Nitrogen Accumulation Rates of Irrigated Maize

Abstract

AbstractImproved fertilizer nitrogen (N) use efficiency in irrigated maize (Zea mays L.) often results from delaying application of moderate N rates until the crop is rapidly growing. The objective of this experiment was to determine how N application time, N rate, and planting date influenced the pattern of N and fertilizer−derived N (FN) accumulation in irrigated maize grown on a deep, productive silty clay loam soil (Typic Argiudoll, fine, montmorillonitic, mesic). A factorial combination of early and late planting, N application at planting, or at the 4−, 8− or 16−leaf growth stage, and two N rates (90 and 180 kg N ha−1 as 15N−depleted ammonium sulfate) were applied to the same plots in 1979–1980. Above−ground plant samples were taken at the 8−leaf, l2−leaf, silking, soft dough, and physiological maturity stages of growth. Average net rates of N and FN accumulation were calculated using a temperature index as the divisor. Rates of N and FN accumulation per plant were greatest between the 12−leaf and silking growth stages in 1979, except when N application was made at the 16−leaf stage where maximum accumulation rates occurred during early grain fill. Effects of N application time on N accumulation rates were more pronounced in 1980 and followed patterns similar to those in 1979. Substantial amounts of residual FN from 1979 accumulated in above−ground tissue in 1980. Residual FN uptake was apparently greater, in comparison to newly applied FN, in the heavily−fertilized or late−planted crop. Time of maximum N accumulation was delayed as time of N application was delayed. Grain yield was reduced by early N deprivation only when active N uptake ceased during early grain fill. Excessive N application minimized the effect of application time on final grain FN content. Delayed planting reduced FN recovery at both levels of N fertilization. Relative recovery of FN in maize grain was maximized by applying the low N rate late in vegetative growth, irrespective of planting date.