Study Of Soil Water Characteristics In Loess Hilly-Gully Region Of Yanan

In this paper, the changes of soil water storage within five years were analyzed, the variations of time and space of soil water were elaborated systemically, and study on the water requirement rules of crops by determining 0～180cm soil water storage of shady slope, sunny slope, semi-shady and semi-sunny slopes, different position of valley lands. Which provides some scientific theory foundation for ecological water use and reasonable collocation of vegetation in Loess hilly-gully region, improving the high yield and quality of crops and apples in dry land, restoring natural forests ecological engineering. Main result as follows:1. The change of soil water was fluctuant from 2001-2005, it was slow from the beginning of November to the end of June next year. Soil water changed rapidly from July to September, and changed slowly again from September to November. Seasonal characteristics of soil water showed within a year: Winter soil storage>Spring soil storage>Autumn soil storage>Summer soil storage.2. Space variation characteristics showed different soil water storage with different slope. Soil water storage changed with slope aspects varied. In vertical change, soil profile of terrace field can be divided into 3 levels: soil water abrupt changing layer(0—40㎝), soil water of which changed greatly affected by rainfall, evaporation and crop utilization, and most unstably. Soil water active layer (40—100cm), which was main distribution and water accepting layers of crops and vegetation roots, and was main water-supplying sources and water reservoir of crops and vegetation growth, soil water changed disorderly affected by crops roots. Soil water relatively stable layer(100—180㎝), which was distribution layer of crops deep roots, the amount of soil water changed a little.3. Rainfall is the main factor affecting soil water change in Loess hilly-gully region, the change of soil water was hysteretic relative to rainfall, they were asynchronous. Whatever slope, the sequence of soil water storage was downside part>middle part>upside part. Annual variation amplitude in same part of soil water was upper sunny slope>semi-shady and semi-sunny slope>shady slope. Soil water of four land use types were natural forest>farmlands>orchard>natural grass land. In 0～40㎝ soil water abrupt changing layer, soil water variation amplitude of farmland, orchard, natural grass land and nature forest were not same every year, no regularity. Soil water in 40㎝～100㎝ soil layer changed regularly, the sequence was nature forest>farmlands>orchard>natural grass land.4. Soil water satisfaction condition of different crop was different, Water shortage degree on upper slope of nature forest from November of 2001 to October of 2005 varied greatly, no regularity. Water satisfaction degree in different parts of corn field was 100% only from November of 2001 to April of 2002, it was water shortage in the other months. In orchard, soil water was not short only from October of current year to March of next year. It was concluded that there was a close relationship between water consumption of apple and soil water, rainfall time distribution after studying the water consumption rule of orchard and corn field in dryland. The amount of water consumption was bigger when apple grew under abundant irrigation, which was smaller when apple grew under deficit irrigation. The reason of leading to water shortage of apple was annual rainfall unevenly distributed. Water consumption laws of corn and apple were same, crops water consumption had no direct relation with rainfall, but connected closely with soil water and rainfall distribution.