| In recent years, much attention has been focused on the land use/cover change at various scales. Land use/cover change may influence soil water and soil nutrients, as well as various material cycles. The Loess Plateau is very serious in soil erosion and water loss and is one of the key regions for eco-environmental construction. Much effort on soil erosion control and ecosystem restoration has been made in recent years, especially the project of"Conversion of Farmland to Forest and Grassland Regeneration", which initiated in 1999 and carried out in 10 provinces including 363 counties located in mid- and western China. Extensive vegetation restoration was implemented and land use/cover has changed during the 8 years since this program started. The paper mainly considered the soil-water environmental effects of revegetation on the Plateau. The primary study area of this project was the crisscross area of wind-water erosion in the north part of the Plateau. Liu Daogou watershed was the representative small watershed for the severely degraded ecosystems in this area. Through two years field observations, the effects of land use and its patterns on soil moisture, soil water-physical and nutrient properties, successional characteristics of vegetation community, eco-hydrological cycle and runoff and erosion were studied in plot, slope, and small watershed scales. The results are as follows:1. The mixed land use structures formed the patterns of plaque mosaic with different soil moisture in the slope, which was helpful to slope runoff and erosion controlling. In the small watershed, soil moisture presented moderate variability, and had obvious spatial structures, which could be described by Gaussian models. Compared to the moist condition, the soil moisture had higher sill and range, but lower nugget-to-sill ratio under dry condition, indicating that precipitation could change the intensity of soil moisture variability and the distribution structure. We constructed the spatial regression-prediction models of soil moisture. In these models, land uses and soil attribution variables could synthetically explain 78.7%-86.5% of the soil moisture spatial variability under dry condition; but under moist condition, integrated the land uses, soil texture and topographic variables could only explain 58.2%-77.7% of the variability. The models had small mean prediction errors (MPE) and root mean square prediction errors (RMSPE), which could be used in the research region to predict soil moisture.2. Mixed land uses patterns developed by the spatial arrangement of different land uses could trap the runoff and sediments, which ultimately formed the plaque mosaic patterns of soil physcical and chemical properties on the slope. Except for soil bulk density in the small watershed, soil physical and chemical properties presented moderate variability, and had moderate spatial autocorrelation. These spatial variabilities could be controlled by intrinsic variations in soil characteristics (texture, mineralogy and soil genesis processes) and extrinsic variations (soil fertilization and cultivation practices). The study built the spatial multiple regression-prediction models of soil properties. There were different variables entered to the different soil properties prediction models, which meant that at different soil depths, there were different environmental factors controlled the spatial variabilities of different soil properties. The results suggested that creating a mosaic pattern to increasing spatial variation of areas by land use arrangement to trap soil nutrients to stay in the ecosystem and more nutrient matter input such as manure addition and crop residues return would improve the soil quality effectively on the hilly area of the Plateau.3. Kriging interpolation represented that soil surface moisture and bulk density in mixed land-use structure plot had apparent characteristics of plaque mosaic pattern, which were uniform with land-use structures and easy to form self-regulation system of runoff erosion. M1 plot (korshinsk peashrub-mung bean-alfalfa) had the smallest annual erosion modulus, and the erosion reduction rate in the research two years reached to 98% and 94%, respectively. With regards to the control of erosion, this study suggested two practices for land management, i.e., creating a mosaic pattern by land use arrangement and raising the soil infiltration capacity within the spatial mosaic pattern.4. Alfalfa yield increases for about seven years after seeding, then, it declines and alfalfa is replaced by a natural community, dominated by stipa bungeana, that begins to thrive about ten years after seeding with alfalfa. Soil bulk density increases over time and soil water is severely depleted under alfalfa. The decline in alfalfa yields is most likely related to water stress resulting from depletion of soil water at deeper depths of the soil profiles, rather than by competition from native species. Restricting the plant density could reduce water consumption by alfalfa; while soil water recharge may be facilitated by rotating alfalfa with other crops, natural vegetation or by leaving the soil bare for more than three years before replanting.5. In the study site, the average canopy interception rate of korshinsk peashrub was 24.2%, and the steady interception rate was about 12%. The average interception rate of apricots canopy with"Funnel"shape was 15.1%, at the same time the steady interception rate was about 10%. Compared to farmland, the erosion reduction rate of stipa bungeana land, korshinsk peashrub land, apricot land and fallow land were greater than 80% in 2007. Gray correlation analysis suggested that vegetation coverage and plant height were the the important factors affecting the runoff and sediment production on sloping land, whose gray correlation degrees all exceeded 0.5. The soil moisture in a profile was greatly affected by different land uses and soil texture. At top layers for every plot, soil moisture varied seasonally, but with the increase of soil depth, these variations were reduced. The soil moisture in the soil profiles showed a"consumption-compensation"seasonal process in korshinsk peashrub and apricot land. The soil water storage in 0-120cm was apricot> korshinsk peashrub in sandy loess soil> korshinsk peashrub in loess soil> korshinsk peashrub in hard loess soil> korshinsk peashrub in sandy soil. The soil water storage didn't show obvious seasonal changes with small effect of rainfall at 120-400cm soil depth. The soil water storage in 120-400cm was apricot> korshinsk peashrub in sand loess soil> korshinsk peashrub in hard loess soil > korshinsk peashrub in loess soil> korshinsk peashrub in sand soil. 4-6 years old M.sativa used more water in 0-400cm soil layer, and the soil moisture consumption of the top layer by the shallow root herbage in fallow land was greater than in crop land by bean.6. The water balance of different land uses indicated that the soil water kept balance for the each plot over the whole study period. There was a slight surplus in soil water storage during the end of the observation period on each land use, especially farmland, which had the highest surplus, being 106.9mm, and the average evapotranspiration/precipitation (ET/P) was 71.0%. In each experimental year, the soil water balance condition had small difference among the land uses. Korshinsk peashrub in loess soil and in sand soil and the alfalfa (I) grown on loess soil in 2008 had more evapotranspiration than precipitation in the study period, and ET/P were 103.2%, 102.5% and 104.6%, respectively. In the end of the observation period, soil water storages were in negative balance. The simulation of water flow by SWAP model represented that the predicted values of soil moisture and soil water storage had obviously consistent with the measured values. The water input on stipa bungeana grassland was roughly equal to the output. The water output on alfalfa grassland was 1.38 times of that on cropland, and the evapotranspiration of alfalfa was 3.88 times of that on cropland with mung bean, which was the main reason causing soil water deficit on alfalfa grassland. So conversion of farmland to forest and grassland regeneration will increase the output of water in the SVAT system, if there is a great deal of water consumption by vegetation community, it will lead to soil desiccation.Based on a small watershed, the studies of the soil-water environmental effects of revegetation evaluated the project of"Conversion of Farmland to Forest and Grassland Regeneration"in the Wind-water Erosion Crisscross Zone, but also could be as recommendation for revegetation practice. In this paper, issues related to the soil-water environmental effects including temporal-spatial variability of soil moisture, soil-water physical and nutrient properties under the effect of land use and its patterns, successional characteristics of vegetation community and their relationships with soil-water physical properties under vegetation construction processes, the water flow of soil-vegetation-atmosphere-transport and its consumption characteristics of the representative sparse vegetation in the region are analyzed. Hopefully, the paper could be of some importance for both the basic research of soil variability, water cycle of SVAT system and practical application of vegetation restoration. In the future, more accurate modeling of ecological processes should be done by taking the characteristics of temporal-spatial soil variability based on land use patterns into consideration.
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