EFFECT OF APPLICATION RATE OF NITROGEN ON NITRATE DISTRIBUTION AND ACCUMULATION IN SOIL PROFILE AND THEIR EFFECTS ON CROP YIELD IN WINTER WHEAT-SUMMER MAIZE ROTATION SYSTEM

The effects of different nitrogen application rates on nitrate distribution,crop yield and nitrogen use efficiency in winter wheat-summer maize rotation cultivation system were evaluated in Beijing area.Data showed no increment in nitrate accumulation when nitrogen application rate was 110 kg·hm-2,while great nitrate-N accumulation in 0~250 cm soil profile was found when the application rate was higher than 220 kg·hm-2.The accumulated amount generally increased with rate increase.Total nitrate-N amount leached below 100 cm soil depth ranged from 406 to 882 kg·hm-2 after three wheat-corn seasons when application rate was from 220 to 550 kg N per season.In the winter season,nitrate-N did not leach into soil layer below 100 cm depth,where optimized water was applied to wheat using sprinkling irrigation system.However,in the summer maize season,there was great nitrate-N leachout of 0~100 cm soil layer due to strong rainfall.N rates did not affect wheat and corn yields in the first year but significantly affected crops yields in the following two years,he yield could increase significantly when nitrogen application rate was 110 kg·hm-2 per season compared to treatment with no nitrogen application,there was no significant increase in yield when nitrogen application rate was more than 330 kg·hm-2 per season.Nitrogen use efficiency decreased sharply when nitrogen application rate was more than 220 kg·hm-2 per season.Considering economic benefits(crop yield) and environmental benefits(nitrate-N leaching),nitrogen application rate of 110 kg·hm-2 per season was recommended for wheat and maize cultivation in Beijing.