Studies Of Nitrogen Environmental Endurance Of Winter Wheat/Summer Maize Rotation System In North China Plain

The urgent problem in intensive agriculture of China is to seek for nitrogen application technique that could not only get high yield but also alleviate furthest threaten of nitrogen to environment. Selecting the high intensive agriculture area-Huimin country, Shandong province to study as the experiment site, the research analyzed environmental endurance of nitrogen in winter wheat and summer maize rotation system of North China Plain through the field experiments and 15N-labeled microplot experiments.Results showed that the yields of crops would reach to high point when nitrogen application rates were low under current soil nitrogen fertility of North China Plain. Residual nitrate-N in 0-90cm soil layers after crop harvest and total losses of nitrogen fertilizer were increasing with the nitrogen application rate raised, behaving no buffer effect to nitrogen fertilizer. If residual nitrate-N in 0-90cm soil profile after crop harvest controlled below 150kg/hm2N, it could reach the double target with higher yield and environmental safety. At that point, nitrogen application rates could be decreased under 150kg/hm2 N,. Nitrogen fertilizer applied at winter wheat season had the obvious after-effect and after-effect and mineralization of soil nitrogen should be fully considered in summer maize season fertilization. Under farmer traditional nitrogen application conditions, crop yield increment per kilogram nitrogen fertilizer in winter wheat season and summer maize season were 2 kilogram and 3-7kilogram respectively.Under farmer traditional nitrogen application conditions (375kg/hm2N nitrogen fertilizer applied at winter wheat season and 240kg/hm2N applied at summer maize season) , the recovery of fertilizer nitrogen by crops at current seasons for conventional fertilization was approximately 26%, while 29%-32% was lost and 41%- 45% of applied nitrogen remaining at 0-100cm soil profile. The lose rate of fertilizer nitrogen in summer maize season were lower than that of winter wheat season. Remaining was the main way of the fate of fertilizer nitrogen whether in current season or in succession season. Nitrogen fertilizer applied in soil have the significant "carry over" effect.Nitrate-N moved out of 0-90cm soil layers in winter wheat season, and accumulated in 90-180 soil profile. The amount of accumulation was increasing with the nitrogen fertilization rates raised, mass irrigation and Intensive rainfall were the major factors causing soil nitrate-N obviously moving downward in winter wheat season. In summer maize season, nitrate-N was mainly resided in 0-90cm soil profile. The movement of nitrate-N in soil was closely related with precipitation and nitrate-N commonly didn't move out of 90cm soil profile in drought summer maize season.. Results of nitrogen balance calculation indicated that large amount of residual nitrate-N before sowing and mineralized soil nitrogen were the important parts of nitrogen input items, which maybe the primary reason of nitrogen fertilizers not increasing crop yield. Residual nitrate-N before sowing was the main compose of nitrogen surplus in low nitrogen application ratetreatments, and apparent loss was the main part in high nitrogen application rate treatments.