Effects Of Accelerated Erosion Caused By Deforstation On Soil Quality Degradation Process In The Ziwuling Area

Accelerated erosion process and soil degradation caused by deforestation is important research topic in soil erosion effect assessment. Using the inetrgrated research methods of fix position observation, field survey, field sampling collection, chemical analysis, and principal component analysis, this thesis had studied the process of soil degradation resulted from deforestation in the Ziwuling area by analyzing the deforestation's effects on soil quality from soil physical, soil chemical, soil enzyme activity and soil microbial quantity. Finally, we built evaluation index system by selecting sensitive indexes and provided some important scientific evidences for Loess Plateau degraded ecosystem's restoration and rehabilitation. The main results were summarized as follows:1) After forestland was destroyed into farmland, the main erosion type changed from sheet erosion to intensive rill and severe shallow gully erosion, accelerated soil erosion was severe and erosion intensity was hundreds to thousands times greater than those in the forestland prior to deforestation. With the increase of the deforested years, soil erodibility parameter increases. As slope length increased on hill-slope in a shallow gully catchment that has been destroyed for 15 years, soil erosion intensity tended to increase; soil erosion intensity in gully channels was greatly higher than those in gully slope.2) As years of deforestation increased, soil bulk density gradually increased while soil capillary porosity gradually decreased; the ratio of soil water stable aggregates went down gradually and the ratio of the small aggregates increased; the ratio of the 0.05～0.01 mm soil clay gradually increased while >0.25 mm soil clay decreased which show soil coarsening phenomenon is obvious. With years of deforestation increased, soil total N, organic C, fungi, alkaline phosphates activity and inverters activities decreased; at the beginning years of deforestation, the falling speed of soil total N, organic C, fungi, alkaline phosphates activity, inverters activities were higher then declined.3) Due to 15a of serve soil loss, 0-15cm topsoil nutrient and soil microbial quantity...