中文摘要：

以土垫旱耕人为土为供试土壤，采用大田试验，研究了半湿润农田两种杂草处理方式下（成熟后期清除杂草-A区和苗期开始清除杂草-B区），不同施氮量对夏玉米产量及氮素利用效率的影响。结果表明，当施氮量为0、45、90、135、180kg／hm^2时，B区玉米子粒产量比A区分别增加了8．7％、12．1％、9．4％、5．0％和12．5％；吸氮量分别增加了1．5、2．9、4．8、5．2和4．3kg／hm^2。A区和B区全生育期0-100cm土层矿质氮（Nmin）累积量变化趋势基本一致，但B区比A区变幅较大。当施氮量为45、90、135和180kg／hm^2时，B区氮肥利用率、氮肥农学利用率、氮肥生理利用率均高于A区。研究还发现，在A区，当施氮量为180kg／hm^2时，杂草干生物量最大，为1518．3kg／hm^2，不施氮时，杂草的生物量最低，为845．7kg／hm^2；杂草的吸氮量随施氮量的增加而增加。可见，清除玉米农田杂草不仅可以提高作物产量和氮肥利用率，而且在减少氮素损失方面具有一定作用。

英文摘要：

A field experiment was carried out using loess soil to study the effect of different N rates on grain yield and nitrogen use efficiency as affected by two different weed treatments [ weed removed at harvesting stage （Area A） and at seedling stage （Area B）]. The result showed that grain yield in Area B increase by 8.7%, 12.1%, 9.4%, 5.0 % and 12.5% than grain yield in Area A for N rates of 0, 45, 90, 135 and 180 kg/ha, respectively. Total N uptake in Area B increased over Area A by 1.5, 2.9, 4.8, 5.2 and 4.3 kg/ha, respectively. Across the whole growing stage, the change trends of organic nitrogen and accumulative mineral nitrogen in Area A and B were similar, however, the range of Nmin change in Area B was higher than Area A. Nitrogen use efficiency （NUE）, N agronomic efficiency （NAE） and N physiological efficiency （NPE） in Area B were higher than those in Area A at different N rates. The result also showed that in Area A weed dry matter was largest when N rate was 180 kg/ha, which was 1518.3 kg/ha, and weed dry matter was lowest without N application, which was 845.7 kg/ha. The weed N uptake increased with N rate. Removing weed from field could increase maize grain yield, improve NUE and decrease nitrogen loess.