The Research On Spatial Variability And Comprehensive Evaluation About Soil Fertility Of Rockification Hill In Nanping Of Chongqing

Currently, the desertification problem has been restricted the development of ecological construction in western China which is an important scientific question not be avoided. The sustainable developments of social and economic has been seriously impacted in this area, particularly the southwest of China. Soil fertility is one of the most important ecological functions, especially in ecologically fragile areas, the spatial distribution of soil nutrients directly affect the level of soil productivity in the region and ecological restoration of the way and direction. Thus it is the key issues that exploring the relationship between soil nutrients and the environment process to rationally instruct the work such as soil&water conservation, ecological restoration and agricultural production in desertification areas. According to a survey, in karst areas because of the declining soil quality the land difficult to use was as much as 20% to 30%, and the rate is accelerating now. Early studies have shown that the soil degradation under a karst environment is an important part of karst rocky desertification,an important factors affecting the deterioration of ecological environment of karst areas and a key aspect of constraining sustainable agricultural development. Therefore, it is very necessary to carry on the research about spatial heterogeneity of soil nutrients and soil quality assessment in desertification areas, particularly the potential desertification areas.Studying with the karst rockification hill in Nanping of Chongqing as an example for case study,51 soil samples were collected by random distribution from the 0～20cm topsoil.Eight nutrient contents were selected and determinated including total nitrogen, total phosphorus, total potassium, available nitrogen, available phosphorus, available potassium, organic matter and pH value.Based on these soil experimental data, the method combined with geostatistics and geographic information systems (GIS) methods was used to discuss the spatial variability characters of soil nutrient elements in the Rocky Hill area. Simultaneously, selecting the above eight indicators of soil nutrients as the evaluation factors, the fuzzy comprehensive evaluation methods was used to evaluate the soil fertility and assess the quantitative of soil fertility. The main conclusions obtained are as follows: (1)The descriptive statistics of soil nutrients in the study area showed:available N content is high, but the total amount is low, lack of back-up reserves; available phosphorus, total phosphorus, available potassium and total potassium have higher coefficient of variation, their distribution in space are very uneven and belong to highly variable; organic matter not only has a low content, but has a greater variability; generally pH value of the whole region was neutral and Partial alkaline, and has the smallest coefficient of variation. The results of the evaluation for the eight indicators showed that:the overall level of soil fertility in typical area was lower,90% of the soil was in a moderate or leaning infertile level. The distribution of more fertile soil only limited to the slope foot region,while the soil fertility located on the hill slopes is low. Furthermore, with the increase of the elevation and the slope,the soil fertility decreased gradually and more barren.(2) Examining normal distribution of the soil nutrien. Soil total nitrogen, available nitrogen, organic matter and pH value presented close normal distribution. Total phosphorus, total potassium, available phosphorus and available potassium, presented logarithmic normal distribution. The result of semivariogram analysis on soil nutrient data displayed:the theoretic model of the soil total nitrogen, total phosphorus, total potassium, available phosphorus, available potassium, pH value were exponential;available nitrogen and organic matter were gussian. According to the grading criteria about the degree of regionalized variables in space-related, we could know that:total phosphorus, total potassium, available nitrogen, organic matter and pH value have strong spatial correlation; total nitrogen, available phosphorus, available potassium have medium spatial correlation.(3)According to the choice of semi-variance model, the graphs of soil nutrients interpolation were drawed by the Kriging optimal interpolation. The overall distribution of soil organic matter content is that lower in the north and gradually increase towards south and east. Total nitrogen and available nitrogen have almost same distribution characters with organic matter,but only in the local area there are some differences. The the overall distribution structure of soil total phosphorus and available phosphorus is not very clear, large spatial variability, distribution most broken, and most complex distribution pattern. The total potassium content was low, but the south-east were higher, occurred in the midwest and north-central slightly staggered high and low values, accompanied by a significant low area, breaking the continuous distribution of total K. The trend of available potassium shows from southwest to northeast was regularly ladder-like reduced, and the spatial distribution has clear direction and hierarchy compared with others, its scale of variation should be beyond the study areas. Soil pH values has the lowest coefficient of variation in all of the investigated fertility elements, and its spatial distribution pattern of the overall performance display obviously "sour island effect", namely:the soil in regional centre was acidic, and pH increases radially at different levels to the surrounding.