Optimal nitrogen rate for rice production by traded-off analysis between rice yield and environmental cost: a case study in Tai Lake region

In Tai Lake region, rice yield and its benefit responded to nitrogen rate in a convex parabolic curve based on results simulated by ORYZA v3 model, yet the nitrogen loss and its environmental damage responded in a concave parabolic curve. Assuming the partial income equal to the partial loss, optimal nitrogen rate trade-offed the rice productivity and environmental damage (ONREB) were determined under different rice and nitrogen price regimes. ONREB varied within the ranges of 215.4-294.1 kg N ha(-1) and 238.1-313.8 kg N ha(-1) in alternate wetting and drying (AWD) and flooded (FI) paddies. With rice price as 0.385-0.400 US$ kg(Y)(-1) and price of nitrogen pollution as 0.308 US$ kg(N) (-1), ONREB was estimated as 289-291 and 310-312 kg N ha(-1) in AWD and FI paddies. When nitrogen price increased to 2.462 or 3.077 US$ kg(N)(-1), ONREB will reduce to 247-252 or 236-242 kg N ha(-1) in AWD paddies and 269-273 or 259-264 kg N ha(-1) in FI paddies. Pricing nitrogen at a relatively high level (by incorporating cost for its environmental damage) or guiding farmers to increase their expected income will be an efficient tool for local government to reduce the nitrogen inputs in rice production.