for peak ventilation needs.  Staged fans (e.g., one small, one large) or variable speed fan controls can help moderate the ventilation for various times of the year.
Passive ventilation is less than ideal in locations where tunnels are crowded together, there are lots with trees or other significant wind breaks, or in calm sites with little wind. A dense crop canopy later in the growing season also reduces passive ventilation.  

Installing a ridge-vent (along the top peak of the tunnel roof) will greatly increase the effectiveness of passive ventilation, though these can be costly and they make installation of plastic cover more complicated. Some growers who have ridge vents have installed “cat walks” to ease maintenance.  These can make plastic replacement and repairs easier. Gable vents high up on end walls can also improve ventilation by acting as outlets for warm humid air in warmer seasons and by allowing for low volume ventilation in colder weather. A 24″x24″ gable vent on each end wall is recommended for a 30′x96′ tunnel. These can be made of plywood and manually operated with hinges, ropes or cables and tie-downs. If using a louvered vent, be sure it has a flanged seal to close against. Thermostatic wax cylinder actuators may also be used which require no electricity, are relatively inexpensive and are passively controlled by the wax cylinder based on temperature.

HAF Fans. Horizontal air flow (HAF) fans are hung from the inside horizontal structural tubing to mix the air inside a tunnel to create consistent growing conditions, they don’t improve ventilation.  They are for circulating and mixing the air inside the tunnel. When installed and used properly, they ensure that plants and any control sensors are seeing the “average” conditions of the space. The first fan should be placed about 10′-15′ from one end wall to pick up the air that is coming around the corner from the other side. Subsequent fans should be located 40′-50′ apart to keep the air mass moving. In a 30′x100′ greenhouse, four fans are required, and the total fan capacity should be 6,000 CFM (2 CFM/ft2). The “empty” corner, where there is no fan can sometimes become a spot without air flow. Check to make sure you can feel air flow in all locations in the house.  You may have to add fans or reorient the ones on the end to promote adequate mixing flow. If a tall crop such as tomatoes is grown or if there are hanging baskets, a slightly greater capacity is needed to overcome the additional air flow resistance. Small, 1/10-1/15 horsepower circulating fans work well in providing the air movement needed. A permanent split capacitor motor can save as much as one-third the electricity of the more common shaded pole motor. Some growers have used inexpensive, simple box fans and just plan for frequent replacement. High efficiency vane-axial fans can increase the “throw” of each HAF fan meaning you need fewer fans to provide the same mixing flow.
 

Tunnel Covering

Typical high tunnel covering is greenhouse grade 6 mil polyethylene rated for 4-6 years. Using two layers, separated by air blown between the layers, reduces heat loss during cold season production and provides stability under windy conditions, reducing damage to the plastic. Solid plastic “spacers” are available to separate two layers of plastic in locations without electricity.  Some greenhouse plastics have additives to enhance durability and performance. UV stabilizers are essential to slow degradation of plastic. Anti-fog and anti-drip surfactants make water condense and run down to the sides of the structure, rather than bead and drop on the plants below. IR radiation-blocking additives reduce heat loss at night. UV-absorbing films have the potential to suppress certain insects and diseases. In summer, plastic may be covered with shade cloth to reduce light intensity and temperature. Shade cloth is rated by the percent of light blocked. Whitewash is also used by some growers to help keep tunnels cool in summer. 

Heating

When it’s cold outside, growers may want to heat the air and/or soil inside a tunnel, and this can be done using permanent heating systems, or emergency systems for coping with unusual conditions. Whatever system is used, a temperature warning system is important to provide notification when heating (or cooling) is urgently needed. To determine what size heater is needed, one must calculate the heat loss when a certain minimum temperature is desired inside the tunnel when there is a certain outside temperature. More information on heating, ventilation, and other engineering issues can be found at the University of Massachusetts greenhouse and floriculture web site and on the University of Vermont Extension agricultural engineering blog.

Irrigation

Water must be provided to replace that lost by evapotranspiration (ET), the combination of soil surface evaporation and water loss from plant leaves. Drip irrigation is an efficient way to deliver water and nutrients in a tunnel, while keeping the foliage dry, which reduces disease pressure. Drip tape is usually 8-10 mil thickness and is laid on the surface or buried an inch or two. Flow rates of drip tapes vary, a medium–flow tape provide 0.5 gpm per 100 feet. High-flow tape with 1.0 gpm flow is useful to prevent clogging and reduce irrigation time. Drip lines should be spaced on or under the soil surface to assure that the entire bed or row is wetted. Light-textured soils have less capillary movement of water than heavier soils, so in these soils, more drip lines may be needed to prevent dry areas in the bed. Many systems are available to add soluble fertilizer to irrigation water. Fertigation is a good way to provide plants with the nutrients they need over the season, or to supplement fertilizers applied at planting. Irrigation water quality should be tested. Water with high pH and high alkalinity may lead to increased soil pH over time.

