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 created for a variety of crop 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 breaks up the life cycles of some pests and diseases, as long as the next crop is an unsuitable host for them. Similarly, because weed management strategies can vary by crop, implementing several different strategies over a crop rotation can also reduce weed pressure in a field.

Many crop pests have specific plant family preferences or even requirements. A well-known example is the Colorado potato beetle’s preference for plants in the Solanum genus, especially potato and eggplant. For pests that are generalists, the strategy of crop rotation has minimal benefits. An example of this is the European corn borer, which can feed on corn as well as peppers, beans, potatoes, and many more crops, including ornamentals. Plant diseases follow a similar pattern: Alternaria solani, known as early blight specifically infects tomatoes, potatoes, and eggplant; 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 results in repeated cultural practices, such as tillage and fertilization, and crop nutrient uptake. Rotating a particularly demanding crop with one that is less demanding can conserve soil fertility and organic matter. A common example is planting leguminous crops like beans and peas after crops with heavy nitrogen demands like 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 greens, 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 between season to avoid creating 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 with either a cover crop, or a soil-building cash crop with high fertility residues, like a legume. 

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 better planning cover crop systems and seed needs. Creating a multi-year crop rotation plan can further help you to think through the intricacies of your full system, like how fall crops or cover crops in one season will affect the following spring planting. For example, planting winter rye in the fall will make it difficult to plant early, small-seeded crops the next spring. (Crop Rotation on Organic Farms: A Planning Manual is an excellent SARE resource for this purpose) Start by making maps and designating names to your fields using the USDA NRCS's Web Soil Survey.

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 should 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 plant and soil health goals. 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