Studies on Effective Desalinization Methods from Soils

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In this study, we made two strategies for improving desalinization of saline soils. The one is applying soil drying before leaching and the another is mixing soil amendments for stabilizing percolating pores. The two strategies were examined on saline soils, the bottom mud of Kojima lake, Isahaya polder soil and soil of Hetao Irrigation District, Inner Mongolia.Mechanism of promotion of salt dissolution by soil drying was studied with special attention to air slaking of the soil matrix. Salt dissolution was promoted not only by salt accumulation to the surface of soil matrix but also by increasing salt diffusion coefficient through stabilized soil structure due to the soil drying. The experimental results showed the maximum salt dissolution at the water content of the maximum air slaking. Soil drying to the water content of the maximum air occurred slaking was found to be the most effective.It is known that the percolation pores are logged and leaching efficiency decreases in course of leaching. Soil amendments were added to improve hydraulic conductivity by stabilizing percolating pores. Among the soil amendments tested, the organic compost and the crashed charcoal were found most effective. The effectiveness was small on the Isahaya soil than the Hetao soil, because of swelling and dispersive properties of the Isahaya soil. Gypsum showed remarkable effect both on maintaining hydraulic conductivity and on extrusion of sodium.Soil drying practice, in particular, full upside down plowing was found to be very effective on desalinization and soil maturing of the Isahaya polder through successive yearly field research. Surface soil extrusion method, sand drain method and gypsum application method are tested and their effectiveness was evaluated by field test in Hetao Irrigation District.