Planting date and nitrogen management interactions in irrigated maize

Abstract

It is becoming increasingly important to develop economically and environmentally sound nitrogen fertilizer management practices. The objective of this experiment was to determine the optimum N application time-crop planting time combination(s) at two N rates which would maximize N fertilizer use efficiency (NFUE) and maintain high grain yields of irrigated maize ( Zea mays L.) in the western Corn Belt of the USA. Maize was planted three times at biweekly intervals during 1979–1981 on a Typic Argiudoll in eastern Nebraska. The 15N-depleted (NH 4) 2SO 4 was applied at rates of 90 or 180 kg N/ha in a band midway between maize rows at planting, or at the 4-, 8-, or 16-leaf growth stage during 1979–1980. Control plots (no N fertilizer applied) were maintained in each planting date. No N was applied during 1981 to allow study of residual treatment effects. Grain dry-matter yield and total N and fertilizer N (FN) contents of grain were determined, and NFUE was calculated as the fraction of FN in grain to applied FN. Very high N supply by the soil resulted in small effects of FN on yield and NFUE during the first year of treatment. According to the response surface analysis, greatest NFUE (52%) in concert with high grain yield (11.2 Mg/ha, the predicted maximum) would have been achieved by applying the low N rate at the 13- to 14-leaf growth stage to maize planted during the week before the average date of 10 May. Due to lower soil N supply the 2nd year of treatment, most corn with 90 kg N/ha did not produce near-maximum grain yields. However, yields within 10% of maximum were obtained when 90 kg N/ha was applied to the early planting at the 14- to 16-leaf stage, and NFUE was 67–71% with this treatment. Maximum NFUE with the application of 180 kg N/ha was only 44%. Recovery of residual FN in this silty clay loam soil was an important factor in the improvement of NFUE with delayed N applications the second year of treatment. In 1981, recovery of residual FN generally increased with a previous delay in N application time and was not greatly influenced by planting time. Early planting in combination with a modest rate of N applied very late during vegetative growth provided maximum recovery of FN in harvested grain, while maintaining high grain yields.