TILLAGE AND NITROGEN MANAGEMENT EFFECTS ON CROP YIELD AND RESIDUAL SOIL NITRATE

Abstract

Tillage and N management can have great impact on crop yield and off-site transport of nitrate-nitrogen(NO 3 -N). This six-year field study on tile-drained Clyde-Kenyon-Floyd soils in northeast Iowa was conducted to quantifycorn (Zea mays L.) and soybean (Glycine max (L.) Merr.) yield and residual soil NO 3 -N. Eight treatments (chisel plow vsno-tillage by preplant versus late-spring N-management for both corn and soybean phases of a rotation) were evaluatedusing 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 andchisel treatments, respectively. No additional N was applied to soybean. Average corn yield on chisel plots wassignificantly (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 Mgha 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 NO 3 -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 NO 3 -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 soilNO 3 -N were greatest in corn plots previously fertilized with a single preplant application (+13 to 18 kg N ha 1 ) and mostvariable 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 ofN-cycling processes taking place in the soil profile over winter months. The results of the study demonstrate that chiselplow increased corn yield with late-spring N-management and with preplant N when compared to no-till system.