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

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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