中文摘要：

为了探寻北京地区合理的施氮量，本文研究了冬小麦／夏玉米轮作体系下优化喷灌时不同施氮量对土壤氮素剖面分布、累积量和作物产量及氮肥利用效率的影响．研究结果表明在优化喷灌条件下单季施氮量为110kg·hm^-2时,土壤氮素含量没有出现增加现象；而单季施氮量大于等于220kg·hm^-2时，0-250cm剖面均显示出硝态氮累积量增加现象，且硝态氮的累积量随着施氮量的增加而增加．单季施氮量为220-550kg·hm^-2时3年氮素累积淋洗总量（淋洗到100-300cm土层内）在406-882kg·hm^-2之间；氮素淋洗均发生在夏玉米生长季节，而冬小麦季节在优化喷灌条件下未发生渗漏．由于研究区土壤中试验初有大量氮素累积，使得第一个试验季节，施氮与不施氮处理作物产量差异不显著；但是在后2个试验季节，与不施氮相比，单季施氮110kg·hm^-2能显著增加作物产量，单季施氮高于330kg·hm^-2时氮肥增产效果不明显．单季施氮量高于220kg·hm^-2时，作物氮肥利用效率急剧下降．综合经济效益和环境效益，建议该地区单季施氮肥为110kg·hm^-2较为合适．

英文摘要：

The effects of different nitrogen application rates on nitrate distribution, crop yield and nitrogen use efficiency in winter wheat-summer maize rotation cultivation system were evaluated in Beijing area. Data showed no increment in nitrate accumulation when nitrogen application rate was 110 kg·hm^-2, while great nitrate-N accumulation in 0-250 cm soil profile was found when the application rate was higher than 220 kg·hm^-2. The accumulated amount generally increased with rate increase. Total nitrate-N amount leached below 100 em soil depth ranged from 406 to 882 kg·hm^-2 after three wheat-corn seasons when application rate was from 220 to 550 kg N per season. In the winter season, nitrate-N did not leach into soil layer below 100 cm depth, where optimized water was applied to wheat using sprinkling irrigation system. However, in the summer maize season, there was great nitrate-N leaehout of 0-100 cm soil layer due to strong rainfall. N rates did not affect wheat and corn yields in the first year but significantly affected crops yields in the following two years, he yield could increase significantly when nitrogen application rate was 110 kg·hm^-2 per season compared to treatment with no nitrogen application, there was no significant increase in yield when nitrogen application rate was more than 330 kg·hm^-2 per season. Nitrogen use efficiency decreased sharply when nitrogen application rate was more than 220 kg·hm^-2 per season. Considering economic benefits （crop yield） and environmental benefits （nitrate-N leaching）, nitrogen application rate of 110 kg·hm^-2 per season was recommended for wheat and maize cultivation in Beijing.