Study on Effect of Nitrogen Fertilizer and Nitrogen Balance in Winter Wheat and Summer Maize Rotation System

The effect of different rainfall years and different water and nitrogen management ways on winter wheat and summer maize was studied in northern part of North China Plain. The results showed that the highest yield was achieved when N fertilizer rate was 120 kg·ha -1 every season among the fertilizer rate of 0,120,240,360 kg·ha -1 . The yield decreased significantly when no nitrogen fertilizer was applied in two crops, but yield didn't increase even more N fertilizer was applied. 225 kg·ha -1 nitrogen application rate in three crops according to optimum nitrogen fertilization with strategy of soil testing had a similar yield with 900 kg·ha -1 according to conventional farming practice, which illustrated that yield would not decrease if using low amount of nitrogen fertilizer with strategy of soil testing. The main reason of yield change in years with same crop was different water supplying in years. All of nitrogen fertilizer, Nmin before sowing and mineralization played an important role in nitrogen input and total input significantly increased with nitrogen fertilizer increasing. Crop nitrogen uptake had not much change with nitrogen input increasing, Thus leading high nitrogen surplus with high nitrogen application rate. At high nitrogen application rate(≥240 kg·ha -1 ), the main form of surplus nitrogen was residual Nmin accumulated in soil profile and apparent nitrogen loss significantly increased with nitrogen fertilizer increasing.