Characteristics of calcium fraction distribution in soil under different land use types in karst fault-depression basins

Limestone soil in karst regions is characterized by high pH and calcium (Ca) content, which is one of the key elements in determining the structure and function of karst ecosystems, and is significantly affected by land use types. However, so far there are few studies on soil Ca fraction distribution under different land use types in karst fault-depression basins. This study chose four land use types including grassland, plantation, cornfield and dragon fruit landing the Bisezhai village, Xibeile country in Mengzi City, Yunnan Province as objectives, all of which are characterized by typical karst landforms. The BCR three-step sequential extraction method was used to determine the content of different Ca forms under different land use types in karst areas and influence factors. The results show land use types significantly influence soil total Ca content and its fraction distribution. Total Ca and various Ca forms in grassland soil are greatly higher than other land use types, and the lowest values appear in cornfield. The exchangeable Ca form is dominant in all soils, accounting for 59.4%-74.8% of total Ca, while the content of bound to organic matter-Ca is the lowest, accounting for 0.5%-1.0% of total Ca. The contents of total Ca and various Ca forms are significantly positively correlated with organic carbon, total N, total Mg, CEC, and pH. These data indicate that total Ca and various Ca forms interact with the physical and chemical properties of the soil to some extent.