A mature crop of tomatoes may require 2.5 quarts of water per plant per day, whereas winter greens may grow well only on existing soil moisture, and if irrigated, may develop disease. Determining the optimal amount and timing of irrigation is complicated since it depends on the crop, its stage of growth, soil texture, sunlight, temperature and humidity. Use of soil moisture sensors placed at several locations and depths in each tunnel, combined with irrigation and crop performance records, can help determine best practices on your farm. 

Pest Management

The tunnel environment differs from the field, so the type and timing of insects and diseases also differs. For example, spider mites and aphids are more frequent pest in tunnels than outdoors, and foliar diseases in tunnels are typically due to humidity levels. The use of biological insect controls is more practical in tunnels than outdoors due to the (at least partly) enclosed space, high crop value, and extensive information developed for many crops. See the University of Vermont’s high tunnel pest management web site for more information. Maintaining the area around the perimeter of the tunnel with mowing and trimming is a passive way of minimizing mammalian pests by reducing cover.

Pesticides. Outdoors, pesticide residues break down after application by exposure to ultraviolet radiation and rainfall. Inside tunnels, plastic coverings reduce U/V and rain, and as a result, pesticides break down differently. Each state’s pesticide regulatory agencies may have different interpretations of whether high tunnels are considered open fields or greenhouses, however it is safest to consider a high tunnel a greenhouse from the perspective of pesticide labels. The label may 1) specifically state that the product may be used in greenhouses and may provide different guidelines for greenhouse and outdoor use, 2) specifically state that the product may not be used in greenhouses, or 3) may not mention greenhouse use at all. The Environmental Protection Agency’s current position is that a label does not have to specify greenhouse as a site, provided the crop is on the label, in order to use the product in a greenhouse. If the label has multiple sections, and one of those sections is for greenhouse application, then the label must be followed explicitly for greenhouses with no exceptions. The rate for outdoor applications on those crops is for outdoor use ONLY and CANNOT be used for those crops in the greenhouse, since those crops were not included in the greenhouse section of the label. Using a pesticide inside a greenhouse where the label does not mention greenhouse use can increase risks to workers or plants. Also, when using a fumigant or smoke generator for an entire greenhouse, every crop in the greenhouse must be listed on the product label. We advise against applying a product in high tunnels unless the label specifically allows its use in greenhouses.

Estimating Vegetable Yields

Yields vary a great deal due to climate, growing conditions, soil quality, and farm management.  To estimate yield in a consistent manner, one can harvest 10' of row at several locations in the field. Multiply the average yield (lb) per 10' of row times the following row spacing factors to convert the sample yields to lb/A. See Table 14 and Table 15.

Table 14: Estimating Vegetable Yields

Row Spacing in Inches Multiply By
12 4360
15 3480
18 2900
20 2610
21 2490
24 2180
30 1740
36 1450
42 1240
48 1090
56 930
60 870

 

Table 15: Approximate Yields

Adapted from Knott's Vegetable Grower Handbook, The New England Vegetable Growers Yield Guide Table, United Fresh Fruit Market Containers and Weights, The Boston Fresh Vegetable Wholesale Market and Arrivals Report, and the USDA-National Agricultural  Statisitics Service New England Vegetable and Strawberry Report (2014-2018).

Abbreviations for Vegetable Yield Table

  • bun. = bunch
  • ct. = count
  • qt. = quart
  • bu. = bushel
  • doz. = dozen
  • lb. = pound
  • pt. = pint
  • wt. = weight
      YIELD PER ACRE*    
Vegetable

