Effects of nitrogen application and irrigation on soil nitrate accumulation, nitrogen balance and use efficiency in summer maize

The field experiment was carried out to investigate the effects of different nitrogen and irrigation levels on soil nitrate accumulation, nitrogen balance and use efficiency in summer maize using the split-plot design. There were three irrigation levels, 900 (W900), 1200 (W1200), and 1500 m3/ha (W1500) in main plots and four nitrogen levels, 0 (N0), 150 (N150), 210 (N210), and 270 kg/ha (N270) in sub-plots. The results show that, the highest soil NO-3-N content is observed at 0-20 cm soil layers at the harvest stage of summer maize. Soil NO-3-N contents fluctuate with the increase of depth in 0-200 cm soil profiles. There is significant correlation between NO-3-N accumulation amounts in the soil profile and the nitrogen application amounts, the NO-3-N accumulations of the nitrogen treatments are significantly (P＜0.05) higher than those of the non-nitrogen treatments. The crop nitrogen uptakes and nitrogen apparent losses are positively correlated with the nitrogen application rates. As the total nitrogen input increased by 1 kg, the crop nitrogen uptake and nitrogen apparent losses are increased by 0.301 and 0.546 kg, respectively. The nitrogen apparent losses in the soil profile are decreased with the increase of the nitrogen application. The nitrogen harvest index and grain N absorption of summer maize are increased with the increase of the nitrogen application. The highest nitrogen recovery efficiency and agronomic use efficiency are obtained in the treatment of W1500N150, about 46.15% and 12.98 kg/kg, respectively, and the highest physiological use efficiency is observed in the treatment of W1200N150, about 34.49 kg/kg. In our experiment, the optimal combination of nitrogen and irrigation isW1500N150 for the lower amount of soil NO-3-N residual and nitrogen apparent losses, and the highest nitrogen recovery efficiency and agronomic use efficiency.