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, such a strategy does not work. 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 following with a susceptible crop.

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. 

It is a good exercise to develop a rotation scheme on paper, something that will help you to project your land use several years into the future. 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 of your fields. Use the USDA NRCS's Web Soil Survey, and see 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.

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