CONTAINER OR UNIT

LOW

GOOD

EXCELLENT

NEW ENGLAND
5-YEAR AVERAGE
Asparagus

20 lb box

1,600 lb

2,000 lb

4,000 lb

1,320 lb
Basil

24 ct; 12 lb

3,000 lb

4,000 lb

6,000 lb

-
Beans, snap

1 1/9 bu box; 20 lb

4,000 lb

8,000 lb

10,000 lb

2,960 lb
Beets, red bunched

24 ct; 40 lb box

20,000 lb

24,000 lb

30,000 lb

7,140 lb
Broccoli

14 ct bun; 20 lb box

5,000 lb

8,000 lb

10,000 lb

-
Cabbage

1 2/3 bu box; 50 lb

20,000 lb

30,000 lb

40,000 lb

13,900 lb
Canteloupe / Muskmelon

12-16 ct 1 1/9 bu box; 40 lb

8,000 lb

16,000 lb

20,000 lb

7,900 lb
Carrots

50 lb bag

20,000 lb

26,000 lb

30,000 lb

11,120 lb
Cauliflower

12 ct 1 1/9 box; 25 lb

8,000 lb

14,000 lb

20,000 lb

4,220 lb
Corn, sweet

5 doz bags; 50 lb

750 doz

1,000 doz

1,500 doz

744 doz
Cucumber

1 1/9 bu box; 40 lb

12,000 lb

20,000 lb

26,000 lb

9,660 lb
Eggplant

1 1/9 bu box; 25 lb

16,000 lb

20,000 lb

24,000 lb

8,310 lb
Endive/Escarole

24 ct 1 1/9 bu box; 20 lb

21,000 lb

23,000 lb

26,000 lb

-
Garlic

1/2 bu box; 10 lb

2,000 lb

4,000 lb

6,000 lb

2,120 lb
Kale/Collards

24 ct bun 1 3/4 bu box; 20 lb

10,000 lb

12,000 lb

18,000 lb

11,150 lb
Kohlrabi

25 lb bags

14,000 lb

20,000 lb

30,000 lb

-
Leeks

12 ct bun 3/4 bu box; 15 lb

28,000 lb

32,000 lb

36,000 lb

-
Lettuce, leaf

24 ct 1 1/2 bu box; 25 lb

26,000 lb

29,000 lb

33,000 lb

7,160 lb
Lettuce, head and romaine

24 ct 1 3/4 bu box; 35 lb

36,000 lb

40,000 lb

46,000 lb

8,520 lb
Onions, dry bulb

50 lb bags

30,000 lb

40,000 lb

50,000 lb

11,220 lb
Onions, green bunch

24 ct bun 1/2 bu box; 10 lb

16,000 lb

18,000 lb

20,000 lb

5,740 lb
Parsley

30 ct bun 1/2 bu box; 12 lb

12,000 lb

16,000 lb

20,000 lb

-
Parsnip

25 lb bag

16,000 lb

20,000 lb

26,000 lb

-
Pea, snap

varies

3,000 lb

6,000 lb

8,000 lb

2,140 lb
Pea, pod

varies

6,000 lb

9,000 lb

14,000 lb

-
Pepper, bell

1 1/9 bu box; 25 lb

23,000 lb

30,000 lb

37,000 lb

10,000 lb
Potato, Irish

50 lb bag

15,000 lb

25,000 lb

35,000 lb

29,300 lb 
Potato, fingerling

5 lb bag

10,000 lb

15,000 lb

20,000 lb

-
Pumpkin

20 bu bin; 1,000 lb

30,000 lb

36,000 lb

40,000 lb

10,260 lb
Radish

24 ct bun 1/2 bu box; 10 lb

4,000 lb

6,000 lb

10,000 lb

-
Rhubarb

3/4 bu box; 20 lb

10,000 lb

14,000 lb

18,000 lb

-
Rutabaga

25 lb bag

30,000 lb

36,000 lb

40,000 lb

17,400 lb
Spinach

loose 1 1/9 bu box; 10 lb

8,000 lb

12,000 lb

14,000 lb

4,180 lb
Squash, summer

1/2 bu box; 20 lb

20,000 lb

30,000 lb

40,000 lb

8,840 lb
Squash, winter

1 1/9 bu box; 40 lb

24,000 lb

30,000 lb

40,000 lb

9,620 lb
Sweet Potato

per lb - retail

12,000 lb

15,000 lb

25,000 lb

-
Strawberry

8 qt flat; 12 lb

6,000 lb

10,000 lb

16,000 lb

3,747 LB
Tomato, field

1 1/9 bu box; 20 lb

20,000 lb

30,000 lb

40,000 lb

10,600 lb
Tomato, greenhouse

10 lb box

3 lb/ft2

4 lb/ft2

6 lb/ft2

-
Turnip

25 lb bag

20,000 lb

24,000 lb

30,000 lb

-
Watermelon

1 3/4 bu box; 40 lb

12,000 lb

20,000 lb

24,000 lb

10,800 lb

NOTE: To convert yield per acre to yield per 100 feet of row:  multiply yield per acre by the number of feet between rows and divide by 4356.

* Yields vary depending on soil quality, weather conditions, farm management, location, etc. Low, Good and Excellent yields are based on national data, while 5-year averages (2017-2021) are from the USDA National Agricultural Statistics Service New England Vegetable Report and the USDA NASS New England Berries, Tree Fruit & Grapes Report

Postharvest Handling and Storage

Harvested vegetables are living things that carry on the process of respiration and other biological and chemical processes. How produce is handled after harvest will directly affect quality characteristics such as appearance, flavor, texture and nutritional value. Attention to postharvest quality can increase repeat sales and support higher prices.

Control of postharvest quality essentially comes down to limiting respiration rate (lowering temperature), controlling water loss (maintaining proper relative humidity), minimizing physical damage to the product (harvesting and handling with care), and avoiding contamination (handling, washing and storing appropriately).

