Fertilizer Nitrogen Utilization by Corn, Tomato, and Sugarbeet1

Abstract

AbstractDifferences in the abilities of crops to utilize fertilizer and soil N can contribute to the establishment of rotation systems to improve the efficiency of fertilizer use and reduce nitrate pollution groundwater. Field studies show considerable site variability in the utilization of fertilizer by individual crops. To compare fertilizer N use by corn (Zea mays L.), sugarbeet (Beta vulgaris L.), and tomato (Lycopersicon esculentum Mill.), several rates of fertilizer N were applied to replicated plots of each crop in the same field at Davis, Calif. A 2nd year study involved only corn and sugarbeet. The experiments were conducted at different sites, but both on the same soil, Yolo silt loam (a fine‐silty, mixed, nonacid, thermic, Typic Xerorthent). Nitrogen‐15 depleted ammonium sulfate was used as a labeled N source in the three‐crop experiment and ammonium nitrate of normal isotopic ratio was used for the two‐crop experiment. In both experiments, N was applied in bands on both sides of crop rows after seedling emergence in 56 kg increments from 0 to 280 kg N/ha. Fertilizer N required for maximum commercial yield in 1979 was: corn 194, tomato 131, and sugarbeet 92 kg N/ha; and in 1980: corn 280 and sugarbeet 70 kg N/ha. Average recoveries of labeled N from fertilizer in 1979 were: corn 57%, and tomato and sugarbeet 27%; and in 1980 without labeled N the apparent recoveries were: corn 52% and sugarbeet 37%. The ratios of fertilizer to soil N in the crops at fertilizer rates giving maximum commercial yields in 1979 were: corn 45/55, tomato 25/75, and sugarbeet 15/85; and in 1980 were estimated by the difference method to be: corn 54/46 and sugarbeet 10/90. Thus corn relied most heavily on fertilizer N, followed by tomato then sugarbeet. On average, over the 2 years, sugarbeet took up 95% more soil N than corn. These data indicate that fertilizer use efficiency may be improved by growing corn when residual N is lowest and tomato or sugarbeet when residual N is highest. With care to avoid residual N too high for depletion prior to harvest, sugarbeet can be used to scavenge soil N and thus conserve the use of fertilizer N.