Nitrogen and Phosphorus Losses from Corn-Soybean Rotations as Affected by Tillage Practices

THE effects of different tillage practices for continuous row cropping for corn-soybean rotations on the loss of NH4-N, NO3-N, and PO4-P in runoff and total N and total P in sediment were evaluated at two sites in Iowa by using simulated rainfall. Concentrations of NH4-N, NO3-N, and PO4-P in runoff water and, in general, concentrations of total N and total P in the sediment fraction increased following the order of tillage practices plow < chisel < no-till. However, because far more N and P were lost in eroded soil than in water and because erosion is in the reverse order, losses of nutrients were on the order, plow > chisel > no-till. To control nutrient losses, soil erosion must be controlled. Soybeans, except as they affect fertilization and soil erosion, had an effect on plant nutrient losses quite similar to that of corn.