Research On Soil Quality Degradation Control Of Rocky Desertification Area

Soil is the foundation of human survival and human development. As the result of the special climate conditions and fragile geological environment in Karst region, the soil formation rate is slow and lacking of soil layer and nutrients. On the other hand, the important components of conserving water and soil are keeping and improving the quality of soil. However, the losses of water and soil would become intense by the degradation of soil quality. Therefore, it is necessary to study the soil quality, which includes soil bulk, humus content, and soil water conservation ability, so as to improve the ability of soil and water conservation. As the sharp conflict of population, resources and environment in karst mountain area, Chongqing, soil erosion and vegetation degradation are increasing as the result of excessive development and utilization of land. Consequently, the soil and water system in this area is under the environment of land barren, water shortage and ecologically fragile. At the same time, the trend of rocky desertification is obvious in this area.The targets were to analyze regional soil quality changes, to evaluate land productivity, and to plan land use and ecological restoration in rocky desertification area. Nanping Town in Jinfo Mountain area was selected as the study area in this paper. Field sampled soils were measured in lab and analyzed with EXCEL technologies, SPSS statistics methods, and GIS software to evaluate the regional soil quality changes. Comprehensive land fertility was evaluated with Delphi method to choose evaluating indices, fuzzy mathematics method to construct membership functions, and analytic hierarchy process (AHP) to determine the weighting values. The comprehensive indices of land productivity was classified into four grades reasonably by the cumulative frequency curve method and mapped with ARCGIS9.3software. Some suggestions about control measures of soil degradation and sustainable development of land resource were put forward according to comprehensive land productivity and its subarea for regional ecological restoration.The main results and conclusions were summarized as follows.(1) The soil properties were analyzed for assessment of regional soil quality changes included organic matter, total nitrogen, effective phosphorus, rapidly-available potassium, slowly-available potassium, alkali soluble nitrogen, bulk density, and soil pH. The results indicated that the regional soil is partial acidic. The average of soil bulk density is1.12g·cm-3; organic matter content,17.32-26.66g/kg; total nitrogen,1.21-1.86g/kg; total phosphorus,0.68-1.48g/kg. Compared with other regional soils, the average index content is low. Spatial distribution of soil nutrients is different from each other in this area. Organic matter shows higher content in southern and northern area than middle area. Slowly potassium content is in most of northern and central less than the rest of the area. Total phosphorus content is in the eastern part of the northern above the rest. Available phosphorus, on the whole, is higher in central section and west than in the southeast in this area. Total nitrogen content in the south and northeast are higher than in the middle. The spatial distribution of Alkali solution nitrogen is similar to that of the total nitrogen. The exchangeable calcium content is higher in the middle than in other part of this area. According to the evaluated results, the soil nutrient content is generally low in the study area, and less than that of the national average.(2) According to comprehensive indices of land productivity, the areas of the first, second, third, fourth grade were12.75km2,76.41km2,114.88km2, and66.57km2respectively. They severally account for12.75%,28.23%,42.45%, and24.60%in total area. The land of the first and second classes most partially distributed in the northern plains, where the soil was deep, flat and has good water resource and irrigation and drainage facilities. The third class area is the largest, which widely distribute in the low-lying of the central region, north central topography drought and high mountains in southern. The third class area mainly distributes in the area with high topography, large slope, low nutrient content, acid soil and common phosphorus deficiency. The land of the fourth class mainly distributes in southeastern area where the altitude is high, climate is cold, and water is short. The nutrient content of the soil is relatively plumpish and the soil structure is not bad but the nutrient is hard to decomposed and unavailable because of the cold temperature of the soil and air. The growth time of crops become sluggish and long, and even fruits get immature. According to the special distribution characteristic of land productivity, its grades were closely related to physiognomy types, rocky desertification degree, and the altitude.(3) The land resource of the whole study area was divided into four areas including comprehensive cultivated land zone, the improved land zone by soil fertilization, the amendatory zone by environmental conditions, and zone by natural vegetation recovery according to the soil nutrient status and characteristics of natural environment. The comprehensive cultivated land zone, which needs improve comprehensively, should be improved by the economic investments and protected strictly. The secondary land zone, which needs to be improved by increasing soil fertilization, should be adjusted the application of proportion of nitrogen, phosphorus and potassium, cultivate green manure to increase the soil nutrient content rationally to cooperate with the realistic soil situation. It needs to take a proper mixture of organic fertilizer and fertilizer, to promote straw returned comprehensively and to forbid burning strictly. To improve soil properties and economic benefits of the area, farmers are suggested to choose some suitable and characteristic crop to plant and to establish a good intercrop measures. In the third zone, where need to improve land environmental conditions, the government should strengthen the construction of drainage and irrigation facilities, change sloping fields to terrace fields, and build the platform and fish-scale pits, etc for soil and water reservation. A forestation policy and soil and water conservation policy should be carried out facilitate for the serious rocky desertification area. In the fourth zone, it is necessary to restore vegetation by planting easy living low grass and shrubbery, or leaving weeds growing freely for little disturbance, ecological restoration, and water conservation.