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

1)在对巴基斯坦旁遮普省地下排水工程(包括第四排水工程)进行实地考察的基础上，明确了旁遮普省平面排水的特点。一个地下排水系统单元的特点是利用一个泵将收集到的排水从水池中排出，通过下排水，并由于地形平坦将排水管收集到排水渠中。(2)在一种利用排水的深灌的平静试验中，显示了淡水的高效利用，但也出现了盐分问题。因此，有必要采取缩短和转移排水用水时间等措施。3)通过旁遮普省田间试验，确定连续排水灌溉显著降低了小麦籽粒产量，加速了农田盐碱化。在三年的连续试验中，…普通土壤退化为盐碱地，盐碱度增加。但第一年试验减产幅度有限，土壤Ece增幅不大，建议通过合理细致的水分管理措施，如每年有效淋盐、渠水与排水循环灌溉、渠水与排水混水利用等，来控制上述问题。4)通过对咸海盆地的实地研究，得到了稻田饱和土层中盐分行为的显著发现。深层的盐分在渗滤水中向上扩散，从而在底土饱和后增加了浅层土壤的水分盐分。这一发现驳斥了这样的假设，即在干旱地区种植水稻有效地淋洗了土壤中已经积累的盐分。由于稻田渗漏水通过农田排水层下面的区域移动，加速了邻近旱地地下水位的上升和盐分的积累。因此，在灌区实行轮作制度的水稻和旱地作物混作加剧了旱地的内涝和盐分积累。较少

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