Improving the Efficiency of Fall Applied N with Cover Crops

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 objectives of this research were to (i) investigate the efficacy of winter cover crops to reduce nitrate leaching from fall applied nitrogen and (ii) investigate the impact of cover crops on N mineralization in the spring before planting main crops. 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 during the fall and spring months and analyzed for nitrate and ammonium. Despite variable weather conditions, both cover crop treatments demonstrated the potential to reduce nitrate leaching compared to a no cover crop control. The tillage radish treatment resulted in consistently greater soil inorganic N compared to other treatment immediately before planting. In contrast, cereal rye residue slowly decomposed over time and resulted in a slower rate of mineralization. Therefore, both cover crop species increased the efficiency of fall applied N by reducing nitrate leaching and increasing inorganic N at the soil surface