Nitrogen Management and Interseeding Effects on Irrigated Corn and Sorghum and on Soil Strength1

Abstract

AbstractA 15‐yr experiment on Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) investigated N management effects on corn (Zea mays L.) and grain sorghum [Sorghum bicolor (L.) Moench] grown side by side, under identical furrow‐irrigated conditions. Included were comparisons of anhydrous ammonia (AA) and N solution (UAN) as N sources, planting time (UAN‐PL) vs. summer sidedressing (UAN‐SD) application of the N, and rates of 90,180, and 270 kg N ha−1. Additionally, interseeding of rye (Secale cereale L.) into high N plots and alfalfa (Medicago sativa L.) into check plots of corn was accomplished at the time of ridging for furrow irrigation. The objectives were to evaluate the long term effects of varied management of the two N carriers and the interseedings on grain yields and N utilization, and the relative effects of these treatments on soil strength. Grain sorghum was the more productive crop under conditions of low N availability while corn responded to higher N rates, becoming the more economic crop with yields approaching 10 Mg ha−1 when N was plentiful. Yield increases averaged 5% greater for UAN‐SD over UAN‐PL, and AA was slightly more effective than UAN‐SD for both crops. Interseeded alfalfa and rye green manures provided average corn yield increases of 880 and 585 kg ha−1, respectively, explainable in part by improved N economy. No significant differences in penetrometer or vane shear tests were found between soils from AA and UAN‐SD plots, although there was a tendency toward lower soil‐strength values with both N carriers, relative to check plots.