Phosphorus balance in paddy soils and its environmental effect under different phosphorus application rates

【Objectives】 The objective is to provide the basis for reducing agricultural non-poimt source pollution by evaluating phosphorus (P) balance in paddy soils in red soil zone of south China and its environmental effect under different P application rates. 【Methods】 A continuous 3-year (2011-2013) field experiment design was used, and 4 different P application rates were selected, P2O5 0, 63-81, 126-162 and 252-324 kg/hm2. In this study, yields and P concentrations of grain and straw of both early cropping rice and late cropping rice were detected, and P surplus was calculated by the difference of P levels and aboveground P accumulation. Moreover, total P in field water above soil surface at 1, 2, 3, 5,7 and 9 days after the basal and earing fertilizing was also detected, then the relation between total P in field water above soil surface and soil Olsen-P concentration from 2011 to 2012 year was analyzed by the split-line model. 【Results】The P2O5 63-81 kg/hm2 phosphorus treatment significantly improves the rice yield as compared with the non P fertilization control, and not significant as compared with the treatment of double and 4 times P rates of the fertilizer. The fertilizer-P application increases the aboveground P accumulation, soil P surplus and soil Olsen-P concentration which are increased with the increment of the P fertilizer amounts. The total phosphorus (TP) in the field water is high during the first 1-3 days in the control, which is the dangerous duration for P running off. Compared with the control, the TP content in the surface water of the P2O5 63-81 kg/hm2 treatment is significantly higher within 2 days after the fertilization, and always high during the monitoring period in the P2O5 252-324 kg/hm2 treatment. The simulation with the split line model on the relationship between soil Olsen-P and field water TP above soil surface shows that the change point of soil Olsen-P which relates to the field water TP concentration above soil surface is 19.0 mg/kg, corresponding to a P application rate of about P2O5 63 kg/hm2, and equals to the recommended fertilizer rate based on the line relationship model between fertilizer-P application rate and P surplus. 【Conclusions】 As far as the rice yield, soil P surplus and its environmental effect are considered, P2O5 63 kg/hm2 is suitable for the double rice cropping system in red soils of South China.