EFFECT OF LEACHING IRRIGATION ON THE SPATIAL DISTRIBUTION OF SOIL SALINITY IN THE HETAO IRRIGATION DISTRICT IN CHINA

摘要

To evaluate the effect of leaching irrigation on the spatial distribution of soil salinity, an electromagnetic induction method (EIM) was used to track the salt dynamics of poorly drained fields during leaching irrigation in the Hetac irrigation district. In a 0.3-ha study area, we observed soil salinity and micro-topography at over 700 points, and the groundwater level and salinity at 17 points, between 2002 and 2003. Spatial analysis was used to determine the inter-relationships of soil salinity, irrigation water path, and groundwater. Aftei leaching irrigation, soil salinity in the root zone was reduced temporarily. During the observation period, the distribution of soil salinity did not change greatly. Lateral flow of groundwater was quite slow and there was little difference in groundwater salinity before and after irrigation. There was a good correlation between groundwater salinity and soil salinity. The distribution of soil salinity was largely affected by the micro-topography of the field. As there was very little lateral movement of groundwater in this field, leaching irrigation enhanced only the vertical movement of salt in the root zone and did not reduce the heterogeneous salinity distribution in groundwater, which remained a potential salinity hazard. The heterogeneous distribution of groundwater salinity was attributed to the uneven distribution of irrigation water owing to poor land leveling. The results suggest that leaching irrigation is not efficient foreliminating soil salinity problems in poorly drained areas. The heterogeneous distribution of soil salinity may be reduced if land is leveled more carefully. Nevertheless, the main constraint remains the lack of drainage in such areas. There is an urgent need to classify the entire Hetao irrigation district according to how well areas are drained and to determine the fundamental movement of groundwater and salinity on a large scale.