Nitrogen Uptake by Rice Paddy Ecosystem Based on Rice Straw Incorporation

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.