Effects of nitrogen application dates on yield and nitrogen use efficiency of summer maize in super-high yield conditions

The effects of nitrogen application dates on grain yield, nitrogen translocation and use efficiency were studied under the super-high yield conditions. Denghai661 (DH661) and Zhengdan958 (ZD958) were selected experimental materials. The results show that the grain yield was not increased significantly under the single nitrogen application at the jointing stage, while the yields of two cultivars are increased significantly with the increase of nitrogen application times. Nitrogen application at the grain filling stage could increase weight of kernels significantly. The grain yield of DH661 is 14188.9 kg/ha, when the nitrogen fertilizers are applied at the jointing, male tetrad and grain filling stages, and the ratio is 2:4:4. The grain yield of ZD958 is 14529.6 kg/ha, when the nitrogen fertilizers are applied as the base fertilizer, and at the jointing, male tetrad and grain filling stages and the ratio is 1:2:5:2. Nitrogen accumulation amounts in the plant and grain, nitrogen harvest index, nitrogen agronomic efficiency, nitrogen recovery efficiency and nitrogen partial factor productivity are increased significantly with nitrogen application times and nitrogen application at the grain filling stage, and the active nitrogen accumulation period is prolonged. The ratio of nitrogen accumulation amounts before and after anthesis for DH661 is 51:49 by supplying nitrogen at the jointing stage (20%), male tetrad stage (40%) and grain filling stage (40%), while the ration for ZD958 is 60:40 for by supplying nitrogen at the jointing stage (30%), male tetrad stage (50%) and grain filling stage (20%). Nitrogen application several times before the anthesis stage could increase nitrogen translocation amount and nitrogen translocation efficiency, and nitrogen application at the silking stage could increase the assimilated amount of nitrogen in grain after anthesis. Through supplying nitrogen at the jointing stage (20%), male tetrad stage (40%) and grain filling stage (40%), the assimilated amount of nitrogen after anthesis is 63.0% of nitrogen accumulation amount in grain for DH661. Through supplying nitrogen at the jointing stage (30%), male tetrad stage (50%) and grain filling stage (20%), the assimilated amount of nitrogen after anthesis is 50.5% in grain for ZD958. In conclusion, under this field experiment conditions, as far as grain yield and nitrogen use efficiency are concerned, the jointing stage (20%), male tetrad stage (40%) and grain filling stage (40%) for DH661 and base fertilizer(10%), jointing stage (20%), male tetrad stage (50%) and grain filling stage (20%) for ZD958 are the most optimal nitrogen application stages and ratios.