RESEARCH ON MEASURES TO PREVENT SECONDARY SALINIZATION AND FARMLAND CONSERVATION USING MATERIAL AND WATER CIRCULATION IN THE LOWER LOESS PLATEAU AREA

研究区主要的盐渍化过程是：1.毛管水位上升；2.利用咸水灌溉；3.倾倒和压实田间沉井挖土；4.地表地形和排水条件的变化；5.偶尔的内涝，加速下层沉积的钠的溶解，从而增加地下水的SAR。分析了造成这些过程的原因：1.地下水位高，2.地下水含盐量高，3.下垫层溶解盐分沉积，4.低层不透水，5.渠道渗漏损失严重，农田渗漏损失大，6.地下水管理不力，7.排水管理体制不健全.在地下水位较深的井中，经常出现低EC值、高残留碳酸钠(RSC)的现象。因此，在持续利用…地下水的情况下，土壤的碱化程度可能会增加更多这些井是用来灌溉的。根据一系列研究结果，提出了防治盐碱化的建议：1.通过设置有效的排水系统降低地下水位；2.控制田间倾倒的盐渍土；3.管理咸水灌溉用水；4.维护和运行排水系统以发挥其功能；5.采用淤地膜复垦盐碱化农田；6.沿渠和农田周围引入生物排水，以防止内涝。指出了黄土高原淤泥质径流水改良盐碱地，提高土壤肥力，提高土壤物理性质(质地、孔隙度、渗透性)，利用黄土高原侵蚀土壤(有效利用同一流域物质循环)，减轻渭河、黄河流域悬移质输沙量的优点。较少

The identified main salinization processes in the study area are due to : 1. capillary water rise ; 2. use of saline irrigation water ; 3. dumping and compacting dug soil of well sinking in the field ; 4. variation in surface topography and drainage condition ; 5. occasional waterlogging, which accelerates dissolution of deposited sodium in the subsoil layers, and afterward increases groundwater SAR. Causes bring on these processes are identified : 1. high groundwater table, 2. high groundwater salinity, 3. deposition of dissolved salts in subsoil layer, 4. impermeable soil layer in lower layers, 5. heavy seepage losses through canal and percolation losses in farmlands, 6. insufficient groundwater management, and 7. insufficient drainage management system. Frequent occurrence of low EC value with high residual sodium carbonate (RSC) was observed in wells with deep groundwater table. Thus alkalization of soil is likely to be increased under the continuous utilization of groundwater from … More these wells for irrigation. Based on a series of research findings, some suggestions for preventing salinization processes are proposed : 1. lowering the groundwater table by installing effective drainage system, 2. controlling dumped saline soil in the fields, 3. managing the use of saline irrigation water, 4. maintaining and operating drainage system to fulfill its function, 5. applying warp soil dressing to reclaim salinized farmlands, and 6. introducing biological drainage along canals and around farm lots to prevent waterlogging. Merits of warp soil dressing applying muddy runoff water containing eroded soil from Loess Plateau are identified : 1. improving saline soils (through soil dressing ＆ leaching), 2. improving soil fertility, soil physical properties (soil texture, porosity, permeability), 3. utilizing eroded soils from Loess Plateau (effective use of material circulation in the same watershed), and 4. mitigating suspended sediment load in Wei River and Yellow River Basins. Less