Characteristics of Phosphorus Runoff Losses from Typical Paddy Fields in Guangdong Province, China

Three experimental paddy fields located in the city of Zengcheng, Qingyuan and Gaozhou in Guangdong Province were selected to monitor the runoff losses of phosphorus from the year of 2008 to 2012. The results showed that runoff event in paddy field occurred mainly in the early rice season. The runoff concentration of total phosphorus(TP) under conventional fertilization treatment was in the range of 0.02~1.56 mg·L^-1. It was recorded that TP concentration in 11%~18% of the total runoff samples exceeded the grade Ⅴ of the national surface water environmental quality(0.4 mg·L^-1). Peak concentration of different phosphorus forms[TP, dissolved total P(DTP) and particulate P(PP)] were observed within 14 days after fertilization, which indicated the high environmental pollution risk of phosphorus during this period. Application of phosphorus fertilizer increased runoff load of DTP in paddy field and showed no effect on that of PP and TP. The annual runoff loads of 0.63~4.05, 0.33~2.91 kg·hm^-2 and 1.10~6.68 kg·hm^-2 for DTP, PP and TP, respectively, were recorded under conventional fertilizer model. Runoff load of phosphorus exhibited wide spatial and temporal variation during experimental period. Runoff coefficient of 0.06%~6.81% of phosphorus was recorded. It was observed that DTP dominated the phosphorus runoff load. Phosphorus runoff losses from paddy field was affected by a variety of natural and human factors, and fertilization, precipitation and runoff volume were identified as the main factors