[Temporal and Spatial Distribution of Phosphorus in Paddy Fields Under Cyclic Irrigation of Drainage Water]

Considering the potential of cyclic irrigation to increase rainfall use efficiency and reduce agricultural non-point pollution, the experiment of phosphorus transport in paddy fields under cyclic irrigation of drainage water was conducted to address the problem of phosphorus loss pollution and the mismatch between rainfall temporal distribution and crop requirement in the south of China. Lotus pond water and fishpond water were used to irrigate paddy fields for monitoring concentrations of total phosphorus (TP), dissolved phosphorus (DP), and dissolved reactive phosphorus (DRP) in surface water and leachate, and soil profile total phosphorus and Olsen-P concentrations. The results showed that the concentrations of TP, DP and DRP in surface water and leachate decreased along the field under cyclic irrigation of drainage water, especially the phosphorus concentrations of leachate dropped more obviously. As the phosphorus content of cyclic irrigation water sources varied within a certain range, phosphorus concentrations of surface water and leachate did not increased. The concentrations of TP, DP and DRP in surface water and leachate varied with cyclic irrigation time, and the least phosphorus concentrations were observed in August. Top soil Olsen-P concentration decreased along the field and increased with phosphorus content of cyclic irrigation water sources, and soil profile TP concentration was not influenced by cyclic irrigation. Phosphorus removal ratio of paddy field could be increased by extending field length or cyclic irrigation in August.