Effect of weed and nitrogen application on grain yield of summer maize and nitrogen use in semi-moist field

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/hm2, respectively. Total N uptake in Area B increased over Area A by 1.5, 2.9, 4.8, 5.2 and 4.3 kg/hm2, respectively. Across the whole growing stage, the change trends of organic nitrogen and accumulative mineral nitrogen in Areas 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/hm2, which was 1518.3 kg/hm2, and weed dry matter was lowest without N application, which was 845.7 kg/hm2. The weed N uptake increased with N rate. Removing weed from field could increase maize grain yield, improve NUE and decrease nitrogen loess.