Limiting Respiration

Respiration is a temperature dependent biochemical process that converts carbon in plant tissue (mainly sugars) to carbon dioxide (CO2) and water (H2O) while producing some heat. Rates of respiration vary by the crop (see Gross 2016, Table - p. 7 and pp. 68-75 in References at the end of this chapter), and should be taken into account when sizing cooling equipment. Fortunately, we can significantly reduce respiration, and therefore maintain high product quality, by reducing product temperature (precooling) and keeping it low (holding or storage cooling).  This concept is known as establishing the “cold chain”; a chain of reduced temperature that connects the field to the consumer ensuring the highest quality produce possible by minimizing respiration.

From the moment of harvest, product quality will deteriorate.  Intentional precooling of produce directly after harvest helps quickly reduce the rate of respiration and initiates the cold chain.  Examples of precooling include scheduling harvest activities at cooler times of day, shading harvested product in the field prior to transport, forced air cooling through the packed product with refrigeration, hydrocooling with cool water, and vacuum cooling via evaporation. Once cooled to storage temperature, reliable, refrigerated storage is necessary to maintain high quality.

It is important to note that not all crops can be cooled to the same temperature without resulting in cold or freeze injury and some crops are sensitive to the method of cooling.  Crops have different susceptibility to chilling or freeze injury depending on their physiology.  Good guidance is available (see Gross 2016, p 62-67) and is summarized in Table 16 of this guide.  Common precooling methods are also noted in Table 16. Additionally, a computer based crop storage planner is available for determining appropriate grouping of your crops and estimating overall respiration load (see Callahan 2016). Chilling injury is also an important consideration when considering particularly sensitive Fall harvested crops and the possibility of lower nighttime temperatures, e.g. winter squash. Notes on chilling injury guidance for these crops are provided in the appropriate crop chapter and in the references above.

Controlling Water Loss

The control of water loss requires careful attention to relative humidity (RH) of the air surrounding stored product in addition to temperature. RH is a measure of the amount of water vapor in air compared the maximum amount that can be saturated in that air at a given temperature.  Most, but not all, crops are ideally stored at higher RH to prevent water evaporation into the air leading to water loss.  The loss of water reduces the weight of the crop and also can lead to lower quality and poor appearance.

Some crops, such as onions, garlic and winter squash, are purposefully “cured” or dried resulting in drier outer skin and curing harvest wounds to allow long term storage. Because this results in a paper-like layer, these crops are generally stored at lower RH to prevent development of postharvest disease such as molds and fungi on this outer skin.  Other than these examples, most crops are best stored at 90%-95% RH with specific guidance provide in Table 16, in the crop storage planner noted above, and in the literature (see Gross 2016).

Minimizing Physical Damage

Generally speaking, produce crops live a very gentle life until harvested.  Starting with harvest, produce is moved and handled for the first time and, typically, many times after. With each movement there is a risk of physical damage.  Even if the damage is not obvious, it can result in bruising or other damage that becomes evident later and can led to postharvest disease and pathogens which are encouraged by damaged cell tissue.  Even during harvest, crops can suffer “harvester blight.”  For the majority of crops, gentle handling, crates with smooth and clean surfaces, and conveyance with elastic and soft belts and rollers should be used.

Avoiding Contamination

Sorting and culling are also important practices at this stage. As the saying goes, “one bad apple can spoil the bunch”.  Sorting allows for different sizes and grades of product to be stored and sold separately and culling can separate damaged or lower quality product from the main lot for sale, rescue donation or compost depending on the defect.  The removal of obviously damaged product from the lot helps minimize cross contamination postharvest pathogens to a larger portion of the population.

Produce can be rinsed to remove soil and debris, and often a sanitizer is added to the rinse water to prevent cross-contamination of plant and human pathogens from one item of produce to another in the same batch (see the following references: LaBorde, Samuels and Stivers 2016, Bihn et al. 2014).

Once packed and ready for storage or transport, care should be taken to avoid contamination of product with other contaminants such as foreign matter and unintentional water such as condensate from refrigeration systems.

References

Gross, Kenneth C., Chien Yi Wang, and Mikal Saltveit, eds. 2016. The Commercial Storage of Fruits, Vegetables, and Florist and Nursery Stocks. Agriculture Handbook 66, U.S. Department of Agriculture, Agricultural Research Service, Washington, DC. Available at https://www.ars.usda.gov/ARSUserFiles/oc/np/CommercialStorage/CommercialStorage.pdf. Confirmed July 25, 2022.
Callahan, Christopher W. 2016. Crop Storage Planning Tool. UVM Extension. Available online. http://blog.uvm.edu/cwcallah/2016/01/21/new-crop-storage-planning-tool/. Confirmed July 25, 2022.
Bihn, E., Schermann, M. A., Wszelaki, A. L., Wall, G. L., and Amundson, S. K. 2014. On-Farm Decision Tree Project: Postharvest Water. National Good Agricultural Practices Program.  Available online. https://gaps.cornell.edu/educational-materials/decision-trees/postharvest-water. Confirmed July 25, 2022.
LaBorde, L., Samuels, R. and Stivers, L. 2016. Video Series: Using Sanitizers in Washwater. Available online. http://extension.psu.edu/food/safety/farm/gaps/video-series-washwater-sanitation.  Confirmed July 25, 2022.

