Snow removal and cover crops influence soil nitrogen transfer to the subsequent corn crop

Background and aims Cover crops can increase nitrogen (N) retention in agroecosystems by taking up soil soluble N when the grain crop is absent. We examined how the combination of cover crops and variability in winter conditions can affect soil N retention and N transfer to the subsequent crop. Methods We used 15 N tracer to quantify how the presence of cover crops (both winter-hardy and winter-killed) modifies the recovery by a corn crop of soil soluble N added the previous fall, and we used snow removal to assess how increased freezing would alter 15 N recovery. We predicted snow removal would decrease 15 N recovery in corn, and this decrease would be highest for plots with winter-hardy cover crops, given they remain vulnerable to increased frost over winter. Results Cover crops approximately doubled corn grain 15 N recovery (up to 8% of the added 15 N) relative to the treatment that lacked cover crops (4% of the added 15 N). Snow removal reduced 15 N recovery in corn grain, but this effect did not differ among cover crop treatments. 15 N recovery in soil at the time of corn harvest was increased by cover crops, with retention as high as 40% of the added 15 N tracer, compared to only 20% for soil in the control plots. Soil 15 N recovery was not significantly reduced by snow removal. Conclusion Although increased soil freezing reduced grain N recovery, cover crops increased soil N retention, which indicates decreased N losses to the surrounding environment, and the potential for increased contributions to grain N in future years.