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).