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.  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.

Pest Considerations - 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 preventative 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.

Nutrient Management Considerations - 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.

Soil Health Considerations - 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 written weekly crop plan for the current season is a great method for planning your rotations, communicating with your crew about logistics, and to better plan cover crop systems and seed needs. Developing a written multi-year rotation plan that include your full rotations plan (3, 4, or even 5 year rotations) helps to visualize your full system including how fall crops or cover crops in one season will effect the following spring planting. For example, planting winter rye in one fall will make it difficult to plant early, small-seeded crops the next spring. 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 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. Remember that no crop rotation will ever be perfect. These plans are often disrupted by wet soils, crop emergence failures, equipment breakdowns, etc. That said, having a plan will significantly improve your ability to achieve goals related to crop rotation and cover cropping. 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