Table 16: Handling Produce for Higher Quality and Longer Market Life

Information on optimum temperatures, relative humidity and storage life was adapted from USDA Handbook 66 and modified by experience under northeastern conditions.

  Recommended Cooling Methods1 Important Handling Factors
Vegetable Crop Forced Air or Room Cooling Hydro-Cooling Package Ice or Liquid Icing Vacuum Cooling Transit Icing2 Recommended Transit & Storage Temp. °F3 Recommended Transit & Storage Rel. Humidity, % Expected Marketable Life Under Best Conditons Sensitivity to Chilling Injury4
Asparagus   +   + N 32-36 95 1-2 weeks L
Basil +       N 46-50 90-95 4-7 days H
Beans, lima  + +     N 38-42 90-95 7-10 days M
   snap + +     N 40-45 90-95 7-10 days M
Beets, bunched   +     R 32   1-2 weeks I
Broccoli     +   E 32 90-95 1-2 weeks I
Brussels sprouts + + + + R 32 90-95 3-5 weeks I
Cabbage +       N 32 90-95 3-6 weeks I
Cabbage, Chinese +   + + R 32 90-95 4-8 weeks I
Carrots, Topped +   +   N 32 90-95 6-7 months L
Carrots, bunched +   +   E 32 90-95 1 month I
Cauliflower +   + + R 32 90-95 2-4 weeks I
Celery   +     R 32 90-95 2-3 weeks I
Collards & kale   + +   R 32 90-95 1-2 weeks I
Cucumbers + +     N 50 90-95 1-2 weeks H
Eggplant +       N 50 90-95 1 week H
Endive & escarole       + R 32 90-95 2-3 weeks I
Kohlrabi + + +   R 32 90-95 2-4 weeks I
Horseradish +       N 30-32 90-95 1 year I
Leeks   + + + R 32 90-95 1-3 months I
Lettuce, crisphead       + N 32-36 95 2-3 weeks I
   leaf & bibb     + + R 32-36 95 1 week I
   romaine       + R 32-36 95 1-2 weeks I
Muskmelon,    3/4 slip +   +   R 36-40 85-90 1-2 weeks M
   full slip +   +   R 32-36 85-90 4-7 days M
Okra   +     N 45-50 95 1 week VH
Onion, dry         N 32 65-70 1-8 months I
   green   + +   N 32 90-95 7-10 days I
Parsley   + +   E 32 95 1-2 months I
Parsnips +       N 32 90-95 2-6 months I
Peas   + +   E 32 90-95 1-2 weeks I
Peppers +     + N 45-50 90-95 2-3 weeks M
Potatoes, early +       N 40 90 2-4 months L
   late +       N 40-45 90 5-8 months L
Pumpkins         N 50-55 70-75 2-3 months H
Radishes, bunched   + +   E 32 95 1-2 weeks L
Rhubarb   + +   R 32 95 3-4 weeks I
Rutabagas +       N 32 95 2-4 months I
Spinach   + + + E 32 90-95 7-10 days I
Squash, summer + +     N 50 90-95 4-7 days H
   winter +       N 55-60 50-75 2-6 months M
Strawberries +       N 32 95 1 week I
Sweet potatoes +       N 55-60 85-90 3-5 months VH
Sweet corn + + +   E 32 90-95 5-7 days L
Tomatoes, green +       N 55-70 85-90 1-3 weeks H
   pink +       N 50-60 85-90 5-10 days M
   ripe +       N 40-45 85-90 4-7 days M
Turnips +       N 32 95 4-5 weeks I
Turnip/mustard tops   + + + E 32 90-95 1-2 weeks I
Watermelons +       N 45-50 85-90 3-4 weeks M

1 Cooling Method: + = cooling method is suitable for the crop.

2 Transit Icing: The importance of transit icing depends on time in transit, transit conditions, and outside temperature. N = not recommended, R = recommended, and E = essential.

3 Accurate temperature control is essential; do not allow temp to fall below 32°F

4 Sensitivity to Chilling Injury: I = insensitive, L = low sensitivity, M = medium sensitivity, H = high sensitivity, and VH = very high sensitivity.

