USE AND MANAGEMENT OF SOIL WATER AND NITROGEN RESOURCES Ⅱ-The simulation of use, loss and annual use efficiency of soil water and nitrogen resources

On the condition of winter wheat-summer corn cropping system in Beijing, the plant soil combined model is applied to simulate the annual relative yield of grain, the use, loss and annual use efficiency of soil water and nitrogen resources under various water and nitrogen management in this paper. The results of the simulation indicate that on the condition of normal rainfall year type of Beijing, annual irrigation amount 200～320mm and nitrogen application 320kg/hm2 are benefit to crop growth and soil water and nitrogen uptake. Thus the annual relative yield (RYA) can reach around 0.80 and the annual use efficiency of soil water resources(WUEA) can reach 0.910-4hm2/m23. But the rate of increase for RYA and WUEA is slow down when the annual N application is high than 400kg/hm2. Within this range of irrigation amount, as for NUEA, the highest limit of N application is 210kg/hm2. If over this limit, NUEA decreases because of the high N leaching and slow increment rate of N uptake. With the same N application amount, the equal partition of N fertilizer between the two crops or less for wheat and more for corn are benefit to raise the RYA, WUEA, NUEA, etc. The management of the water and nitrogen should be adjusted according to the forecast of the rainfall. In the wet year type, decrease of irrigation amount and control of the N application will greatly decrease the amount of N leaching.