SOIL WATER HOLDING CAPACITY AND SOIL AVAILABLE WATER IN PLANTATIONS IN THE LOESS REGION Study on Soil Capacities of Water-retention on Typical Vegetations in the North Side of Liupan Mountains in Ningxia Studies on Soil Water Characteristic Curves and Infiltration Capability of Maowusu Sandy Soil Water Consumption of Single-Tree from the Main Afforestation Species in Western Shanxi of Loess Area