Legume Cover Crops on Nitrogen Dynamics and Corn Yield in Southwestern Ontario.

The nitrogen contribution of a legume cover crop (cc) to subsequent field corn (Zea mays L.) may reduce nitrogen inputs. However, the best species, management and quantity of available nitrogen are largely unknown. Therefore a study was conducted at two locations in 2012-2013 and 2013-2014 in a split-split plot design to assess nitrogen dynamics and yield in an autumn cc-corn rotation. Treatments included cc species; red clover (Trifolium pretense L.), crimson clover (Trifolium incarnatum L.), alfalfa (Medicago sativa L.) and no cover crop (no-cc), cc seeding rates (3.36, 6.73, and 13.45 kg ha^-1), and termination timing (autumn and spring via tillage). Plant available nitrogen (PAN) was analyzed by measuring the sum of soil mineral nitrogen (SMN) from 0-60 cm and plant above-ground nitrogen content. Due to lack of interactions, random effects of rep, year and location were used in a mixed-model ANOVA. The cc seeding rate had no effect on SMN or PAN. SMN was 10 kg N ha^-1 lower for the cc treatments compared to no-cc in October. In May, cc species had no effect on SMN, however SMN was 15 kg N ha^-1 lower in the spring terminated plots compared to autumn due to the growing cc at the time of sampling. In October, no-cc had the lowest PAN (36.3 kg N ha^-1) and red clover was the highest (85.0 kg N ha^-1). In May, no-cc had the highest PAN compared to all cc autumn-terminated treatments, however in spring-terminated plots PAN was lower in no-cc compared to red clover and alfalfa. Legume cc appear to reduce SMN in the fall, while red clover and alfalfa increase overall PAN in the following spring. Despite differences in N dynamics, no differences were observed in subsequent 2013 corn yield except autumn-terminated plots had 1.09 Mg ha^-1 lower yields than spring-terminated plots.