河套灌区春小麦-萝卜复种模式下土壤NO_3^--N动态

NO_3^--N Dynamics in a Spring Wheat and Radish Multiple-Crop System in the Hetao Irrigation District

研究了河套灌区春小麦-萝卜复种模式下,土壤、土壤溶液和地下水NO3--N浓度的动态变化.结果表明:随着试验时间的延长,土壤表层NO3--N含量降低,深层(100~150cm)增加;土壤溶液中、下层NO3--N浓度(70、120cm)显著高于上层(30cm),尤其是在萝卜生长季.当前的灌溉条件下,不同年度、不同生长季土壤NO3--N淋失量的多少与土壤水分的下渗量密切相关,且输入的氮素中有30%以上以NO3--N的形式淋失掉.施肥区地下水NO3--N浓度显著高于未施肥区,且65.5%的水样超过WHO规定的上限(11.3mg/L).总之,经过连续2a的春小麦与萝卜复种可使表层土壤NO3--N含量明显降低,但由于中、下层土壤剖面中残留大量的NO3--N,因此在当前灌溉措施下,短期内NO3--N淋失是不可避免的.

The NO3^--N dynamics of the soil, soil solution and groundwater were studied under spring wheat and radish multiple-crop system in Hetao Irrigation District over two years. A strong tendency of NO3^--N to move from upper layer to deeper layer could be observed and soil NO3^--N was increased at the layer of 100 - 150cm. NO3^--N concentration of soil solution at the depth of 70 and 120 cm was significantly higher than that at the depth of 30 cm, especially in the radish growth season. NO3^--N leaching amount was correlated with deep percolation at both different crop growth seasons and different years and it accounted for higher than 30 % of total N input across two years. In the fertilizer plot, the concentration of NO3^--N in groundwater was far higher than that in the nonfertilizer plot, and 65.5 % samples were over the safe standard of WHO （11.3mg/L） in the fertilizer plot. The topsoil NO3^--N content was markedly decreased during the two years multiple-crop system. However, NO3^--N leaching was inevitable in the near future due to a large amount of residual NO3^--N in the middle and deeper soil profiles.