Limestone soil in karst areas is the product of weathering and carbonate rock dissolution in tropical and subtropical regions. Limestone soil in karst regions has a Ca-rich alkaline geochemical environment, but the characteristics of calcium speciation in limestone soil remain unclear. Here, to study changes in calcium speciation in soil across seasons in a karst area, different geomorphological positions and soil samples were collected from the Yaji karst experimental site. Using European Community Bureau of Reference （BCR） methods, we analyzed and discuss soil calcium speciation and seasonal migration characteristics. We found that total soil Ca content was 2.80-11.75 g kg^-1, with an average of 5.25±0.68 g kg^-1 （mean±SE）. The order of content of each Ca speciation is extractable-Ca〉reducible-Ca〉residual-Ca〉oxidizable-Ca. In addition to oxidizable-Ca, other Ca species had a positive correlation with total calcium. The calcium content and various forms of calcium content decreased gradually with changing season, but in addition to differences in residual calcium across seasons, total calcium and other forms of calcium across seasons were not different. Total calcium and different forms of calcium content were highest at sloped areas; slopes and other landforms were different but differences between plain, saddle and depression areas were not significant.
