Cover Crop Impact On Nitrate Leaching Following Fall Nitrogen Application.

Nitrate loss studies in Midwestern tile-drained fields have found that fall applied nitrogen (N) resulted in elevated nitrate concentrations in tile water during both the corn and soybean year of a 2 year rotation. The effectiveness of cover crops to reduce nitrate leaching when N is spring applied has been well demonstrated, however there is a dearth of knowledge on the ability of cover crops to reduce nitrate leaching in a system where N is fall applied Thus, the objective of this study was to investigate the efficacy of winter cover crops to reduce nitrate leaching from fall applied nitrogen. The experimental site was located at the Illinois State University Research and Teaching farm in Lexington, IL.   All treatments received fall nitrogen at a rate of 200 kg ha^-1 into standing cereal rye, tillage radish 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 and analyzed for nitrate.  When averaged over the two years, all cover crop treatments reduced 0-80cm soil nitrate when compared to the control.    In spring 2012 rye and  radish reduced soil nitrate concentrations by 121.6 and 77.2 kg N ha^-1 respectively.  In spring 2013 rye  reduced soil nitrate concentrations by 87.4 kg N ha^-1 respectively.  Radish increased 0-80cm nitrate by 35.2 kg N ha ^-1.  However, this increase was only significant at 0-5 and 5-20cm depth; at lower depth radish was not significantly different from the control.  Rye, radish and clover all decreased nitrate leaching by reducing soil nitrate and have the potential to improve the efficiency of fall applied N.