Synchronizing of the Mineralization of Cover Crops with Corn Growth Stages.

The ability of cover crops to scavenge nitrogen from the soil during winter months has been thoroughly investigated, however little is known about the return of nitrogen back soil from the cover residue or the rate of scavenged N release back to the soil solution via nitrification. Therefore, the objectives of this study were to: I) determine the impact of cover crop species on the release of N from the cover crop residue to the soil in the spring II) synchronize the release of inorganic nitrogen with critical corn growth stages, soil temperature, rainfall, and soil moisture. 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, daikon radish, cereal rye/daikon radish mixture, and control (no cover crop). Cover crops were sampled and analyzed for total nitrogen to determine N-uptake. After chemical termination of the cover crop, soil samples were collected biweekly and were analyzed for nitrate and ammonium to capture the release of inorganic N from the cover crop residue during the period of linear increases in soil temperature.  Over three years, cover crop treatments produced on average 33.8kg ha-1 more inorganic N than the control treatment at the time of corn planting.  After the linear increase in soil temperature in the spring (~42 days after cover crop termination), cover crop treatments averaged 88.0kg ha-1 more inorganic N compared to the control treatment.  This three year study has demonstrated that fall applying N into a living stand of cover crop results in greater inorganic N at planting and prior to corn growth stages of rapid uptake relative to the control where no cover crop was present.