Abstract: 9 years field experiment on N and P balances in farmland ecosystem shows that the application of N and P fertilizers with stalk returned to soil can increase the contents of soil organic matter and total nitrogen, and its available and non-available P pools are supplemented. In last years, the utilization efficiency of P fertilizer is 22.1-65.1%, and that ofN fertilizer is 49-75%. The application of storable P only has an efficiency of 6.5-7.3% in the first year, and its total efficiency in-first three years is 24-28.5%. The average utilization efficiency of applied P In nine years is 27.9-48.8%, and that of supplemented P is 19.5-42.9%. The application of 65.5kg P.ha^-1. yr^-1 can both satisfy the Prequirement of crops and supply the available P pool in soil.

Key words: Farmland ecosystem, Nutrient balance, Residual effect of P fertilizer, Nitrogen fertilizer, integrated crop-livestock system, livestock, crop, carbon fixation., carbon emission