Can a Winter Rye Cover Crop or a Kura Clover Living Mulch Mitigate Nitrate Leaching in Corn Production on Irrigated Coarse Textured Soils?.

While productive, coarse-textured soils are vulnerable to nitrate (NO₃^- -N) leaching and ground water contamination. Previous studies found that leaching events occur most in early spring and late fall, when precipitation is high and crops have limited water and nutrient uptake. The objectives of this study are to measure the capacity of a rye (Secale cereal L.) cover crop to mitigate annual NO₃^- -N leaching and assess what effect this practice has on the economic optimum N rate (EONR) and yield of continuous corn (CC) and corn in a corn-soybean (CSb) rotation. Additionally, a kura clover (Trifolium ambiguum) living mulch was established to eventually plant corn and soybean crops into. During the establishment phase we monitored NO₃^- -N leaching. Urea, treated with a urease inhibitor, was applied at 0, 100, 200, 250, and 300 kg N ha^-1 with four split-timing applications at corn stages V2, V6, V8, and V12. 100 kg N ha^-1 were split applied to the kura plots. Soil water NO₃^- -N concentrations in rye, kura, and no cover plots were measured weekly using permanently-installed porous-cup suction lysimeters. The EONR and yield at the EONR for corn treatments were as follows: CC-rye cover (267 kg N ha^-1 and 16.2 Mg ha^-1), CC no cover (251 kg N ha^-1 and 16.0 Mg ha^-1), CSb rye cover (171 kg N ha^-1 and 16.1 Mg ha^-1), and CSb no cover (229 kg N ha^-1 and 16.4 Mg ha^-1). There was no difference in soybean yield. Averaged across N rates, the rye cover crop reduced load from 92 to 45 kg NO₃^—N ha^-1 in the CSb rotation but in the CC rotation there were no differences. The average load was 46 kg NO₃^—N ha^-1. There were no differences in NO₃^—N load due to N rate for any of the crop rotations. Kura produced 71 kg NO₃^—N ha^-1 during the establishment phase.