Effects of rice cultivation patterns on nitrogen and phosphorus leaching and runoff losses

The loss of nitrogen and phosphorus due to excessive fertilizer application has become a major form in agricultural non-point pollution. In order to explore the impact of different planting patterns(conventional cultivation, green rice-frog ecosystem,organic rice-frog ecosystem) on nitrogen and phosphorus loss, a field experiment was conducted and the characteristics of nitrogen and phosphorus in surface water, runoff, leakage as well as rice yield differences analyzed in three paddy ecosystems. The results showed that among the paddy ecosystems, the order of average concentration of total nitrogen(TN) in surface water was:conventional cultivation(18.87 mg·L-1) green rice-frog ecosystem(8.98 mg·L-1) organic rice-frog ecosystem(8.20 mg·L-1).Compared with conventional cultivation, green rice-frog ecosystem and organic rice-frog ecosystem decreased TN loss during rice growth season by 15.27% and 25.76%, respectively. The TN runoff loss was in the following order: green rice-frog ecosystem conventional cultivation organic rice-frog ecosystem. NH4+-N was the main form of TN runoff. The order of TN leaching loss of was conventional cultivation green rice-frog ecosystem organic rice-frog ecosystem, with NO3--N as the main form of TN leaching. Also the ratio of total TN loss to nitrogen fertilizer use in the three treatments was in the range of 1.25% 2.38%, all less than 3%. Average total phosphorus(TP) concentration of surface water was in the following order: organic rice-frog ecosystem(0.82mg·L-1) green rice-frog ecosystem(0.64 mg·L-1) conventional cultivation(0.37 mg·L-1). Total loss of TP was in the order of:organic rice-frog ecosystem green rice-frog ecosystem conventional cultivation. Then the order of proportion of total loss ofphosphorous fertilizer was: green rice-frog ecosystem conventionally cultivation treatment organic rice-frog ecosystem, most of which was dissolved phosphorus. The order of rice yield under the three treatments was: conventional cultivation organic rice-frog ecosystem green rice-frog ecosystem. Compared with conventional cultivation, yield under green rice-frog ecosystem and organic rice-frog ecosystem decreased respectively by 19.33% and 8.15%. Research results showed that organic rice-frog ecosystem and green rice-frog ecosystem effectively controlled nitrogen and phosphorus loss in paddy fields although production decreased.Production quality and economic benefits of organic rice-frog ecosystem were better than those of green rice-frog ecosystem and conventional cultivation treatment. The requirements for organic rice-frog ecosystem were higher than those for green rice-frog ecosystem and conventional cultivation treatment.