Crop Rotation

Crop rotation is one of the most effective tools for managing pests and maintaining soil health, but there aren't many specific recommendations for how to go about it. Each farm needs to develop a plan that fits its unique combination of crops, soils, equipment and environmental conditions. A common approach on vegetable farms is to rotate crops by families. Another approach is to alternate vegetable crops with field or forage crops, such as small grains or alfalfa. Some growers try to rotate fields so they are in cash crops one year and cover crops the next year. On farms with limited land available for rotation, sweet corn is a good rotation crop since it hosts very few insects or diseases that affect other vegetables. At a minimum: 1) the same crop should never follow itself in the same field (or bed, in the case of small farms); 2) a winter cover crop should be planted after annual vegetables every year if possible.

Too many growers rotate crops using a seat-of-the-pants technique, relying on memory and making decisions at the time of planting. To get the most benefit from crop rotation it’s better to plan ahead using written records of where crops were grown in the past. It also helps to have a written plan for how crops will be arranged in the future, even if it’s subject to change. Start by making a map of the farm and any available fields including those that are rented. Label the fields or sub-fields with names and acreage. Make photocopies of the map and at the end of each season fill one in for each field and date it, noting what was grown where, and any serious pest or soil problems. Prior to the growing season, fill in a new map with your best guess as to where crops will go in the field.

As you plan, remember that rotation helps prevent some pests but not others. For insects that over-winter near the crop they infest, such as Colorado potato beetle, European corn borer, or flea beetle, it helps to plant host crops as far away as possible the next year. Having a barrier such as a road or river between last year's crop and this year's crop can enhance the rotation effect. Rotation will not help prevent insect damage from pests that migrate into the area on storm fronts, such as potato leafhopper or corn earworm.

For diseases that are soil-borne or over-winter in crop residues, rotating out of susceptible crops is a key to preventing infection, as in the case of Phytophthora blight, early blight, and many other diseases. However, host crops must be rotated far enough away to avoid infection through blowing or washing soil. The movement of soil on equipment from field to field can also introduce diseases and weeds into a field. A few minutes spent cleaning equipment before moving from one field to another can help avoid spreading pest problems. For some diseases, such as club root of crucifers, susceptible weeds, in this case the mustard family, must be controlled if rotation is to be effective. As with insects, rotation cannot prevent airborne diseases that move in from other areas, such as downy mildew or late blight, nor can it prevent seed-borne diseases.

Rotating crops is good for soil health. It leads to changes in tillage intensity and crop nutrient removal but more important is the use of cover crops in the rotation. This practice is critical to sustaining production over the long-term. Even if growing cash crops in a field every year it is possible to build a rotation plan to maintain soil health by alternating the two main types of winter cover crops. Late-planted vegetables can be followed by winter-hardy cover crops that are used to build organic matter and add nitrogen to the soil; early-planted vegetables can be followed by winter-killed cover crops that add some organic matter and protect the soil over winter but make it easier to prepare an early-season seedbed. If possible, one should also include spring-planted and summer-planted cover crops when there is a space in the rotation.

Year-long fallowing with cover crops or forage crops gives fields a 'rest' from the intensive tillage and field traffic that vegetable production often requires. However, long-term cover crops are best suited to fields that are already low in weed pressure; the lack of tillage can promote extensive weed seed production or proliferation of perennial weeds. In fields with high weed pressure, shorter periods of cover crops are best to maintain soil health without losing ground to weed management. For a description of different cover crops suitable for sowing at different times of the season in our area see the Cover Crops section.

Ideas for rotations that include cover crops and vegetables in the New England:

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 plus 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

Plow oats plus hairy vetch

Direct seeded vegetables

Oats in the fall

Disk Oats

Field peas plus triticale in spring

Sudangrass or two crops buckwheat

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 peas

Early summer fallow

Sudangrass or Japanese millet

Disk Sudangrass or Japanese Millet

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 oats

Vegetable Crops

Oats in fall

Disk oats

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

For more information, see: Crop Rotation on Organic Farms

http://www.sare.org/Learning-Center/Books/Crop-Rotation-on-Organic-Farms