Winter-Hardy Legumes Provide Significant Amounts of N to the Corn in a Soy-Wheat-Corn System in Southern Ontario, Canada.

The fallow period after winter wheat harvest in the humid temperate southern Ontario, Canada, bears a high risk for N leaching out of the crop root zone into the water systems, eventually into the Great Lakes in the region. Cover crops have the potential to reduce N losses and increase cropping system resiliency by providing nutrients to crops and adding organic residues to the soils. This study reports a 3-yr cover crop study including Crimson clover (CC), hairy vetch (HV), red clover (RC), and control. The objectives are to reports: (1) what is the reduction of residual mineral N in soil profile in cover crop fields before winter; (2) how much N can be fixed by cover crops; (3) what is the contribution of cover crops to the yields of subsequent corn. The contents of residual soil mineral N (nitrate) was around 75-80 kg N ha^-1 in 0-90 cm after winter wheat harvest for all treatments (including CK). After about 3 month cover crop growth (August – mid-November), the contents of residual soil nitrate N diverged (0-90 cm), with about a 10 kg N ha^-1 decrease in the cover crop treatments versus a significant increase (65 kg N ha^-1) in no cover crop control. Before freeze-up, the amounts of total N in above ground biomass were 126, 123, and 75 kg ha^-1, respectively, in CC, HV and RC treatments and 9.1, 16.9, and 24.8 kg ha^-1 in roots for corresponding treatments. The N contents in plant aboveground biomass changed to 103, 284 and 179 kg ha^-1 in CC, HV, and RC plots before corn planting in the following spring. Over winter HV and RC gained substantial amount of N while CC lost N. In 2016 which the cover crop treatments has been managed without chemical fertilizer use for three year, the corn grain yields were 13542 kg ha^-1 for the fertilized conventional control (CK) and only 5412 kg ha^-1 for the organic control (CKO). In comparison, the corn grain yields were 12852 kg ha^-1 for the CC, 13715 kg ha^-1for the HV and 13307 kg ha^-1 for the RC treatments, respectively.