Salt behavior in soil affected by groundwater management and reuse of drainage water using subsurface drainage system

1）通过对巴基斯坦旁遮普省地下排水工程（包括第四排水工程）的实地调查，明确了旁遮普省平面排水的特点。地下排水系统的一个单元的特征在于，由于地形平坦，利用泵将集水池中收集的排水通过暗渠和收集排水管排出到排水渠。2）在静水试验中，一种利用排水进行地下灌溉的方式，表现出较高的淡水利用效率，但也存在盐分问题。因此，有必要采取措施，如缩短和转移排水应用的时间。3)通过在旁遮普进行的田间试验，确定了连续排水灌溉显著降低了小麦产量，加速了农田盐渍化。在连续三年的实验中， ...更多信息 t时，普通土壤退化为盐渍土，土壤碱度增加。但第一年试验减产幅度有限，土壤电导率增加幅度不大。因此，通过合理的水分管理措施，如每年进行有效的排盐、渠水与排水循环灌溉、渠水与排水混合利用等，可以控制上述问题。4)通过对咸海盆地稻田饱和土层盐分动态的现场研究，获得了显著的成果。当下层土壤饱和后，深层土壤盐分向上层扩散，增加了浅层土壤水的含盐量。这一发现驳斥了在干旱地区种植水稻可以有效地沥滤土壤中已经积累的盐分的假设。由于稻田中的蒸发水通过排水床以下的区域，加速了邻近高地地下水位的上升和盐分的积累。因此，以水旱轮作为基础的水旱混种加剧了高地的涝渍和盐分积累。少

A series of research can be summarized as follows :1)Based on the field survey of subsurface drainage projects in Punjab Province, Pakistan, including Fourth Drainage Project, the characteristics of drainage in the Punjab Plane were made clear. A unit of subsurface drainage system can be characterized by the utilization of a pump to drain collected drainage water in a sump through underdrain and collecting drain pipes off to a drainage canal due to flat topography. 2)In a calm experiment for a kind of sub-irrigation utilizing drainage water, high efficiency of fresh water use was displayed, however, salinity problem arose. Thus necessity of measures, such as shortening and shifting of the duration for drainage water application, was suggested. 3)Based on the on-site experiment in Punjab, it was ascertained that the continuous irrigation with drainage water significantly decreased the wheat grain yield and accelerated the farmland salinization. During the three year continuous experimen … More t, the ordinary soil degraded to saline soil and increased its sodicity. However, the reduction of yield was limited and soil ECe showed little increase in the first year experiment, so it is suggested that the above problems can be controlled by the careful and proper water management practices, such as the effective *eaching of salt every year, application of cyclic irrigation with canal water and drainage water, and utilizing blended water of canal water and drainage water. 4)Based on the on-site studies in Aral Sea Basin, a remarkable finding was obtained on the salt behavior in saturated soil layers of rice fields. Salts from the deeper layer diffused upward in percolated water and thus increased soil water salinity in the shallow layer after the subsoil was saturated. This finding refutes the hypothesis that rice cultivation practiced in arid areas is effective for leaching salts already accumulated in the soil. Because of the movement of percolated water from rice fields through the zone below the field-drain bed, the rise of the groundwater table and salt accumulation were accelerated in the adjacent upland fields. Thus mixed cropping with rice and upland crops based on the crop rotation system in an irrigation block exacerbated waterlogging and salt accumulation in upland fields. Less