| Soil nitrate accumulation is often occurred because of excessive nitrogen fertilization which easily leads to groundwater and vegetable nitrate pollution, which does great harm to people's health. The Urgent way to solve the pollution is to reduce or eliminate the nitrate accumulation, nitrate migration, nitrate leaching, and nitrate leakage.According to Ecological Niche Theory, in intercropping systems different crops occupy their own niche to reduce the competition, which helping root growth and development. Different crops nutrients uptake happened in different soil regions because different crop have different root depth and distribution area, then they can utilize the nitrate in different soil depth. By this way, it can not only improve the utilization of fertilizer, but also can reduce the new accumulation of nitrate in soil. In this paper, vegetables with different rooting depth were intercropped together, to study the effect on temporal and spatial dynamic of soil nitrate, and the vegetables nitrate concentration.In this study, two vegetable intercropping systems were selected by field experiments. The radish (with deeper root) and celery (with shallow root) were selected to intercop as the first season crop, the eggplant (with deeper root) and shallot (with shallow root) as the second season crop. And in the second corp sysetem we added reducing fertilization measure.The nitrate content were measured in the crop harvest stage in order to show the law of the nitrate migration and accumulation in the 0-100cm depth soil layers. And the soil nitrogen balance was calculated to provide a optimized cropping systems with high economical income and a environment friendly with low non-point source pollution risk.The main conclusions of this study were as following:1. The whole experiment showed that the nitrate content in the intercropping system decreased compared with the monoculture system, but the total N increased on another hand; At the same time, the nitrate content decreased in the fertilizer optimizing treatment in shallot compared with the conventional treatment, but the total N content increased.2. Deep root crop is in a dominant position compared with the shallow root crop. There is a significant yield-increasing on deep root crop and there is a yield-decreasing on the shallow root crop, but it is not significant. Both types systems showed the inter-cropping advantage.3. The result of the first crop showed that the nitrate content increased in the surface soil layer and decreased in the deep soil layer not only in early growth period but also in the harvest time. The upper soil nitrate accumulation under the conditions of inter-cropping was higher than monoculture one, but the nitrate amount in the lower soil profile is opposite. The total accumulation amount reduced 1.4%, 9.9% in the conditions of inter-cropping than the monoculture, respectively.4. The results of the second crop showed that the nitrate accumulation and migration of the inter-cropping areas are high than the monoculture under the normal fertilizing level conditions, which showed that the conventional treatment using excessive nitrogen in this experiment, which left a large number of residual nitrogen in the soil.5. The results of the second crop showed that the nitrate accumulation and migration of the inter-cropping areas are less than the monoculture under the fertilizer optimizing conditions, the total nitrate accumulation in the 0-100cm soil profile had the same trend at any stage. It showed that inter-cropping block nitrate leaching effectively, and it reduce the amount of nitrate, too.6. The results of the second crop showed that under the conditions of intercropping cultivation mode, fertilizer optimizing treatments reduce the nitrate content in soil, especially in the deep soil layer; The nitrate content is lower than the conventional fertilization area significantly during the whole growing period; The nitrate accumulation of the fertilizer optimizing area is also lower than the normal one in the whole soil profile.7. Totally: the apparent loss of nitrogen can be reduced by using intercropping or fertilizer optimizing mangement. |
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