Soil nitrogen dynamics in winter cover crop‐corn systems

Abstract

Understanding seasonal soil mineral nitrogen (N) dynamics under various cover cropping systems will aid in making supplemental fertilizer N recommendations for corn (Zea mays L.) using soil nitrate testing. A split‐plot field study was conducted to track early season soil mineral N under corn grown after cover crops and to determine the usefulness of the pre‐sidedress soil nitrate test (PSNT) in cover crop‐corn systems. The cover crop treatments rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), rye+hairy vetch, and fallow were established as main plots to provide a range of soil N availability for a subsequent corn crop. The split plot treatment was sidedress fertilizer N rate, which consisted of six rates ranging from 0–250 kg N ha‐1 in 50 kg increments. Soil was sampled throughout the growing season and corn was sampled at Hanway's corn growth stage 5 in the 0 kg N ha‐1 check plots to assess periodic soil N availability. Soil N concentrations peaked between Hanway's corn growth stage 1 and 3 and were concentrated in the top 15 cm of the soil. Vetch and fallow treatments provided higher amounts of available N as indicated by soil and corn N concentrations and corn yields. Recommended PSNT sampling times resulted in critical soil [NO3‐N] values that are similar to those used for PSNT fertilization; however, sampling to a depth of 15 cm may be adequate when a considerable portion of plant available N is supplied by cover crops. Addition of NH4‐N to NO3‐N testing did not improve the predictive capability of the soil test for supplemental corn N needs. The time of sampling may be delayed as much as two weeks without a loss of prediction accuracy.