黄土高原旱地冬小麦/夏玉米轮作体系土壤的氮素平衡

Soil nitrogen balance in winter wheat and summer maize rotation system on dryland of Loess Plateau

在黄土高原南部旱地,通过田间小区试验研究了传统施肥方式下冬小麦/夏玉米轮作体系中土壤的氮素平衡。结果表明:土壤残留矿质态氮(Nmin)对作物产量和施用氮肥效果有重要影响,前季作物残留土壤Nmin可以促进后季作物生长,使氮肥增产效应不明显;冬小麦生长季节施氮240 kg/hm2可以增加产量和作物吸氮量,但其氮肥利用率只有39.7%,大部分以Nmin残留于0—200cm土壤中或以其他途径损失;由于冬小麦季节残留肥料氮的后效,使夏玉米生长季节的氮肥利用率很低,施氮120和240 kg/hm2的氮肥利用率分别只有22.4%和3.9%,而在0—200cm土层残留率则达到51.1%和87.2%;经过冬小麦、夏玉米一个轮作周期后,施氮量为240、360和480 kg/hm2时作物的氮肥利用率平均为52.2%4、2.2%和28.0%,而相应的土壤残留率平均为12.4%、25.3%和49.8%,表观损失率平均为35.4%、32.5%和22.2%。表明在土壤残留Nmin较高的条件下,夏玉米生长季节施氮量较低时盈余氮素以表观损失为主,施氮量高时大部分氮素残留于土壤剖面。

Field Experiments were carried out to study the soil nitrogen balance in winter wheat and summer maize rotation system under conventional fertilization condition on dryland in semiarid area, southern part of Loess Plateau. The selected N rates were 0 and 240 kg/ha for the winter wheat, and 0, 120 and 240 kg/ha for the summer maize. The obtained results showed that mineral N （Nmin） residual in soil had significant effects on crop yield and applied N fertilizer efficiency. Residual soil Nmin after winter crop had obvious benefits on the growth of following summer maize, resulting in a lower use efficiency of N fertilizer applied in latter growing season. Although applying 240 kg/ha N during winter wheat growing season could increase crop yield and N uptake, the N use efficiency was only 39.7 %, and the great mass of applied N fertilizer was left over in 0-200 cm soil layer or lost from the soil. Due to the after effect of residual N, the apparent N recovery of summer maize was quite low being 22.4% and 4.6% for N loading with N 120 and 240 kg/ha, however, the residual N in the 0-200cm soil layer accounted for 51.1% and 87.2% of applied N, respectively. Take the entire rotation duration into consideration, the mean N use efficiencies was 52.2%, 42.2% and 28.0% at N rates being 240, 360 and 480 kg/ha, respectively. As a result, the residual N was magnificently increased, correspondingly being 12.4 %, 25.3 % and 49.8 %. These implied that the application of N fertilizer during summer maize growing season mainly increased soil N residue at high N rates, and N loss could account for a great part at relatively low N rates,when the field had a great deal of residual Nmin in the soil profile.