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Application of nitrogen (N) fertilizer is one of the most important measures that increases grain yield and improves grain quality in winter wheat (Triticum aestivum L.) production.Presently,there is a large number of investigations (experiments) in the field on different nitrogen fertilizer application regimes.However,there still exists a serious problem of low nitrogen use efficiency,especially in winter wheat high yield conditions:unsuitable nitrogen fertilizer,which often leads to lower yield and large accumulation of nitrate in the soil,bringing a potential risk to the environment.In order to explore the optimal regime of nitrogen fertilizer application suitable for environment and economy,a field experiment on the different rate and ratio of base and topdressing of nitrogen fertilizer at the different growth periods of winter wheat was conducted.The field experiment was undertaken from the fall of 2003 to the summer of 2004 in the village of Zhongcun in Longkou city,in the Shandong Province of China.The field experiment with three repeats for each treatment was designed in a split-plot.The major plot was applied with urea at a nitrogen fertilizer rate of three levels,namely,0 kg·hm-2 (CK),168 kg·hm-2 (A),and 240 kg·hm-2 (B).In the sub-plot,the ratios of base and topdressing nitrogen fertilizer at the different development periods of wheat were 1/2:1/2 (A1 and B1),1/3:2/3 (A2 and B2) and 0:1 (A3 and B3).Treatment B1 was under a regime used now in the local region.It was found that the amount of N accumulation in plants had no significant difference between treatments applied with nitrogen fertilizer.The grain yield and grain protein content were all elevated remarkably by applying nitrogen fertilizer compared with those of treatment CK.There was no significant difference in the grain yield and grain protein content between A2 and B2 and B3.However,when compared with those of B2 and B3,in A2 there was an increase in nitrogen use efficiency and residual soil NO3--N and N losses were reduced.Under the condition of the same rate of nitrogen fertilizer,increasing topdressing nitrogen rate clearly elevated the grain yield,grain protein content and nitrogen use efficiency.The results indicated that the residual soil NO3--N in A1 and B1 accumulated higher than that of CK in 80-160 cm soil layers at the jointing stage,but that of A2 had no significant difference compared with that of CK in 0-200 cm soil layers.At the maturity stage,more residual soil NO3--N was detected in B2,B3 and A3 than that in CK in 120-180 cm soil layers,which could not be absorbed by the roots of wheat,but led to be eluviated easily.The amount of soil NO3--N accumulation in treatment A2 had no significant difference compared with that of treatment CK in the 100-200 cm soil layer.In conclusion,A2,whose nitrogen fertilizer rate was 168 kg·hm-2 and the ratio of base and topdressing was 1/3:2/3,had a higher grain yield and grain protein content,and heightened N use efficiency and minimized the risk of NO3--N leaching.This should be one of the most appropriate nitrogen fertilizer application regimes in wheat production in local regions in China.