Direct application phosphate rocks: Do soil phosphorus tests take site influence into account?

Conventional soil phosphorus (P) tests have been found unreliable where direct application phosphate rock (PR) is used. However, the iron oxide-impregnated filter paper (Pi) and mixed anion/cation ion-exchange membrane tests have been suggested as being suitable in this situation. These tests measure a part of the residual PR that contributes to the soil P status. However, the agronomic effectiveness of a PR depends on its rate of dissolution at a site. A soil test measuring residual PR in soil will be ineffective if the PR does not dissolve in the field. The dissolution rate is influenced by site properties such as drainage and rainfall as well as soil and PR properties. Soil samples from New Zealand pastoral sites where the PR dissolution rate was either very low or very high were used to investigate the influence of site and soil properties on the amount of PR-P measured by the tests. There was no significant difference in the amount of PR measured by either test between soils from the low and high dis...