Effects of land-use patterns on soil aggregate stability and organic carbon in rocky desertification areas

The Salaxi town of Bijie City, Guizhou Province is a representative karst mountainous demonstration district, where the karst accounts for 74.25% of the entire area. The exposed rocks are dominated by limestone, limestone and sand shale, with widespread potential and mild rocky desertification. This region hosts zonal yellow soil, dominated by arable and forest land, with a small amount of grassland. These lands are used in six types， secondary forest, artificial forest, natural shrub grassland, artificial grassland, forest and grass interplanting land and sloping farmland, which have largely same slope angle, slop facing direction and elevation. By monitoring the number of soil aggregate, soil aggregate stability, soil aggregate organic carbon and other indices, this work analyzes the influence of the conversion of slope farmland into forest land, grassland and forest-grass interplanting land on the stability of surface soil structure and the content of organic carbon under different land use patterns, and reveals the stability of soil structure and carbon sequestration capacity after implementing rocky desertification control measures in this area, providing a scientific basis for the prevention and control of soil erosion and the improvement of soil erosion resistance in rocky desertification areas. The results show that， (1) the aggregate content of >0.25 mm increased significantly after the implementation of forestation and planting, with more plantation and secondary forests and less sloping farmland.(2) After the dry and wet sieve treatment, the stability of aggregates and erosion resistance characterized by GMD, MWD and D indexes and >0.25 mm aggregate content show that the soil aggregate stability of plantation and secondary forests was strong, whereas the soil aggregate stability of sloping farmland and forest-grass interplanting land was weak . (3) In general, the content of soil organic carbon of small-grained aggregate is the highest for different land use patterns, and the contribution rate of water stable aggregate organic carbon of >5 mm and 2-5 mm to soil organic carbon is the largest (except for sloping farmland). Large soil aggregates play a major role in the sequestration of soil organic carbon. After the transformation of sloping farmland into forest and grass land in rocky desertification areas, the number of large soil aggregates (>0.25 mm) increases, the stability of soil aggregates is enhanced, and the organic carbon content of soil aggregates does not exhibit significant increase. On the whole, returning farmland to forest and planting grass in rocky desertification sloping land is beneficial to the promotion of the stability of soil surface soil structure and the accumulation of organic carbon.