[NO3(-)-N dynamics in a spring wheat and radish multiple-crop system in the Hetao Irrigation District]

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 approximately 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 non-fertilizer 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.