Effects of different land use types on soil anti-erodibility in Chongqing karst depression and karst-hill peak areas

The karst area in southwest China is the largest one,which is mainly located in Yunnan Province, Guizhou Province and Sichuan Province. Beibei district of Chongqing belongs to subtropical monsoon humid climate,and is controlled by the brush fold of Huayin mountain.Its geological structure is the parallel ridge valley landform of "one hill three ridge two valley",which is composed of karst depression-hills in eastern Sichuan.The carbonate rocks are mainly Triassic Jialingjiang formation (T1j), Feixianguan formation (T1f) and the Permian Maokou formation (P2m). The developed soil is yellow and brown calcareous soil. Under the influence of geology and climate, the soil is seriously eroded by chemical dissolution, gravitational and fluvial erosion.In order to explore the changes and differences of soil anti-erodibility under different land use types,and provide scientific basis for soil erosion control and ecological reconstruction in karst area of Chongqing. The topsoils of 5 land use types,including cultivated land, abandoned land, shrub-grass slope land, forest land and orchard,were selected in depression-hill peak area of Jigong karst mountain in Chongqing.Through the combination of field survey and lab analysis,11 common closely indexes related soil anti-erodibility were screened and comprehensive evaluated using the principal component analysis method.The results show that: the soil in the study area belongs to clayey to loamy soil, and the most easily eroded particles ranged from 0.05 to 0.25 mm. The optimal indexes on behalf of soil anti-erodibility are >0.25 mm aggregate destruction rate, >0.25 mm water stable aggregate content, degree of aggregation, <0.01 mm physical clay content, structural particle index and <0.001 mm clay content. That is, the lower the aggregate destruction rate >0.25 mm, the higher the content of water stable aggregates content of >0.25 mm, the degree of aggregation, the physical clay content <0.01 mm, the structural particle index and the clay content of <0.001 mm, the stronger the anti-erodibility of karst soil. According to the synthetic index analysis, 3 principal components are extracted and the comprehensive evaluation model of soil anti-erodibility was established.The order of evaluation of soil anti-erodibility was， forest land > shrub-grass slope land >abandoned land> orchard> cultivated land. It is suggested that appropriate returning cultivated land to forest or grassland in the karst area will help to reduce water and soil loss, and reasonably human activities can improve soil anti-erodibility and capacity of water and soil conservation.