The influence of centrifuging on phosphorus (Olsen P) soil test values

Abstract

Variation in soil Olsen P tests can arise from the method of separation of the solution extract from the soil. With increasing centrifugation of the NaHC03 extract solution, we observed a decline in solution P values and these approached the P values obtained on soil-filtered extracts. The decline in solution P with increasing centrifugation was associated with a decline in organic carbon in the NaHC03 solution. We caution against unpublished modifications to methods and recommend that for consistency, simplicity, speed and cheapness, the NaHCO3 extract be soil-filtered as in the original method.