The Effect Of Different Land Uses On Soil Eco-hydrology Properties In The Semiarid Loess Area

The Loess Plateau region is a fragile ecological environment, and it is also an economically underdeveloped area. The shortage of water resources and the serious desertification seriously restrict the development of the area. With the sustainable development and the policy of returning farmland to forest and grassland, it is necessary to establish a sustainable land use pattern. The research of agricultural history and natural science has proved that the best development type is animal husbandry to the arid of Northwest China. Alfalfa is a kind of artif icial grass, and is called as the king of forage. For a long time, it has been considered as a best choose. Although the results of the project of returning farmland to forest and grassland have been reported in many areas, it has been focused on improving the ecological environment and increasing economic benefits. Water in the Loess Plateau is the key factor to restrict the growth of plants, and soil water availability impacts on plant growth and it is the main index of evaluating plant on soil water utilization degree. In this paper, two experiments w ere done. In the first year, meadow, grassland, wheat and alfalfa were as the experimental objects, field sampling and laboratory method was used to measure water content, soil bulk density, soil water characteristic curve and Chlorine Ion to study the different of infiltration under different land use patterns. In the second years, farmland and alfalfa were as objects, respectively, soil particle size, porosity, bulk density, saturated hydraulic conductivity, field capacity, wilting water content, saturated water content, organic matter, pH, water characteristic curve w ere measured. Comparison of physical properties, chemical properties and soil moisture characteristics to analyzes the diff erences of soil properties of returning farmland to alfalfa to provide the theoretical basis for reasonable vegetation construction and sustainable development.It was found that the correlation coefficient of Van—Genuchten model( VG) was greater than 0.99, the residual was less than 0.005; the correlation coefficient of Gardner model was greater than 0.95, the residual was less than 0.01 in different uses, indicating VG model and Gardner model had good applicability for the study area and the VG model was better.Compared to meadow, grassland and wheat, the water content of alfalfa was signif icantly lower. The fluctuations of matric potentials and total potentials in the meadow over 5m were large and the direction of water movement changed dramatic, total potentials increase with depth indicated that water was moving upward. Total potentials and the direction of water movement above 4m changed dramatic and total potentials was no change almost below 4m in grassland indicating that there was no recharge. The total potentials of shallow zone was greater than the deep zone in the wheat indicating that water was moving downward. Matric potentials and total potentials changed dramatically over the entire cross-section of alfalfa indicating direction of water movement changed frequently. The matric potentials of alfalfa was much smaller than meadow, grassland, and wheat. The alfalfa was drier.The chloride profile under several use patterns was signif icantly different, the chloride concentrations were increase with depth to 691.28 mg/ L in meadow. Chloride concentrations of grassland appeared a large peak at 1m and the value was 2073.38 mg/ L, and it was unchanged under 4m indicating there was no infiltration. After the conversion of natural vegetation to rain-fed agriculture, the deep recharge increased to 2.13 mm/ year, accounting for 0.7 percent of the average annual rainfall. The conversion of farmland to alfalfa had led to chloride accumulation to 4m below land surface.There was no significant difference in the soil bulk density, porosity, soil moisture constant, soil texture, SOC and pH in the whole soil profile, but saturated hydraulic conductivity of alfalfa was significantly higher than farmland(P<0.05), and the water content of farmland was signif icantly higher than alfalfa. The difference of soil bulk density, porosity, soil moisture constant between the farmland and alfalfa was in shallow, but saturated hydraulic conductivity was in deep. In 0-0.2m, the bulk density of alfalfa was signif icantly greater than farmland(P<0.05), the porosity and saturated water content was significantly less than farmland(P<0.05). In 0.2-0.4m, bulk density of farmland was signif icantly higher than alfalfa(P<0.01), the porosity and saturated water content was signif icantly lower than alfalfa(P<0.01); In 1.2-1.4m and 1.4-1.6m, saturated hydraulic conductivity of alfalfa was significantly higher than that of farmland(P<0.05). In the 0-1.8m profile, the saturation moisture content, field capacity, and permanent wilting pointy of alfalfa was higher than farmland. The signif icant difference of water content was mainly up1mFor characteristic of the soil water analysis, it is found that soil holding water ability of alfalfa was higher than that of farmland, but soil water supply capacity and available water content of farmland were better; classification of soil water found, the upper limit of the available water of the study area equaled to soil water content of-0.1bar soil matrix potential which is different from other place of the Loess Plateau. The effective water content and quick action water content of farmland were larger than that of alfalfa, but delayed action water content was same. Specific water capacity curve analysis found, that it changed rapidly near the field capacity and changed slowly in the 50%- 60% of field capacity.