Abstract: A two-year field experiment was conducted to investigate effects of application of N fertilizer and incorporation of rice straw on nitrogen supplying capacity of the soil and rice yield under a double rice cropping system.Results indicate that soil NH⁺₄-N,mineralizable N and rice yield was significantly increased when the soil received N fertilizer,and the effect was more significant when rice straw was incorporated as well,showing a yield increase by 36.7%(in Treatment N₂,240 kg·hm^-2),and（40.4%-41.1%）(in Treatment N₁ and N₃,180 and 180 kg·hm^-2) respectively.In Treatment N₂ one kilo of N increased grain yield by（17.7-18.0） kg,which was quite similar in Treatment N₁ and N₃.The two treatments had the same total N application rate but differed in rate of each application.Rice straw incorporation in addition to N application,for two years in a row increased soil N supply,and the mineralizable N increased by（32.1%-50.0%）.With a proper N application rate,incorporation of rice straw could show more significant yield-increasing effect.It increased yield of the crop by 8.7% and 8.4% in Treatments N₁ and N₃,respectively,but only 5.1% in Treatment N₂,which was higher in N application rate.In the red soil paddy fields with a total of 7 500 kg·hm^-2 of rice straw incorporated into the field each year,the recommended N fertilizer application rate is 180 kg·hm^-2 per year,of which 30% is applied as basal dressing,30% as sidedressing at the tillering stage and 40% as sidedressing at the booting stage.