Characteristics of soil calcium forms of rocky desertification areas in the Mengzi fault-depression basin, Yunnan

Calcium(Ca) is one of the main elements in the karst soil environment. Soil Ca is not only a base ion,which can affect the pH value of soil and the stability of organic carbon, but also has an important impact on the physical stability and water retention performance of soil; thus it is an important indicator of soil quality.The Mongzi fault-depression basin in the eastern Yunnan is one of the most serious rocky desertification areas of our country.It is of great significance to the rocky desertification control and ecological restoration to study the soil Ca forms distribution.This work focused on the soil in different landscapes of the rocky desertification area of the Mongzi basin (basin,slope and plateau). The improved BCR continuous extraction method was used to study the soil Ca forms and influencing factors in the basin.Results show that， (1) In the study area,the soil content of exchangeable Ca is the highest with large bioavailability.The order of all forms of Ca is exchangeable Ca (61.04%)>residual Ca (18.53%)>acid soluble Ca (17.44%)>water soluble Ca (1.63%)> organic bound Ca(1.36%).(2)The degree of rocky desertification has great impact on the morphological distribution of Ca. The higher the degree of rocky desertification,the higher the content of activated Ca, especially exchangeable Ca,which is mainly affected by the "aggregation effect" of exposed rocks.(3)The soil properties of organic carbon and total nitrogen content have significant influence on the Ca form, indicating that the Ca fixation and carbon fixation of lime soil in karst areas are processes of interaction and mutual influence.Therefore,in the process of rocky desertification control in the Mengzi basin,the influence of geological environment should be considered together with the climate factors,and species should be selected properly according to local conditions.All of these measures are of great significances to promote ecological restoration in rocky desertification areas.