Temporal-spatial Variability Of Soil Quality Under Different Vegetation Covering On The Loess Plateau

Soil properties have strong temporal-spatial variability, which is strongly affected by human activities. Planted tree-grass is a very important and effective measure of rebuilding ecological environment, and this process is controlled by soil texture, climatic and environmental conditions, vegetation types and its biology characteristic. So it is necessary to combine these factors for the vegetation rebuild project. Therefor, the purpose of this study was to reveal the temporal-spatial variability of soil physical properties, chemical properties and enzyme activity under different vegetation coverings, such as Robinia Pseudoacia, Caragana korshinskii and so on. It is of some theoretical and practical value for ecosystem rebuilding on the Loess Plateau.Based on the investigation of the total rebuilt vegetation level on the Loess Plateau, the study was conducted at Zhifanggou watershed. Soil samples were collected under different vegetation types (i.e. Robinia Pseudoacia, Caragana korshinskii) with different growth years, and under the different vegetations in the same growth years. The results are as follows:1. Temporal dynamics of soil properties as affected by vegetation (i.e. Robinia Pseudoacia and Caragana korshinskii)Different indicators showed different trends in Robinia Pseudoacia and Caragana korshinskii vegetation restoration. With respect to soil physical properties, bulk density of Caragana korshinskii soil reduced gradually, and there was no obvious trend about moisture; bulk density and moisture of Robinia Pseudoacia soil decreased then increased. As to soil nutrient, soil organic matter, total nitrogen, available nitrogen, available phosphor and available kalium increased with the growth of Robinia Pseudoacia and Caragana korshinskii, while soil PH reduced. Total phosphor increased in the Robinia Pseudoacia, while Caragana korshinskii showed opposite trend . About the soil enzyme, soil enzyme activity increased with the growth of Robinia Pseudoacia and Caragana korshinskii. Enzyme activity of Caragana korshinskii soil is higher than that of Robinia Pseudoacia's expect invertase. By correction analysis, it is the soil unease activity and invertase activity that can index the affect of Robinia Pseudoacia to soil quality. Soil unease activity is better than invertase activity; to Caragana korshinskii soil, it can be indexed by alkaline phosphatase activity, invertase activity and hydrogen peroxidase activity, and alkaline phosphatase activity is great.2. Spatial variation of soil properties along sloping land under different plantationsSandy, silt, coarse sandy and soil bulk density varieties in the way of wave under the different vegetation with the sloping length, and moisture varieties strongly in the way of wave. Among Robinia Pseudoacia soil, Caragana korshinskii soil and sloping farmland, organic matter, total nitrogen (TN) , total-P and all kinds of available nutrients concentrations were the highest in Robinia Pseudoacia, while, pH is the lowest. TP and pH is lower in the Caragana korshinskii soil than sloping farmland. Other nutrients concentrations were higher than the sloping farmland. Soil unease, alkaline phosphatase, invertase and hydrogen peroxidase activity are the strongest in Robinia Pseudoacia. All kinds of soil enzymes activity of Robinia Pseudoacia soil are 2.6, 1.6, 1.1 and 2.5times of Caragana korshinskii soil, is 6.1, 6.4, 1.3 and 37times of sloping farmland. The order of soil enzyme activity is Robinia Pseudoacia>Caragana korshinskii>sloping farmland. In the base of Nielsen's standard, under the sloping scope, TP is light change, and the other's nutrients are middle change. To the change of the soil enzyme activity, hydrogen peroxidase activity is light in all kinds of vegetation. Invertase is strong, and the others are middle.3. Soil quality changes as affected by different plantationThere were different affects of different vegetations on soil physical properties. Willow's function has significant impact on soil bulk density. Sabina can accelerate the content of the clay and the silt, and improve soil moisture, at the same time. Nitrogen concentration of Sabina soil is very high. There is very little difference of total phosphor concentration among all kinds of vegetation soils. The activity of the same enzyme is different in the different vegetation. The order of soil unease activity is Willowï¹¥Sabinaï¹¥Artemisia sacrorumï¹¥Caragana korshinskiiï¹¥Populusï¹¥comparison, hydrogen peroxidase is Populusï¹¥Caragana korshinskiiï¹¥Willowï¹¥Sabinaï¹¥Artemisia sacrorumï¹¥comparison, alkaline phosphatase is Willowï¹¥Sabinaï¹¥Caragana korshinskiiï¹¥Populusï¹¥Artemisia sacrorumï¹¥comparison, invertase is Sabinaï¹¥Willowï¹¥Caragana korshinskiiï¹¥Populusï¹¥Artemisia sacrorumï¹¥comparison.