THE FATE AND INFLUENCE OF BANDED FERTILIZER NITROGEN IN IRRIGATED MAIZE

Maize (Zea mays L.) was planted at three biweekly intervals in spring, 1978-81, on a productive, silty clay loam Typic Argiudoll in eastern Nebraska. (\u2715)N-depleted (NH(,4))(,2)SO(,4) was banded at 90 and 180 kg N ha(\u27-1) midway between maize rows at planting, or at the 4-, 8-, or 16-leaf growth stage in 1978-80. No N was applied in 1981 to allow study of residual treatment effects. Dry matter production, total N content, and fertilizer-derived N (FN) content of above-ground plants were determined at five growth stages in 1979-80 and at harvest every year. Surface soil samples were taken during maize growth and deep samples were procured after harvest, 1979-80. Soils were analyzed for mineral N and FN. High N supply moderated N management effects on maize growth, yield and N fertilizer use efficiency. Accumulated dry matter was usually greater for late- than early-planted maize during vegetative growth, but average relative growth rate was faster for the early planting after silking. Delayed planting reduced FN recovery at both N rates. Application of 180 kg N ha(\u27-1) at the 4-leaf stage decreased crop growth and final yield in 1980. Application of N at the 16-leaf stage increased rates of grain growth and N accumulation, resulting in greatest grain yield and FN recovery, especially with early planting. Grain yield was reduced by early N deprivation only when active N uptake ceased during early grain fill. Substantial amounts of residual FN accumulated in above-ground tissue the second year of treatment, especially with the higher N rate. Measurable amounts of NH(,4)(\u27+)-N derived from fertilizer were detected in soil 6 weeks after application. The amount of NH(,4)(\u27+)-N available to the crop during growth, in relation to the size of the developing root system and the availability of other N to the crop, may have been an important determinant of crop response. Early planting and application of a modest N rate very late in vegetative growth produced high grain yields and maximum recovery of FN in grain. Little mineral FN accumulated in the soil with this treatment, thereby reducing potential environmental problems