Phosphorus extractability of heavily fertilized soils from Norway

Increased incidence of soils with a large available phosphorus (P) reserve has created a growing interest in better understanding the P supplying capa city of those soils. In this work, seven conventional and P-sink soil P tes t procedures (Olsen-Ol, Mehlich3-M3, Egner-Egn, dilute CaCl2, distilled wat er, anion exchange resin membrane-AEM. and iron oxide-coated paper strip-Pi ), commonly used to evaluate potentially plant-available P were compared on eight Norwegian soils with low to high extractable P content. The anion ex change resin was also used in a sequential extraction experiment in which r epeated extraction of a soil sample was evaluated as a method to investigat e the release of soil P. The cumulative P removed in the successive extract ions fitted a first-order rate equation well. with the asymptote representi ng the ultimate releasable P or in other words, the overall amount of poten tially desorbable P. Distilled water and the P-sink soil P test methods res ulted the most accurate procedures in predicting the ultimate amount of des orbable P from the soils (r=0.961 to 0.989; p <0.001).