Impact of Rice Straw Incorporation and N Rates on Soil Nitrogen Supply and Rice Yield

A field study was conducted to investigate the effects of three year-rice straw incorporation and N rates on rice yield,nitrogen absorption by the crops at the different growths stages and nitrogen supplying capacity of soils in the double rice cropping systems.The results showed that the impacts of rice straw incorporation on soil NH4+-N and nitrogen absorption by the crops were different in different seasons.At the early rice season,rice straw incorporation in the last autumn increased soil NH4+-N and nitrogen absorption by the crops,while the effect was negative in the latter rice season with the fresh rice straw incorporated immediately after early rice maturing.After three years of straw incorporation treatment,the soil mineralisable N was increased by 35.4 %-53.9 %,and the dry matter weight of aboveground at all growth stages and grain yield were higher than those in the treatment of rice straw removing,and the rate of increase in grain yield was 4.0 %-4.7 %.The soil NH4+-N,mineralisable N,rice yield and the nitrogen absorption by the crops were significantly increased when received N,and the rate of increase in grain yield was 35.2 % and 45.3 %,but the N recovery rate was 27 % and 25 %,and the agronomic efficiency was 12.7 and 11.4 kg grain /kg N respectively under the treatments of the recommended N and farmer's N.