Synchronization of Mineralized N from Cover Crop Residue with Corn Growth Stages.

The ability of cover crops to scavenge nitrogen from the soil during winter months has been thoroughly investigated. Following the termination of cover crops, little is known about the synchronization of cover crop residue N mineralization and corn growth stages. Therefore, the objectives of this study are to determine the impact of cover crop species on the release of fall N following termination and to relate cover crop residue N mineralization to the growth stages of the corn plant. The experimental site was conducted 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, tillage radish/cereal rye mixture, and control (no cover crop).  After termination soil samples were collected at the 0-20cm depth biweekly and were analyzed for nitrate and ammonium to estimate N mineralization and nitrification.  The tillage radish treatment, relative to cereal rye, contained greater soil nitrate immediately before corn planting and throughout the growing season. In the spring of 2013, tillage radish had a soil nitrate concentration almost two times greater than the control and cereal rye at the V6 corn growth stage.  At the V8-V11 corn growth stages in the spring of 2013 the tillage radish, tillage radish/cereal rye mixture, and cereal rye treatments resulted in 57, 25, and 4 kg ha^-1 more soil nitrate relative to the control respectively. All cover crop treatments resulted in greater soil inorganic N at critical corn growth stages throughout the growing season relative to the control.