 

Produce Safety

While the United States enjoys one of the safest food supplies in the world, the Centers for Disease Control and Prevention (CDC) estimates that one in six people get sick from a foodborne illness each year, with fresh produce accounting for nearly half of these illnesses. Produce encounters many opportunities for microbial contamination with fecal pathogens during growing, harvest, and distribution, whether through direct exposure to manure or through contact with contaminated water, soil, containers, equipment, or workers. Fresh produce is frequently eaten raw and so may not undergo heating or other processing that would kill pathogenic organisms. Preventing produce from coming into contact with these organisms is the best way to prevent foodborne illness related to fresh produce.

Good agricultural practices, or GAPs, are those practices that help to reduce exposure of produce to disease-causing microbes. In New England, buyers are requesting and, in some cases, requiring that growers become certified by a 3rd-party audit program to demonstrate that they are following GAPs. Examples of these programs include the USDA’s GAP and Harmonized GAP audit programs, Commonwealth Quality (CQP) in Massachusetts and Community Accreditation for Produce Safety (CAPS) in Vermont. 

In 2011, the Food & Drug Administration passed the Food Safety Modernization Act (FSMA), which focuses on preventing rather than responding to contamination within the food supply. It consists of seven rules, including the Produce Safety Rule, which sets standards for the growing, harvesting, packing, and holding of produce for human consumption. This rule is the one most likely to impact fruit and vegetable growers. It became final in January 2016. Compliance was phased in for affected growers, depending on their annual produce and food sales.  This phasing in process began in 2018, but some portions of the rule are under review. If you are unsure where your farm falls under this rule visit UNH Extension’s online tool (link is external) or contact your local Extension representative. 

FSMA’s Produce Safety Rule is enforced at the state level, and each of the six New England states has their own enforcement models. Responsible agencies are listed below. Contact the agency in your state for more information on food safety regulations and best practices, and your responsibilities under FSMA:

Connecticut: Connecticut Department of Agriculture
Maine: Maine Department of Agriculture, Conservation and Forestry 
Massachusetts: Massachusetts Department of Agricultural Resources
New Hampshire: New Hampshire Department of Agriculture, Markets, and Food
Rhode Island: Rhode Island Department of Environmental Management
Vermont: Vermont Agency of Agriculture, Food & Markets

Efforts to prevent contamination of produce should be focused on the following key hazard areas. Be aware that FSMA’s Produce Rule sets specific requirements for covered farms with respect to water quality and testing, worker training, and other aspects of production and handling. For all other farms, the rules and information about hazards can serve as best management practice recommendations. Refer to the FDA’s Final Rule on Produce Safety or contact your state Extension or responsible regulatory agency for more information. 

Agricultural Water

Water is used in many ways on a farm and is a primary vehicle for the movement of pathogens. Agricultural water can be divided into two groups: production water and postharvest water. Production water is water that contacts the harvestable portion of a crop and includes any water used for irrigation, crop sprays, or frost protection. Postharvest water is any water used during and after harvest and includes water used for produce washing, commodity movement, cooling, ice making, postharvest fungicide applications, handwashing, and cleaning and sanitizing of food contact surfaces. 

Consider the source of your agricultural water and how the water will be used in order to manage potential contamination. Surface water, including rivers, streams, lakes, ponds, man-made reservoirs, and any other water source that is open to the environment, is subject to the highest risk. Water quality from surface water can vary greatly between sites and over time. Some major contamination risks include wildlife, water runoff from upstream livestock operations, and wastewater discharge. Untreated surface water should never be used for postharvest applications and should be monitored carefully when used as production water. Ground water, or well water, poses less risk than surface water for agricultural uses, however hazards such as cracked well casings and leaky septic systems increase the risk that ground water can become contaminated. Public water supplies are monitored and treated by municipalities and therefore pose the least risk, although water still may become contaminated within your distribution system. It is important to be aware of the risks to the microbial quality of agricultural water and to keep contaminated water from contacting produce. 

Routinely test agricultural water for generic E. coli to get an indication of its microbial quality. Test both at the source and at the output to test for contamination within the distribution system. Production water should be below 126 CFU/100ml for generic E. coli and postharvest water should be potable or have 0 CFU/100ml. Keep potentially high risk water from contacting the harvestable portion of a crop. Example risk reduction strategies are to switch from overhead irrigation to drip irrigation, or for postharvest applications, use single-pass water (e.g. spray from a hose, conveyer, or barrel washer) instead of recirculated or batch water (e.g., from a recirculating conveyor or dunk tank). Recirculating water can become contaminated and present a cross-contamination risk, and if it is used it should be changed frequently enough that it remains of adequate sanitary quality for its intended use. Sanitizers labeled for use in produce wash systems can help reduce the risk of cross-contamination in recirculated or batch water and can help reduce the build-up of microbes and biofilms on food contact surfaces. Be aware, though, that sanitizers are pesticides and must be labeled for their intended use and handled and monitored carefully while following your state’s pesticide regulations. In particular, some sanitizers are labeled for use in produce wash water while others are labeled for use on food contact surfaces. In some cases the same product can be used for either purpose, but the mixing instructions are different.

