Impact of Cover Crops On Nitrate Leaching Following Fall Nitrogen Application.

Nitrate loss studies in Midwestern tile-drained fields have found that residual N from the corn year of a corn/soybean rotation resulted in elevated nitrate concentrations in tile water during the soybean year, when no nitrogen was applied. Conventionally, cover crops have been used to scavenge this residual nitrogen that exists between cash crops. Thus, the objective of this study was to establish the ability of cover crops to reduce nitrate leaching from fall applied nitrogen. Experimental site was located at the Illinois State University farm in Lexington, IL. All treatments received fall nitrogen at a rate of 202 kg ha-1 into standing cereal rye, tillage radish, crimson clover and control (no cover crop). Cover crops were sampled and analyzed for total nitrogen to calculate N-uptake. Soil samples were collected in the spring at 4 depths to 80cm analyzed for nitrate. Both radish (226kg N ha-1) and rye (188kg N ha-1) had significantly higher N-uptake than clover (73 kg N ha-1 ). At the 0-20cm combined depths radish nitrate concentrations were similar to those of the control and Radish nitrate concentrations were 62% greater than rye and clover due to greater time for mineralization of nitrogen to occur. Fall applying nitrogen into cover crops significantly (p=0.027) reduced nitrate concentrations at the 20-80cm combined depths. At 20-50cm nitrate concentration in the control was 75% greater than radish and clover and 104% greater than rye. With the exception of rye, nitrate concentration in the control at the 50-80cm depth was 68% greater than radish and rye. The results of this study demonstrated that fall applying nitrogen into standing cover crops can increase fertilizer efficiency by stabilizing applied nitrogen near the soil surface, which reduces nitrate leaching.