Chapter 7

Crop Rotation on Organic Farms

Benefits of Crop Rotation

Crop rotation has many agronomic, economic and environmental benefits compared to monoculture cropping. The benefits of crop rotation can be substantial and provide a foundation for a profitable organic farming system. Appropriate crop rotation increases organic matter in the soil, improves soil structure, reduces soil degradation, and can result in higher yields and greater farm profitability in the long-term. Increased levels of soil organic matter enhance water and nutrient retention, and decreases synthetic fertilizer requirements. Better soil structure in turn improves drainage, reduces risks of water-logging during floods, and boosts the supply of soil water during droughts. The effects of crop rotation can be experienced in several different aspects of production.

Soil Properties

Rotations that include crops such as legumes or perennial grasses can add considerable organic matter to the soil by decomposition of above and below ground plant material. These roots maintain or increase soil humus (long-lasting organic matter).

Nitrogen Contributions from Legumes

When used strategically in a rotation, legumes such as alfalfa or soybeans provide nitrogen to the subsequent crop. A legume is typically followed by a high nitrogen-demanding crop such as corn or wheat. The amount of nitrogen that a legume crop contributes to following crops depends on the amount of nitrogen fixed, the maturity of the legume when it was killed or incorporated into the soil, whether the entire plant or only the root system remains in the field, and the environmental conditions that govern the rate of decomposition.

Nutrient Recycling

Crop rotations that integrate deep-rooted crops with shallow-rooted crops can help cycle nutrients in the soil profile. The deep-rooted crops absorb nutrients from deep in the soil profile and move them to the plant’s top growth. As crop residues are returned to the surface soil, these newly “mined” nutrients are potentially available to future crops.

Disease Management

Crop rotation can be an effective disease management tool, particularly if the pathogen has a narrow host range and overwinters in crop residue or soil. Crop rotation can decrease the level of inoculum present by introducing a crop that is not a host to the pathogen.

Insect Management

Rotating crops may help manage some insect pests. Crop rotations are most effective against insects that are fairly non-mobile, that feed on a narrow range of crops, and that overwinter in the soil as eggs or larvae.

Weed Management

Crop rotation provides the foundation for long-term organic weed management. Planting a wide variety of crops with varied characteristics reduces the likelihood that specific weed species will become dominant, and even “trap” weeds into life-cycle dead ends that curtail reproduction.

Soil Moisture Utilization

Crop rotation can lead to greater overall efficiency in soil water utilization. For example, deep-rooted crops such as sunflower following small grains can take advantage of the extra reserve of deep moisture and also any nitrogen that was not available to a shallow-rooted crop.

Improvement in Crop Yields

Yields are higher when a crop different than the preceding crop is grown. For example, growers have reported an increase in crop yields by as much as 10 percent or greater for both corn and soybeans, when they are grown in a rotation, compared to either continuous corn or continuous soybeans.

Added Benefits

Crop rotations can balance the production of crop residues when crops that produce durable residue (such as corn) are rotated with crops that produce more fragile residue (such as soybean).

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