Change Of Soil Quality And Its Regulation In Re-vgetation Ecosystem Of The Loess Plateau

Soil quality is the major index to assess soil production and soil environment quality. In order to meet the requirement of eco-environmental rebuilding and solve the forward problems in soil science, ecology, and environmental science, this study was therefore carried out basing on the previous studies that conducted in the related research field. Through historical data collection, field investigation, and laboratory analysis, we compared the soil qualities in various re-vegetation ecosystems located at different watersheds in the Loess Plateau. Besides, emphasized on the changes of different soil properties, we built index systems for soil quality in various re-vegetation ecosystems. Combined with comprehensive analysis of tempo-spatial changes of soil properties, we recommanded regulation measures for the maintaining of soil quality at different areas in the Loess Plateau. The objective was to make ecological health, to provide scientific evidence and practical guide for the eco-environmental rebuilding in the Loess Plateau. The major conclusions were as follows:(1) Studied the horizontal and profile distribution of soil properties in sloping lands at various re-vegetation ecosystems. Except for soil pH, the major soil properties were higher in 0-15cm soil layer than in 15-30cm soil layer and decreased with soil depth in profiles. The effects of slope positions on soil properties varied greatly with re-vegetation, landforms, slope directions, and ecological process occurred in sloping land. Re-vegetation can improve soil properties and reduce soil pH values. Pinus tabulaeformis forest contributed most to soil properties improvement in Nanxiaohegou watershed, while forestland contributed most to soil properties in Ziwuling region. Soil properties in Caragana Korshinskii forest followed the order of Loessial soil>Xiang Loessial soil >Sand Loess. Soil properties were improved with prolonging of re-vegetation times. Twenty years're-vegetation presented the optimal soil properties.(2) Revealed the relationship among different soil properties at various re-vegetation ecosystems. Except for specific surface area and physical clay in soils, other properties were inter-related significantly. Urase, invertase and alkaline phosphatase activities were correlated with soil physiochemical properties in a significant or very significant way. The results of principal component analysis showed that CEC, pH, organic matter, physical clay, nitrate, ammonium, available phosphorus, available potassium, and C/N ratio can be used as the simplified indexes to indicate changes of soil property at various re-vegetation ecosystems. Additionally, the largest direct and indirect influences of soil properties on soil enzymatic activities are all posed by organic matter.(3) Built soil quality assessing system at various re-vegetation ecosystems in the Loess Plateau. According to the sensitivities of variance coefficients and relative range of soil properties, we found that nitrate, available phosphorus, labile organic matter, urase, invertase, and organic matter can be used as the assessing index, which can evaluate soil quality under various re-vegetation ecosystems in the Loess Plateau. Integrated soil quality index (IFI) was significantly positively related with soil quality index (SQI) (r=0.963**, n=29, p<0.001). The values of IFI and SQI shared the similar trends with re-vegetation and land use structure, both indexes followed the order of lunar slope (summit slope>backslope>footslope)>solar slope (summit slope>footslope>backslope)>abandon land (summit slope>backslope >footslope) in Yunwushan area with slope directions and positions, and followed the order of 20a>25a>15a>5a in re-vegetated grassland with different re-vegetation times. IFI and SQI presented the order of Pinus Tabulaeformis forest>Form. Robinia Pseudoacacia forest>bare land>grassland in Nanxiaohegou watershed, of Form. Robinia Pseudoacacia +Sophora viciifolia Hance mixed forest>Sophora viciifolia Hance forest>Caragana Korshinskii forest>Form. Robinia Pseudoacacia forest in Zhifanggou watershed, and of forest> unploughed abandon land>farmland>ploughed abandon land in Ziwuling area.(4) Classified soil quality of various re-vegetation areas in the Loess Plateau. Soil quality in grass land re-vegetated more than 15 years in Yunwushan, Pinus Tabulaeformis and Form. Robinia Pseudoacacia forest in Nanxiaohegou, Form. Robinia Pseudoacacia+Sophora viciifolia Hance mixed forest, Sophora viciifolia Hance forest and Quercus liaotungensis+Pinus Tabulaeformis mixed forest in Zhifanggou are in a high quality class, soil quality in abandon slope in Yunwushan, grass land and abandon land in Nanxiaohegou, Caragana Korshinskii and Form. Robinia Pseudoacacia forest in Zhifanggou, unploughed abandon land and farmland in Ziwuling are in a middle quality class; while soil quality in 5a grass land in Yunwushan, ploughed abandon land in Ziwuling, Caragana Korshinskii forest in Shanghuang and Liudaogou are in a low quality class that need further improving.(5) Revealed the periodical regularity of soil quality changes and found the optimal re-vegetation time. The improvement of soil quality can be classified into three stages in 25 years, that is, early reducing stage (0-15a), middle increasing stage (15-20a), and later reducing stage (20-25a). The improvement index of soil quality attained maximum after 20 years're-vegetation, suggesting the 20 year is the optimal re-vegetation time on the aspect of soil quality. The improvement of soil quality would delay about 15 years.(6) Found that the maintaining and adjusting of soil quality is of practical. The results of field investigation and laboratory analysis showed that planting grass and fencing are preferred to other measures in Shanghuang hilly area, Sophora viciifolia Hance forest is preferred in Zhifanggou watershed to Caragana Korshinskii forest. Besides, change in land use structure is suggested to guarantee the sustainability of land resources and soil quality. The results from this study further indicate that re-vegetation in the Loess Plateau should be conducted not only according to areas and vegetations, but also to lands and soils.