Comparison of Direct Extraction and AOAC Official Methods for Available P2O5 in Fertilizers: Collaborative Study

Abstract

Fifteen fertilizer samples were sent to 13 laboratories for determination of available P2O5. Eleven laboratories, including author's laboratory, completed the analyses. Each sample was analyzed twice for available P2O5 by the new direct extraction method, and by either of the AOAC Official Methods using direct or indirect extraction. Results were favorable for the new direct extraction method even though the range and types of samples were highly variable. The direct extraction method was adopted first action by AOAC INTERNATIONAL.