Effects of fertilizer types on nitrogen and phosphorous loss from rice-wheat rotation system in the Taihu Lake region of China

Agricultural non-point source pollution is deteriorating water quality in many regions. Little information is available on the nitrogen (N) and phosphorus (P) loss via leaching and runoff for different fertilizer types in rice-wheat agricultural systems. A field experiment was conducted to quantify and characterize the temporal dynamics of N and P loss for different fertilizer types. A rice-wheat rotation with no fertilizer (Control, CL), chemical fertilizer (CF) and organic fertilizer (OF) was conducted from 2013 to 2015 in Taihu Lake. Fertilization and precipitation resulted in varied N and P loss within and between seasons. Compared to percolation water, runoff was the dominant mechanism for N and P loss. For N loss, runoff accounted for 81-90%, 91-98% and 70-94% for CL, CF and OF, respectively. Furthermore, NH4+-N was the major form for N loss in the rice season while NO3- + NO2--N (NOx) was the major form for N loss in wheat season. Particulate P was the major form for P loss, and accounted for 65-85%, 69-85%, and 51-60% for CL, CF and OF, respectively. Further, greater downward movement of P occurred for OF but greater N for CF, resulting in reversed N and P distribution with soil depth. Compared to CF, OF reduced N loss of 19-54% but increased P loss of 45-237%. Therefore, restricted use and better management of OF such as rotating OF applications with green manure and limiting the rates of OF are strongly suggested to enhance its environmental benefits in rice-wheat system. OF brings higher income with 226439 yuan ha(-1) compared to 48885 yuan ha(-1) for CF, but lower environmental cost with 418 yuan ha(-1) compared to 538 yuan ha(-1). Those make it feasible to control non-point pollution sources adjacent to rivers and lakes.