Effects of calcium,iron and aluminum fractions on the phosphorus bioavailability in limestone soil of karst region

In this paper,the effective relationships between phosphorus (P)in the soil of the karst region and the fractions of calcium,iron and aluminum have been studied to provide theoretical basis for stabiliza-tion of karst bio-system and lime soil fertility.The fractions of mineral elements in limestone soil at different stages of development were detected by improved BCR sequence extraction method and the relationship be-tween total phosphorus and available phosphorus was analyzed.The results revealed that the concentration of total soil phosphorus and readily available phosphorus decreased with the development of limestone soil. The concentration of total P decreased to 76.7% and readily bioavailable P decreased to 84.7%.The positive corrections occurred between total and readily bioavailable P with the acid extractable,reducible and residual fractions of calcium,oxidable iron and aluminum,reducible aluminum.Total iron,aluminum and residual a-luminum had negative corrections with total and readily bioavailable P.The absolute correlation coefficients were higher than 0.9.With the development of limestone soil,the lack of total P and readily bioavailable P was more and more prominent for the limestone soil quality and fertility.