Legume cover crop management on nitrogen dynamics and yield in grain corn systems

The N contribution of a legume cover crop may reduce fertilizer N inputs to subsequent grain corn (Zea mays L.). However, the best cover crop management options to maximize N to subsequent crop, as well as alternatives to red clover are largely unknown. A field study was conducted at two locations on two contrasting soil types in 2012-2013 and 2013-2014 to assess N dynamics and grain corn yield in a cover crop-corn rotation. Treatments included 1) cover crop; red clover (Trifolium pretense L.), crimson clover (Trifolium incarnatum L.), alfalfa (Medicago sativa L.) and no cover crop (no-cc); 2) cover crop seeding rate (3.36, 6.73, and 13.5 kg ha−1); and 3) cover crop termination timing (fall and spring). Plots were in a split-split plot arrangement. The following spring, no-cc plots were split into three with 0, 112 or 224 kg N ha−1 calcium ammonium nitrate applied (no-cc0N, no-cc112N, no-cc224N, respectively) to the corn crop but no fertilizer N was applied to plots with planted cover crops. Plant available N (PAN) was analyzed by measuring the sum of soil mineral N (SMN) in 0-60 cm depth and plant aboveground N content. In October SMN was 10 kg N ha−1 lower with the legume cover crop treatments compared to no-cc, suggesting these cover crops may mitigate N losses over the winter. The following May in spring-terminated plots, PAN was 20 kg N ha−1 lower in no-cc compared to red clover and alfalfa. At corn harvest, spring terminated plots had 14 kg N ha−1 higher PAN as compared to fall terminated cover crops. At corn harvest, PAN and corn grain yield were significantly higher by 21 kg N ha−1 and 1.0 Mg ha−1, respectively, in the highest (13.5 kg ha−1) cover crop seeding rate compared to the lowest rate (3.35 kg ha−1). Red clover or alfalfa sown at 6.7 kg ha−1 with spring termination is recommended to maximize N availability to subsequent corn crop. These observed effects were related to aboveground cover crop growth of alfalfa ≥ red clover > > crimson clover but only alfalfa and red clover had a positive impact on corn yield in one of two years. Management practices that improve crimson clover establishment and growth, as well as, a cost analysis associated with legume cover cropping are needed.