Effects of tillage and straw returning on nitrogen leakage in double rice cropping field

Tillage affects the nitrogen leakage by changing soil physical and chemical properties. The effects of tillage on soil permeability and nitrogen leakage were studied for increasing utilization efficiency of nitrogen in paddy field. Long-term field experiments were established from 2005 in a double rice cropping region, Ningxiang county，Hunan province of China. Treatments included no-tillage with straw returning(NT), rotary-tillage with straw returning (RT), conventional tillage with straw returning (CT) and conventional tillage without straw returning (CT0). Constant-head method was used to analyze soil hydraulic conductivity in the soil layer 0-80 cm. Results showed that there was an increase in soil hydraulic conductivity in NT, which was 63.14% and higher than that in CT. Higher leakage of NH4+-N and NO3--N (p<0.05) were found in NT than in other treatments. Straw returning enhanced the leakage of NO3--N, especially in the period of early rice cultivation. The annual leakage of NH4+-N was almost two times than that of NO3--N among each treatment. Compared with other tillage treatments, NT could increase nitrogen leakage, and more attention should be focused on NH4+-N leakage in long-term flooding paddy fields.