Study On Soil Physical Characteristics And Hydrological Characters Of Diediegou Small Watershed In Liupan Mountains

To select and determine the strategy with the status of water resource is the key point in ecological reconstruction and vegetation restoration in the semi-arid zone of Northwest China, of which the hydrological characters of soil is one of the most important factors in its progress. The Liupan Mountains, known as the famous water-retention area and mountain ecosystem in the semi-arid zone, is selected for studying the hydrological characters of soil in order to provide a theoretic basis for ecological reconstruction and vegetation restoration.In this study, the soil physical characteristics in 93 plots and the soil moisture in 57 plots, which is in diediegou watershed in Guyuan country of Ningxia province, were observed in the field. The results are shown as below: 1. The variation of soil physical characteristics in the watershedBased on many field investigations, the variation of soil physical characteristics with soil depth, slope aspect, slope position, and vegetation types within the diediegou small watershed. It demonstrate that: the soil bulk density and stone content increase where as total porosity, capillary porosity, non-capillary porosity, saturated water content, capillary soil water content, and field capacity of soil decrease with soil depth.All the soil physical properties measured in this study are the best on the south slope than other slopes. With lowering slope position, the soil thickness, bulk density, stone content, and non-capillary porosity decrease;while the total porosity, capillary porosity, and all water-holding capacity indicators decrease gradually.By comparing the averaged soil physical properties of upper soil layer (0~30cm) among four main vegetation types, the sequence of soil bulk density is the old field>the woodland>the grassland>the shrub land. On the other hand, for the total porosity, capillary porosity, saturated soil water content, capillary soil water content, and field capacity, that are: shrub land>grassland>woodland>old field as well. The stone content of soil in the abandoned farmland is the least, and there is less difference among all others land types. For the non-capillary porosity, its order from high to low is abandoned farmland, woodland,shrub land, and grassland.Finally, the regression equations of soil physical properties with longitude, latitude, altitude, soil aspect, slope gradient, slope position, soil depth, and ground vegetation coverage were established, respectively.2. The of soil hydrological functions in the watershedThrough observe to the soil water-holding capacity in different land-uses, the highest is the old field (964.45t/hm2). For it's in different slope, their order from high to low is the north slopes (755.60 t/hm2), the semi-sunny slopes (742.57 t/hm2) and the south slopes (436.85 t/hm2). In all the slopes, it increases with situation decrease, in the term of the soil depth adding. But it's out of the way in the midst or lowest because of the human disturb.The result of soil infiltration rates in different vegetation types in the small watershed measured by in laboratory shows, The rank as: Natural Ostryopsis davidiana shrub (1.91mm/min)>Laru principis-rupprechtii wood-land (1.42mm/min)>natural grass-land (0.95mm/min)>natural Hippophae rhamnoides shrub(0.49mm/min). Due to the effects of human disturb and vegetation, the rank of soil soil infiltration rates in different slopes from high to low is the middle the top and the low;but for the soil types, their order from high to low is the cultivate Loess, the Loess and the old red soil.Four models in Diediegou watershed verified all the soil infiltration rates, of which the Horton infiltration model was better than the others. Finally, the regression equations of the steady soil infiltration rates with the non-capillary porosity, stone content and the total porosity were established, respectively.3. The variation of Soil moistureThe soil moisture and rainfall in the area express the synchronization, the soil moisture increase after big rainfall and decrease if there is no rainfall in a long period. According to the soil moisture dynamic characteristic in growth season, four periods of moisture change are divided, the consume period, the accumulate period, the fade period and the stable period. And the soil moisture change is different in different depths: it is violent in surface layer but middle in the depth layer. Four-change layer are separated: the fast change layer (0-20cm), the activity layer (20-60cm), the relative activity layer (60-120cm) and the relative stable layer (below the layer of 120cm).In the watershed, the spatial variation of soil moisture is very distinct among different slopes, which can list from lower to higher: the South Slope (15.43%) < the semi-sunny slope (16.10%) the Ostryopsis davidiana shrubs on semi-shade slope (23.8%)>the abandoned farmland (23.7%)>the Larix principis-rupprechtii wood-land in shade (22.9%)>the grass-land on semi-sunny slope(21.8%)>the farmland(21.0%)>the grass-land on south slope(17.3%) > theHippophae rhamnoides shrub on semi-sunny slope(16.5%).It suggest that: the natural vegetation is the best type for holding water in the watershed, on the other hand, if the farmland was abandoned, the soil water holding capacity would increase.Smoothly the results suggest that the soil water in different vegetation types exhibit the status of below available inmost time And the vegetation types in the watershed can be rated by soil moisture availability as: natural grass-land > the Hippophae rhamnoides shrub on semi-shade slope>the Pntnus davidiana springwood on mesa >the Larix principis-rupprechtii wood-land in shade> the Ostryopsis davidiana shrubs on semi-shade slope> the Hippophae rhamnoides shrub on semi-sunny slope> the mixed shrubs on semi-sunny slope> the Larix principis-rupprechtii wood-land on semi-shade slope.