Extended Crop rotation
An extended rotation is a farming practice that includes a primary row crop of corn, and at least two years of a different crop that typically is a forage legume, such as alfalfa. In practice, the specific rotation and crop combinations are extensive and may not be consistent on a given field. For Iowa, an extended rotation can be defined as a rotation of corn, soybean, and two to three years of alfalfa or legume-grass mixtures managed for hay harvest.
Extended rotations reduce the application and the loss of both nitrate-N and P. Due to growing nitrogen fixing legumes three years in a row, very little, if any nitrogen needs to be applied in the subsequent corn year. Research indicates an average 42% reduction in nitrate-N concentration in tile drainage water, with corn yields approximately 10% higher. The P loss reduction with alfalfa or a legume-grass mixture in the rotation is associated with reduced soil erosion because of greater soil cover, plus higher P removal with hay than with corn grain or soybean seed.