Effective use of cover crops in rotations involving corn, soybean, or winter wheat in S. Ontario

Soybean-winter_wheat-corn rotation is common for grain growers in humid southern Canada. There is a fallow period during rotation, from wheat harvest (late July) to the following corn planting (May in next year). This bears a high risk for nutrients leaching from the crop root zone into the water systems, eventually into the Great Lakes in the region. We aim to include one seasons of cover crop into the rotation and to determine the amount of nitrogen in cover crops, the reduction of residual mineral N in soil profiles before dominant leaching season, and nitrogen credit to the yield of following crop corn.
Winter-hardy legumes were planted after winter-wheat harvest, included Crimson clover, hairy vetch, and red clover. Two non-cover crop controls (with/without fertilization) were included. This study (2013-2016) was arranged in a randomized complete block design (4 reps) on a sandy loam.
Before freeze-up, the averaged amounts of nitrogen in aboveground biomass were 126, 123, and 76 kg/ha, respectively, in Crimson clover, hairy vetch and red clover and changed into 104, 283 and 180 kg/ha for corresponding treatments in following spring before corn planting. The contents of soil mineral N was around 75-80 kg N/ha in 0-90 cm after winter wheat harvest for all treatments. After 3 plus months, the contents of residual soil mineral N diverged, with a 10 plus kg N/ha decrease in cover crop treatments versus a significant increase (65 kg N/ha) in non-cover crop controls. The corn yields were 14525 kg/ha for the fertilized control and only 6181 kg/ha for the unfertilized control. In comparison, the corn yields were 11762, 12756 and 12280 kg/ha for Crimson clover, hairy vetch and red clover, respectively. The use of winter-hardy legumes after winter wheat has significant contributions to the agro-ecosystems and to the corn production in the region.