Land use effect on soil aggregates in the karst hilly areas--A case study in Qianjiang, Chongqing, China

Soil structure deterioration is a general phenomenon due to soil degradation by caused erosion especially in karst areas. The paper chooses Qianjiang as a case study and analyses the composition, stability of soil aggregates and its influencing factor under 4 different land use types. The result shows that most of the soil particles in the study area are smaller than 0.05mm in diameter and the soil has a higher soil clay contents (greater than 0.001mm in diameter). The topsoil particles will become coarsing or sandy obviously when the soil is tilled. The discrepancy of dry aggregate contents in the soil is not apparent, but the composition and water-stable aggregates are quite different with each other under different land use types. The contents of water-stable aggregate (>1mm and >5mm in diameter) decreases from shrub-grass land to woodland, abandoned land and cultivated land, while the contents of water-stable aggregate which have a diameter of big than 0.25mm decreases from shrub-grass land to abandoned land, woodland and cultivated land gradually. Shrub-grass land is the highest in content of stable-soil aggregate that their stability is highest; and the cultivated land is the lowest. The water-stable aggregates are mainly controlled by organic content, therefore, increasing the organic content is the key to modify the soil structure in karst hilly area.