Cover crop nitrogen availability to conventional and no-till corn: soil mineral nitrogen, corn nitrogen status, and corn yield

Understanding seasonal soil nitrogen (N) availability patterns is necessary to assess corn (Zea mays L.) N needs following winter cover cropping. Therefore, a field study was initiated to track N availability for corn in conventional and no-till systems and to determine the accuracy of several methods for assessing and predicting N availability for corn grown in cover crop systems. The experimental design was a systematic split-split plot with fallow, hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), wheat (Triticum aestivum L.), rye+hairy vetch, and wheat+hairy vetch established as main plots and managed for conventional till and no-till corn (split plots) to provide a range of soil N availability. The split-split plot treatment was sidedressed with fertilizer N to give five N rates ranging from 0-300 kg N ha(-1) in 75 kg N ha(-1) increments. Soil and corn were sampled throughout the growing season in the 0 kg N ha(-1) check plots and corn grain yields were determined in all plots. Plant-available N was greater following cover crops that contained hairy vetch, but tillage had no consistent affect on N availability. Corn grain yields were higher following hairy vetch with or without supplemental fertilizer N and averaged 11.6 Mg ha(-1) and 9.9 Mg ha(-1) following cover crops with and without hairy vetch, respectively. All cover crop by tillage treatment combinations responded to fertilizer N rate both years, but the presence of hairy vetch seldom reduced predicted fertilizer N need. Instead, hairy vetch in monoculture or biculture seemed to add to corn yield potential by an average of about 1.7 Mg ha(-1) (averaged over fertilizer N rates). Cover crop N contributions to corn varied considerably, likely due to cover crop N content and C:N ratio, residue management, climate, soil type, and the method used to assess and assign an N credit. The pre-sidedress soil nitrate test (PSNT) accurately predicted fertilizer N responsive and N nonresponsive cover cropcorn systems, but inorganic soil N concentrations within the PSNT critical inorganic soil N concentration range were not detected in this study.