减量施氮对冬小麦-夏玉米种植体系中氮利用与平衡的影响

研究了冬小麦-夏玉米种植体系中减量施N对作物N利用与平衡的影响，结果表明，与原有高量施N处理(N240和N360)相比，在冬小麦季减半施N未引起产量和吸N量的变化。但在原有低量施N处理(N120)下减半施N显著降低了小麦产量和吸N量；在夏玉米季，在上季减半施N的基础上停止施N后作物产量和吸N量均比原固定施N处理显著下降，N平衡计算结果表明，减量施N条件下0～1m土壤N残留和表观损失的数量均显著低于原有施N量处理，作物N利用率显著提高，但在1～2m层次中累积的硝态氮却不因减量施N而下降，说明这一土层的硝态氮可能难以被作物吸收利用，由此可见，在前茬高施N量下减少氮肥用量有利于提高作物的氮肥利用率、减少N残留与表观损失。

Effect of reduced N application on N utilization and balance in winter wheat- summer maize cropping system

A field trial on a calcareous soil was carried out at an experimental station of China Agricultural University with the objective of assessing the effect of reduced nitrogen application on N utilization and N balance in a winter wheat-summer maize cropping system. Before this study, the trial has been conducted for one rotation cycle of wheat and maize with four-fixed N rates of 0, 120, 240 and 360 N kg.hm-2 per crop. In this study, each plot was divided into two sub-plots for two N application rates: normal N application(original rate) and reduced N application(reduced rate). The results showed that the grain yields of wheat and maize reached the platform at N rate of 120 kg.hm-2(N120), and then almost kept the same level regardless of the further increase of N rate(N240 and N360). The N uptake by wheat and maize followed the similar tendency like their yield. The grain yield and N uptake of wheat were not significantly declined with the half reduction of original N rate except the treatment N120. However, the same items in maize significantly declined with the further reduction of N fertilizer to zero. The residual NO3-N(main source of mineral N) in reduced N sub-plots was significantly lower in 0-1 m soil layer, but not different in 1-2 m soil layer compared with those receiving original N rate, indicating that 1-2 m soil NO3-N could hardly be utilized by crops. N balance calculation further showed that the N recovery by crops could be largely raised by the reduction of N fertilizer, while the apparent N loss rate decreased in wheat-maize rotation, respectively. Thus, the reduction of fertilizer N under high N rate can significantly increase N use efficiency and reduce NO3-N accumulation and apparent N loss.