Tillage and nitrogen management effects on crop yield and residual soil nitrate

Tillage and N management can have great impact on crop yield and off-site transport of nitrate-nitrogen (NO3-N). This six-year field study on tile-drained Clyde-Kenyon-Floyd soils in northeast Iowa was conducted to quantify corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) yield and residual soil NO3-N. Eight treatments (chisel plow vs no-tillage by preplant versus late-spring N-management for both corn and soybean phases of a rotation) were evaluated using a randomized complete block design. Preplant N was applied by injecting liquid urea-ammonium nitrate solution (UAN) at a rate of 110 kg N ha-1. Late-spring soil-test based N-rates averaged 179 and 156 kg N ha-1 for no-till and chisel treatments, respectively. No additional N was applied to soybean. Average corn yield on chisel plots was significantly (P = 0.05) higher than with no-tillage for both preplant (7.9 vs 6.9 Mg ha-1) and late-spring (8.6 vs 8.1 Mg ha-1) N-management. Average soybean yield where corn had received preplant N (3.6 Mg ha-1) was significantly (P = 0.05) greater than where late-spring N-management (3.4 Mg ha-1) was used. Residual tillage effects did not significantly (P = 0.05) affect soybean yield. The average residual soil NO3-N to a depth of 1.2 m following corn was significantly (P = 0.05) lower for preplant (21 kg N ha-1) than late spring (29 kg N ha-1) N-management under no-till system, presumably reflecting differences in N application rates. Residual soil NO3-N following soybean was significantly (P = 0.05) lower in no-till (28 kg N ha-1) than chisel (37 kg N ha-1) plots. Average over-winter changes in residual soil NO3-N were greatest in corn plots previously fertilized with a single preplant application (+13 to 18 kg N ha-1) and most variable following soybean in plots where corn was fertilized based on late-spring nitrate test (LSNT) values (-8.5 to +6.3 kg N ha-1). Therefore development of efficient N-management strategies may require complete understanding of N-cycling processes taking place in the soil profile over winter months. The results of the study demonstrate that chisel plow increased corn yield with late-spring N-management and with preplant N when compared to no-till system.