The Influence Of Sand Mixed Or Mulch With Top-surface Soil On Soil Water And Salt Movement

[Object] Soil texture improvemtne by sand addition is tranditional way and one of widely used strategy in soil amendment, and always being pay attention to in the past years in Northwest arid region. However little is knowen about the effects of sand addition on soil water movement and soil salt distribution. In present research, simulating experiments were conducted to study the effects of sand mixed and sand mulch on soil water infiltration, evaporation after infiltration, capillary water movement, process of soil second salinization, phreatic evaporation and water and the characteristics of salt movement after evaporation. Meanwhile, severl soil moisture constants (Soil saturated conductivity, soil saturated moisture, soil capicillty moisture and field water) were also investigated, the impact and mechanisum of sand mixing rate and sand mulching thickness on soil water and salt movemtment were analysied. This study is aim to find a practical and efficient way in increasing water utility efficiency and preventing from soil secondary satilization in layered soil, morever it also provide an profound knowledge about sand mixing rate and sand mulching thickness on soil salt and water movement sand in arid area.[Method]1. Soil moisture constants was determinded in labarotary condition.2. The impacts of mixing rate of sand and sand mulching thickness on soil infiltration characteristics were evaluated by soil cylinder simulating experiment in labarotary condition.3. The influence of sand mixing rate and sand mulching thickness on characteristics of soil evaporation after infiltration and salt distribution in different soil lays were meatured by means of soil cylinder simulating methds in labarotary condition.4. The effects of mixing rate of sand and sand mulching thickness on characteristics of soil phreatic evaporation and salt accumulation in soil profile as well were also analysised by means of soil cylinder simulating methds in labarotary condition.[Results]1.The saturated hydraulic conductivity increased with the increasing sand mixing rate, the relationship between them fitting with exponential function. Soil field capacity, capillary water capacity and saturated water capacity decreased with the increasing sand mixing rate, and the relationship between them fitting with linear function. The non-capillary pororisty decreased with the increasing sand mixing rate varied from 0% to 75%, however, the trend became gradually placid when sand mixing rate beyond 75%. "U" shape figure could be well characterization between drainage rate and sand mixing rate.2. Sand mixed with surface soil has a significant effect on increasing water infiltration capacity, the more mixing rate of sand (except 100%), the greater infiltration capacity obtained, and the higher soil water moistrue under the layer of sand observed. Compared with the method of sand mixed, sand mulching exerted a negative impact on soil water infiltration capacity. Through fitting parameters of Philip infiltration model and Kostiakov infiltration model, it is observed that both infiltration modeles could be used to exhibition the relationship between cumulative infiltration and time, in contrast with Philip model, Kostiakov model showed considerably fitting effect.3. Sand mixed and sand mulch could efficiently inhibit soil evaporation collectively, the more mixing rate of sand and sand mulching thickness, the stronger inhibition effect were founded, and the inhibition capacity is more obvious than sand mixed. The relationship between cumulative soil water evaporation of sand mixed and homogeneous soil and time could be described by the Rose experience function, but the relationship between cumulative soil water evaporation of sand mulch and time could be depicted by the linear function during the continuous evaporation experiment conducted days (20 d).4. Sand mixed had detrimental impact on upper soil capillary water and groundwater supply quantity, which decreased with increasing sand mixing rate, and the relationship between capillary water height and time could be described by the power function.5. The phreatic evaporation was constrained by sand mixed and sand mulch, which decreased with increasing sand mixing rate sand and sand mulching thickness, furthermore the inhibition capacity was weaker under sand mixed treatment than sand mulch. The relationship between cumulative soil water evaporation and time could be described by the linear function under the treatment of sand mulch and mixing rates of 75%,100%. However, the relationship between cumulative soil water evaporation of mixing rates of 0%(check and 0 cm)～50% could be described by the binomial function.6. No matter there has groundwater or not, soil salt strongly accumulated in the top-surface soil(0～1 cm) during the process of second salinization. "C" shape could be exhibit soil salt distribution in soil profile layers under evaporation after infiltration with the treatment of slight brackish water supply. Moreover, "г"figure could be employed to describe the charactistic of soil salt distribution in soil profile with groundwater supply, and the soil EC(0～1cm) increased with increased cumulative phreatic evaporation.7. Both Sand mixing and sand mulching could substantially inhibit top-surface soil salt accumulation. The inhibition capacity increased with the increment of sand mixing rate and sand mulching thickness. Salt distribution showed "C"figure in soil profile under evaporation after infiltration. However, its showed"г"figure with groundwater supply under the treatment of sand mixed and control. Salt strongly accumulated in the top-surface soil layer under the treatment of sand mixed and control, and higher salt content were observed close to layer of sand. No matter there has groundwater or not, the relationship between sand mixing rate, sand mulching thickness and corresponding cumulative evaporation and EC(0～1 cm) could be described by corresponding function.[Conclusion]1.Soil mixed with sand exerted significant impact on soil moisture constant.2.Sand mixed had a positive effect on water infiltration, however, sand mulch had detrimental influence on infiltration.3.Sand mixed and sand mulched both play obvious role on decreasing soil evaporation and salt accumulation of soil surface, relatively, the treatment sand mulched exhibited much more effect than the treatment of sand mixed.