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 capacity of those soils. In this work, seven conventional and P-sink soil P test procedures (Olsen-Ol, Mehlich3-M3, Egner-Egn, dilute CaCl2, distilled water, 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 exchange resin was also used in a sequential extraction experiment in which repeated extraction of a soil sample was evaluated as a method to investigate the release of soil P. The cumulative P removed in the successive extractions fitted a first-order rate equation well, with the asymptote representing the ultimate releasable P, or in other words, the overall amount of potentially desorbable P. Distilled water and the P-sink soil P test methods resulted the most accurate procedures in predi...