The Studies On Effect Of Optimized N Fertilization Management In Winter Wheat-Summer Maize Rotation System At North China Plain

At North China Plain farmers were used to mass water and N fertilization input, but the crop yield was always not I)ositivety responsible to high input of nitrogen fertilizer and water in winter wheat-summer maize rotation system while wasting resource and possible negative effect on environment. The study intended to establish an optimized nitrogen management system, in which resources could be utilized with high efficiency, and constituted by optimized N fertilization at different stages (Winter wheat N demands which were according to N uptake in different stages, coupled with soil Nmin to optimized the time and the amount of N application in different stages) , optimized irrigation and optimized farm management. A field trial was carried out to study the effect of optimized nitrogen management system on crop yield, biomass, N uptake, soil Nmin and N balance by comparing those of conventional nitrogen managerial system and no N fertilization control. The main results were summarized as follows:1 For winter wheat the yields of optimized N fertilization treatment and conventional N fertilization treatment were not significantly different and achieved target yields. The amountof N fertili~er in optimized N fertilization treatment was 24kg/hm2 under suboptimizedirrigation condition and 78kg/hin2 under conventional irrigation and optimized irrigation condition. The results showed optimized N fertilization at different stages enhanced the profit of N application. 憀抙e dynamics of accumulated biomass between optimized N fertilization treatment and conventional N fertilization treatment was similar without difference. Without straw, at harvest total N uptake in conventional N fertilization treatment was significantly higher than that of optimized N fertilization treatment, but the superfluous N distributed in straw and N uptake of grain was not different between two treatments.2~ The summer maize yield between optimized N fertilization treatment and conventional N fertilization treatment was not significantly different. Because of the quality in sowing, there were too many young plants and the rate of coming into ears was rather low, which led to lower yield than target yield. Only combining optimized N fertilization technology and other technology for high yield could best use N fertilizer. The amount of soil N mineralization was large in high fertility soil, so the trend of summer tna?ze growth and N uptake was not different among optimized N fertilization treatment, conventional N fertilizatioii treatment and no N fertilization treatment.3.in winter wheat/summer maize rotation system, 0-90cm soil Nmin of optimized N fertilization treatment fluctuated between 8OkgIhm2 and l85kglhm2, which was slightly higher32001than that of control treatment, but there was much higher soil residual Nmin(290---5lOkg/hm2) in conventional N fertilization treatment.4.The input and output of nitrogen was almost balanced on the whole rotation season in optimized N fertilization system, the gain and the loss in 5OkgIhm2. In winter wheat N income and N expenses were approximately equal in conventional N fertilization treatment, while in summer maize N was seriously lost and the mean loss was I 33kgN/hm2. At summer maize harvest lots of N03-N moved below 90cm soil layer in conventional N fertilization treatment and accumulated in 90-200cm soil layer, but soil Nmin in 90-200cm of optimized N fertilization treatment had the least discrepancy with control treatment.