Study On Salt Accumulation Characteristics Of Layered Soil Under Drop Water Condition

The infiltration experiments were conducted based on the soil columns with different layered soil structure to research the retardation effect of layered soil with clay interlayer to the salt transfer under drip irrigation, and the experimental results were compared with the retardation effect on the homogeneous soil columns. The loose sand and light loam were used in homogeneous soil columns, and loose sand with light clay interlayer(LSLCI) as well as light loam with light clay interlayer(LLLCI) were used in layered structural soil columns. The experiments were designed to irrigate homogeneous soil columns with water of 1.0L, 1.2L and 1.5L and layered soil columns with water of 2L.Otherwise, in the layered infiltration experiments, the interlayer thicknesses were controlled to 5cm, 10 cm and 15 cm. The interlayer positions were controlled in 30cm-40 cm, 35cm-45 cm and 40cm-50 cm. And there also were double light clay interlayer experiments. The main results get from the experiments are:(1) Clay soil which has weak permeability was used as the interlayer of layered soil would have the retardation effect on water and salt transportation and result in salt accumulation in layered soil. The relative increasing saltation of salinity content existed between desalted area and salt deposition area. It was the upper and lower surfaces of the interlayer. And the bigger the permeability differences of two layers were, the stronger the retardation effect was.(2) The retardation effect of clay interlayer on salt transport was stronger than that of water transport, so that large amount of salt was retarded in interlayer, at the same time, water can slowly infiltrated through the interlayer and into deep soil. And the clay interlayer showed the phenomenon of quasi-semipermeability. The quasi-semipermeability effect was produced by the strong absorbing effect of the interlayer on salt.(3)With the increase of clay interlayer thickness, the retardation effect on water and salt transport was gradually strengthened. When the layered soil was made up of loose sand and light clay which has great permeability differences,the 15 cm thick interlayer only has water insulation and salt storage effect and without quasi-semipermeability effect. The quasi-semipermeability effect of 10 cm thick interlayer was more apparent than that of 5cm thick interlayer. When the layered soil was made up of light loam and light clay which has weak permeability differences, the quasi-semipermeability effect of 10 cm thick interlayer was best.(4)The shallower the location of the interlayer was, the stronger the retardation effect on water was. The salt accumulation amount increased as the interlayer position increased, and the location of salt retardation was deeper and the soil salinization was difficult. In this paper, the salinity increased most when the interlayer was between 35cm-40 cm, that was followed by the interlayer between 40-50 cm, and the finally was the interlayer between 30-40 cm. Among LSLCI and LLLCI columns, according to the position of the interlayers, the quasi-semipermeability effect was ordered: 35-45cm>30-40cm>40-50 cm.(5) In the double clay interlayer soil, the clay interlayers both had a good retardation effect on water and salt. If we regarded the two interlayers and the soil layer between them as a whole, and made a comparison with the single interlayer soil of different thickness. It could be found that, when the layered soil was made up of loose sand and light clay which has great permeability differences, the retardation effect of double clay interlayer soil was equal to that of 10 cm thick single interlayer, and stronger than 5cm thick single interlayer, weaker than 15 cm thick single interlayer. The quasi-semipermeability effect of double clay interlayer soil was stronger than that of 5cm thick single interlayer and weaker than 10 cm thick single interlayer. When the layered soil was made up of light loam and light clay which has weak permeability differences, the retardation effect of double clay interlayer soil on water was more apparent than other three single clay interlayer with different thickness, and the same as the quasi-semipermeability effect.