Assessment of phosphorus bioavailability in cultivated Andisols from a long-term fertilization field experiment using chemical extractions and soil enzyme activities

Various chemical extraction methods have been used to evaluate soil phosphorus (P) availability in different ways, and therefore inconsistent results are often obtained. This study examined the usefulness of the resource allocation model for extracellular enzymes for evaluating P availability in soils from a more biological perspective. Potential P availability was evaluated using the Truog and Bray-2 tests, the Hedley sequential extraction procedure, and enzyme activity assessments in cultivated Andisols from a 70-year-old fertilization experiment. Both the ratio of acid phosphatase to beta-D-glucosidase activities and the ratio of alkaline phosphatase to beta-D-glucosidase activities showed significant negative correlations with potentially available inorganic P, suggesting that microorganisms preferentially expended resources in the form of phosphatase production rather than beta-D-glucosidase production to acquire P. Additionally, crop P content had a significant negative relationship to the ratio of alkaline phosphatase to beta-D-glucosidase activities. These results suggest that the resource allocation model for extracellular enzymes is useful for evaluating P availability in Andisols.