Abstract: Field studies were conducted to investigate effects of rice straw incorporation and nitrogen application models on process of nitrogen uptake by rice paddy ecosystem and fertilizer-N use efficiency in the double rice cropping system.Results show that rice straw incorporation coupled with N application at a proper rate could increase nitrogen uptake by rice plants and nitrogen cycling in the rice field ecosystem.In the treatment high in N application rate,nitrogen uptake by rice increased,but the amount of N transferred to the ears was limited and the rest still remained in the vegetative organs.N recovery rate,regardless of treatment,ranged between 26.7% and 30.7%,and N agronomic efficiency,between 10.5 and 12.2 kg·kg^-1.Obviously,fertilizer-N use efficiency is low,and it decreased with rising nitrogen application rate.Straw incorporation improved slightly use efficiency of applied N,including N agronomic efficiency,N physiological efficiency,and partial productivity,except for N recovery rate.According to the nitrogen absorption and transformation,the nitrogenous fertilizer use efficiency,and the fact that 7 500 kg·hm^-2 rice straw is incorporated annually,it is recommended that 185 kg·hm^-2 of N be applied a year in the red earth-paddy system.

Key words: straw incorporation, rice paddy ecosystem, nitrogen, uptake, use efficiency