Comparison of several non-biological methods for evaluating soil and fertilizer phosphorus availability from rock phosphate

In this paper the results of a one-year laboratory experiment on the availability of fertilizer-derived phosphorus are presented. Samples of 20 representative soils were incubated for 100 days with superphosphate and two 'soft' phosphate rocks. The soils were analyzed for available phosphorus content by 4 different non-iso-topic methods and by the isotopic exchange method. Rock phosphates were very poor sources of available phosphorus while recovery coefficient of P from triple superphosphate was almost 50%. The most suitable method for estimating fertilizer-derived phosphorus availability was the Egner-Riehm DL extraction E value calculated from isotopic exchange kinetics. This method corresponded closely to the amount determined from paper strip extracted phosphorus (Pi) and phosphorus exchanged on anion membranes. The paper-strip P and anion membrane P were both good methods for measuring the Cp value (P concentration in soil solution). (author)