Worker Health, Hygiene, & Training

People can easily move pathogens around the farm and onto produce through dirty hands or clothing. Good hygiene and regular, proper handwashing can prevent produce contamination. Make clean, well-stocked, readily accessible toilets and handwashing stations available to workers and farm visitors at all times. Ensure that anyone working around produce maintains personal cleanliness and that all employees know how and when to wash their hands. 

Educate your employees with the information they need for their particular job regarding food safety and empower them to make informed decisions about contamination risks. An employee who only harvests produce will need different information than an employee who works full time in the wash/pack house. Ensure that your employees know how to identify potentially contaminated produce or food contact surfaces and know what to do if produce becomes contaminated or if they or another employee is sick.

Postharvest Handling & Sanitation

Good housekeeping in wash and pack areas can help prevent produce from becoming contaminated. Keep postharvest areas clean and organized and encourage workflow that reduces overlap between washed and unwashed produce, containers and equipment. Keep produce handling areas separate from other farm activities such as tractor repairs, pesticide mixing, or employee break areas. Do not store sanitizers where they could spill on produce.  Bacteria thrive and multiply in water, so allow equipment to dry and minimize standing water with good drainage and/or by routinely clearing pooled water. If your packing area is outside, be sure that area drains well. A gravel pad can help with drainage and soil splash. Keep pests from entering produce wash, pack, and storage areas and establish a pest management program, if necessary. 

In addition to general cleanliness, it is important to know how to clean and, when necessary, sanitize tools, equipment, and surfaces effectively. While cleaning and sanitizing should be focused on food contact surfaces—any surface that comes into physical contact with produce—you should also clean “secondary” surfaces that may indirectly contact food or food contact surfaces. 

Cleaning and sanitizing refer to separate actions. Cleaning is the physical removal of dirt and organic matter from surfaces, using water and a detergent. Sanitizing is the treatment of a cleaned surface to reduce bacterial pathogens to a level considered safe as judged by public health entities. A dirty surface cannot be sanitized—cleaning always comes first. Disinfection is a process used to destroy or irreversibly inactivate bacteria, fungi and viruses, but not necessarily bacterial spores. A disinfectant would typically only be used if a surface were known to be contaminated by blood or other bodily fluids. In that case, after disinfecting with a product labeled for disinfection, and if the surface is a food contact surface it would be rinsed with potable water then sanitized again.  This is because disinfectants are strong and can themselves become a food contaminant if not used according to the label.

Soil Amendments

Food safety risks regarding soil amendments generally involve raw manure, or other untreated animal-based soil amendments. All animal-based soil amendments can contain pathogenic microorganisms if they are not processed in a way that kills such pathogens. If you use composted manure on your farm, you need to ensure that the manure is composted correctly and fully. Otherwise, it should be used as raw manure.

In the fall, if applying manure to land in food production, do so preferably when soils are warm (over 50ºF), non-saturated, and cover-cropped. The rest of the year, incorporate manure whenever possible. Maximize the time between application of manure and harvest—a good guideline is the National Organic Program Standard of a 90-day interval for crops that do not touch the soil and 120 days for crops that do. Keep records of all manure and fertilizer application rates, source, and dates. Avoid planting root or leafy crops if manure is applied in spring. 

Never side-dress food crops with fresh solid manure, slurry manure, manure 'tea' or any mulches containing fresh manure. However, it is ok to side-dress with mature compost. A mature compost is one that has been thoroughly heated, turned several times, and allowed to age for a long enough time that it is virtually odor-free and is not objectionable to handle with bare hands. If you do not have records or certification that compost was properly treated to control pathogens, handle it like raw manure and observe the suggested 90-120 day application interval.

Wildlife, Domesticated Animals, & Land Use

Animals on farms can pose food safety concerns because they can carry certain human pathogens (e.g., Salmonella, Listeria, and E. coli) and can spread those pathogens through fecal matter directly to produce in fields, or indirectly through water sources. Avoid grazing livestock near produce fields and keep pets out of production areas. Assess risks posed by livestock on adjacent land. It is impossible to exclude all wildlife from produce fields, but minimize wild and domestic animal traffic by use of fences, scare devices or other means. Consider berms to prevent runoff entering a produce field. Have a plan for how you will manage contamination when it happens. Never harvest produce that is or that you suspect to be contaminated with animal excrement.

