| Other Abstract | The Karst Rocky Desertification was the biggest ecological environment problem in Guizhou Province and even the entire southwest, and it created the enormous barrier to the local economical development and the human survival. It has been attached more and more importance in recent years, but the austere facts were the overtaking of ecology construction and the lagging of basic researches. In the process of Rocky Desertification the change of soil quality, the anthropogenic disturbing ways, and the connected degeneration of the soil—vegetation system are the extremely important basic theory in the rocky desertification research. It can be used as the reference for Classification of rocky desertification, and it is also the important basic theory which is used to controlling the rocky desertification process and restoring the ecology environment.
This paper made quantitative analysis of the roles of soil and vegetation degradation in the process of rocky desertification, in order to find the evolvement rule of the soil quality, and the influence of the anthropogenic disturbing ways, then discussed the degenerated characteristic of soil—vegetation system and the covariant relations, analyzed the changes of soil quality by the basin internal factor such as slope position, and used the soil degeneration index to carry on the appraisal to it. The following conclusions were drawn from the analysis:
(1) The soil in the studied area were featured as following: shallow, profile level was not obvious, neutrality to slightly alkalescency. CEC and BS% values was high, and OM and total N was also rich. C/N was low, but N supply potential was high, the soil nutritive elements were rich, but P, K and Na content were relative insufficiency.
(2) In the process of rocky desertification, the density of soil increased, so the porosity reduced. The big water-stable aggregate reduced, then the small aggregate relatively increased; OM drained, and the total N content reduced. Some nutritive elements which is easy to move in the soil reduced in the process of rocky desertification, such as P, K, Na, Ca, Mg and so on, and the element which is difficult to move displayed increasing, such as Fe, Mn, Cu and so on. Its pH and CEC values also showed a declining trend. The soil nutrient availability reduced, each effective state of element content dropped, only effective Mn was exceptive.
(3) The most soil profile was A-D or A-C, but there are a few has been apparent heart soil. The A layer of soil have been relative good nutrition condition. In the process of rocky desertification, the clay content increased, particularly gathered on the bottom of soil more obviously. The geochemistry character relatively active elements content reduced, the outflow quantity in the soil upper formation was larger than the bottom, but the stable element accumulation quantity on the bottom was larger than the upper formation. CEC value was lower on the surface of the soil and higher on the bottom. Only the effective Mn, Fe content increased in soil, and the other elements reduced.
(4) In the process of rocky desertification, the physical and chemical properties of soil deterioration and degradation of vegetation reinforced each other, and forming a kind of mutual feedback of a vicious cycle. With the deepening Desertification, the vegetation succession was arbor → shrub → grass → sparse grass, its characterized mainly is as follows: low vegetation cover, the community structure was simple, N, Ca, Mg was rich, P, K, Na was deficient. By comparing and correlation analysis, plant growth reached the main limiting factor for P, K, Na, Mn, Zn.
(5) After a certain period of rocky desertification development, relatively flat topography of the region was easy to become yellow lime soil, its physical and chemical properties were between yellow and lime soil, the law of changing nature of the soil was even more obvious with rocky desertification development; the steep and rugged terrain of the region soil was easy to remain in the negative terrain, then formed the young black calcareous soil. Its physical and chemical properties were better, profile level were not more obvious than the yellow lime soil. So it should be distinguished in rocky desertification grading and comprehensive management
(6) We have already selected soil degradation evaluation index and given it weight, including the average thick of soil, OM, total N, pH, CEC, density, particle composition, water-stable aggregates, total P, Na, Ca, Mg, and Cu, alkali solution of nitrogen, effective potassium, iron, copper and zinc. Evaluation results showed that soil degradation and rocky desertification were synchronous development. The chemical nature of the degradation was even more obvious than the physical properties. It showed the relative strength of the physical nature degradation only on rocky desertification initially. Mild to moderate was the most sensitive stage of soil degradation, and degradation was the most strong, so it should be focused on prevention.
(7) Different human disturbance on soil quality was different. The deteriorating soil caused by and grazing was more stick, and its bulk density, density was larger than cutting soil. Degradation evaluation index indicated that the soil degradation under the influence of cultivation and grazing have been the most serious. The main reason was that the nutrient of the cultivation and Grazing soil depleted, then the changing of the chemical properties caused strong deterioration of soil quality. According to improving the chemical properties of the soil, the deterioration of cutting and burning soil would be slow down, thus soil quality was relatively good.
(8) Although the study may exclude various external factors, it was impossible to exclude the impact in the basin, such as slope position, slope aspect, slope shape and so on. The results showed that the slope position was an important impact factor for soil density, volumetric water content, gas rate, water-stable aggregates, C/N, total content of each elements and the content of its effective state. The soil degradation index indicated that soil degradation degree was uphill > the middle of the hill > downhill. |
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