| The Tableland of the Loess Plateau is facing with severe soil erosion, vegetationdegradation and the fluctuation of crop yield that resulted from rare precipitation withirregular distributions and unreasonable land use. Making a further understanding of soil andsediment process at watershed-scale is fundament for soil erosion and water cycleinvestigations and at the same time can contribute to the stabilization of crop yield. This studyinvestigated soil water dynamics and capabilities of runoff generation and sediment transportin different vegetation covers in the tableland and gully regions of Wangdong watershed bymonitoring soil water in soil plots, vegetation covers and sediments in the tableland and gullyregions, coupled with soil physical properties measurments under laboratory condition. Themain conclusions could be given as following:（1） Soil type in the tableland of Wangdong watershed was loamy clay soil and in gullyregion it was sandy loam soil. Under different land uses, soil bulk density and saturated watercontent showed weak variations and saturated water conductivity was middle even strongvariation. van Genuchten model could simulate soil water curves in different depths underdifferent land uses/vegetation covers in the gully region with high accuracy.（2） There were differences in soil water use in different land uses in the tableland region.The water consumptions of different vegetation types showed obvious differences in the gullyregion. The gray correlation analysis could describe the tendencies of soil water dynamics indifferent depths, months, and agricultural land uses. It could be seen from the gray correlationcoefficient between precipitation and soil water in different depths that the correlationincreased with depth. The gray correlation coefficient between surface soil water and deepsoil water showed that seepage of surface soil became weak with increasing depth. Soil watercorrelation coefficient at different months indicated that changing status in soil water at Mayand June was mostly close to April and the correlation of the changing status was weak in July,August and September but it increased obviously in October.（3） Runoff coefficient and runoff amount in wheat land were higher than corn and fallowlands in the tableland region. Slope length and gradient had significant effects on them. When the length of soil plots changed from50m to20m, runoff coefficient increased by3-7times.When slope gradient increased from0.5°to1°or3°, runoff coefficient increased by2-4timecorrespondingly. Under different land uses/vegetation covers in the gully region, runoff wasamong2.48-5.82m3ha-1. The runoffs of different land uses showed a decline order as:P.orientalis Franco, R.pseudoacacia L&H.rhamnoides, P.orientalis Franco&R.pseudoacaciaL, R.pseudoacacia L, P.tabuliformis&R.pseudoacacia L, P.tabuliformis, P.tabuliformis&H.rhamnoides Linn, Grassland, H.rhamnoides Linn. Erosion modulus was among0.27-1.18tkm-2and its changing tendency was as same as runoff. From2008to2011, the efficiencies ofwater conservation for different soil plots showed a decline order as: Grassland,P.tabuliformis&H.rhamnoides Linn, H.rhamnoides Linn, R.pseudoacacia L&H.rhamnoides,R.pseudoacacia L, P.tabuliformis&R.pseudoacacia L. Water storage in grass land was thehighest and at the same time was stable. The forest of H.rhamnoides Linn mixedH.rhamnoides Linn worked well on soil and water conservation, indicating returnng farmlandto grass and forest could improve regional soil water storage efficiently.（4） There were great differences in runoff and soil erosion for different land uses/vegetation covers under a rainfall event. Runoff in the gully was much high than the tablelandwithin the same year. And sediment and erosion modulus showed certain of complicationowing to being affected by land use. The maximum runoffs in the tableland and the gullyregions presented at the middle-late stage of rainfall season and the maximum soil erosionappeared at the early stage of rainfall season in Wangdong watershed. |
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