Farm Food Safety Plans & Traceability

Accurate recordkeeping and documentation of practices are essential for ensuring that the risk management strategies described above are done consistently and effectively. Recordkeeping templates are available from the Produce Safety Alliance. A farm food safety plan can help you to compile relevant food safety documents such as risk assessments, standard operating procedures, training information and record keeping logs that can help you  identify areas on your farm that pose the greatest risk and address them. A food safety plan may also be required by buyers or third-party audit programs. Your plan may include a traceability program to help you track your produce one step forward and one step back within the distribution chain in order to quickly respond in the case of a foodborne illness incident. Tracking produce requires the definition of a “lot” or distinct and limited portion of a crop and a code for identifying that lot. Lot codes should be a unique code for the identifying characteristics of a lot—for example, the crop and variety name, field or block of origin, and the harvest and packing date. This code will help you identify a particular lot once it has been sold in case you wish to remove your product from the market for any reason, as well as describe it with important information that may help in the case of an investigation. 

Organic Certification

Federal legislation requires certification of agricultural products that are labeled as organic. Producers whose gross sales of organic products are under $5,000 must know and meet the USDA/National Organic Program Regulations (https://www.ams.usda.gov/rules-regulations/organic), but are not required to seek certification. These small scale producers are encouraged to get certified for marketing benefits. Farms selling more than $5,000 of products labeled as organic must be certified by a certifier that is accredited by the USDA National Organic Program. See below for a list of certifying organizations in New England currently accredited by USDA.

National Organic Standards

Organic agriculture is based on the use of practices and inputs that enhance the physical, biological and chemical aspects of the soil and its ability to sustain crop and animal production in an environmentally safe manner. Natural sources of crop nutrients and cultural practices that build or maintain fertility are required by the National Organic Standards. Organic agriculture relies on cultural practices as much as possible for pest management, but allows natural based pesticides when needed. In general, the use of synthetic substances for pest management is prohibited, although some synthetic materials are allowed and these are noted in Section 205.601 of the USDA National Organic Program Standards.

This Guide includes information on many organic practices and materials approved by the National Organic Program. See information on sources for crop nutrients in the section Guidelines For Organic Fertility Management. Compost use is discussed in the section Fertilizers and Soil Amendments. Approved methods of managing weeds, insects and diseases are noted in the Pest Management section. Organically accepted practices are also included in the specific crop chapters.

Organic Material Review

The grower is responsible for determining whether materials are allowed under organic standards. Sometimes this may be a challenge because some materials labeled as organic by the manufacturer may not actually meet the standards of the National Organic Program or by a third-party organic review organization. Third party review organizations include the Organic Materials Review Institute (OMRI), Washington State Department of Agriculture (WSDA) and California Department of Food and Agriculture (CDFA), all of which are recognized by the USDA National Organic Program as organic material review organizations, though CDFA only reviews fertility inputs. These organizations publish lists of products suitable for certified organic production. These products are generally allowed, but some are regulated and subject to restrictions and may only be allowed for certain production scopes. It is the responsibility of the grower to know the restrictions on, and scope specification of, product use. In some cases, a third party review organization may note that certain formulations of a product are permitted and others are not. The list of substances approved are subject to change. For the most up-to-date lists, visit their web sites at: OMRI, WSDA and/or CDFA. If using a product not on one of these lists, be sure to check with your certifier in advance to be certain that the materials and practices you plan to use are approved by your certifier, and that you understand any restrictions on use. In some cases, application of a material that is not approved for use in organic production could result in land needing to be re-transitioned for a three year period.

When mentioned in tables or in crop chapters, this Guide designates approved organic materials with a superscript OG (OG), which means they were "OMRI listed" as of June 2022, when the materials were reviewed.

Accredited Organic Certifiers in New England

The following is a list of accredited organic certifiers in New England. Note that some certifiers may limit the scope of the certification they offer, for example, some certify crops but not livestock, and some may certify farms only within a certain geographic area. 

Connecticut:
See Massachusetts.

Maine:
Chris Grigsby
MOFGA Certification Services
294 Crosby Brook Rd.
P.O. Box 170
Unity, ME 04988
(207) 568-6030
email: certification@mofga.org
www.mofgacertification.org

Massachusetts:
Don Franczyk (Main Office)
Baystate Organic Certifiers
1220 Cedarwood Circle
N. Dighton, MA 02764
email:    dfranczyk@baystateorganic.org
Phone: (774) 872-5544
http://baystateorganic.org

New Hampshire:
Allen Wyman, Director
New Hampshire Department of Agriculture
Division of Regulatory Services
25 Capitol St. P.O. Box 2042
Concord, NH 03302-2042
(603) 271-7761
email: Allen.G.Wyman@agr.nh.gov
 
Rhode Island:
Matt Green
DEM Div. of Agriculture
235 Promenade St.
Providence, RI 02908
(401) 222-2781 x2774516
email: matt.green@dem.ri.gov
 
Vermont:
Nicole Dehne
Vermont Organic Farmers, LLC
P.O. Box 697
Richmond, VT 05477
(802) 434-4122
email: nicole@nofavt.org
www.nofavt.org/vof