Mineralization of Fall Applied N Following the Termination of Cover Crop Combinations.

Shalamar Armstrong¹ and Corey Lacey²

¹Illinois State University, Department of Agriculture, Assistant Professor of Soil Science, sdarmst@ilstu.edu; ²Illinois State University, Department of Agriculture, Master's Graduate Student Crops and Soil Science, cglacey@ilstu.edu 

Several studies, within the Midwestern Corn Belt, have demonstrated that fall application of nitrogen (N) increases the risk of nitrate leaching. However, recent surveys of N application timing have indicated that over half of the farmers in the region continue to fall apply N. Therefore, the objective of this study was to determine the efficacy of winter cover crops to sequester and release fall applied N in efforts to reduce the potential for N leaching. The experiment was conducted at the Illinois State University Teaching and Research Farm located in Lexington, IL, where fall N was applied (202 kg N ha^-1) to a control (no cover crop), standing Tillage Radish, Crimson Clover, and Cereal Rye. Plant samples were randomly collected from each plot one day before cover crop termination and were analyzed to determined plant N uptake. Following cover crop termination soil samples were collected in one week increments at a depth of 0-20 cm to evaluate soil N mineralization among treatments. Plant sampling data indicated that Tillage Radish (226 kg N ha^-1) and Cereal Rye (189.31 Kg N ha^-1) N uptake were significantly greater relative to Crimson Clover (73.65 kg N ha^-1). When comparing the impact of cover crops on the release of fall applied N, we found no differences among treatments for the first three weeks after termination. However, in the 5^th and 6^th weeks after termination the Tillage Radish treatment resulted in 208.11 and 192.80 kg N ha^-1 respectively, which were both significantly greater among treatment. Results from this study have demonstrated that cover crops, especially the Tillage Radish, have the potential to increase the efficiency of fall applied N via the sequestering and releasing of applied and residual soil N to the subsequent cash crop.