| Application of nitrogen （N） fertilizer is one of the most important measures that increase grain yield and improve grain quality of winter wheat．However?it is common that excessive N fertilizer is applied on fertility field?which not only causes the decline of N use efficiency and economic effects?but also results in larger amount of nitrate-N accumulated in soil?and so it is concerned to bring potential risk environment．Nitrogen （N） was manipulated through fertilizer application?to determine the extent to which these treatments alleviated a competition?and that this would be related to levels of resource availability?particularly available N．However application of N fertilizer not only helped control weed but also increased mineralization of the residues． Therefore?the experiment was a randomized complete block design consisting of two different factors．Nitrogen and weed treatments were arranged in a split—plot design with three replicates．Within normal density treatments five levels of nitrogen?0,45,90,135 and 180kg N／2were applied．Within each of these treatment combinations?different weed treatments were imposed．This experiment was carried out in Eum-Orthic Anthrosol located in the sem-i humid farmland ecological system．Soil sample was collected from0～100cm layer． Sample of crops and weed were collected from the winter wheat in different growth stage．The research was concerned to effects of different fertilizer and weed treatment on N fertilizer loses and N balance in sem-i humid farmland ecosystem．This experiment showed that residual nitrogen accumulation in soil increased with addition of N fertilizer application?but the ammonium nitrogen accumulation was stable．The total N mineralization increased with addition of N fertilizer application．The average value of Nitrogen uptake by weed in treatment A,B,C and D was respectively 2．38,160,4．72 and 4．54 kg N／2．Meanwhile?nitrogen uptake by weed accounted for 1．97％、1．38％、3．98％ and3．76％ of N uptake by aerial parts plant．N uptake of weed in the overwinter was the lowest．The N uptake of weed in the reviving stage is higher?which was the time2．94of N uptake by weed in over-winter．Nitrogen utilization rate decreased and apparent N fertilizer loss increased along with the increase of N fertilizer application．Apparent N fertilizer loss was the linear correlation with N fertilizer application?and the correlation coefficient R2 was0．9802?considering weed．The average of N fertilizer loss maintained between59．9and96．1 kg N／2 at different weed treatments．The average of N fertilizer loss was in the range of 32．9 to 128．0 kg／2 at different fertilizer treatments．There was obvious effect of removing weeds on N utilization rate and apparent N fertilizer loss at different time?especial before over-winter．There was no significant effect of weed on N balance. |