A rapid fractionation method for assessing key soil phosphorus parameters in agroecosystems

A wide variety of soil phosphorus (P) fractionation schemes have been developed and used extensively for over 60 years, however, most are laborious and provide limited information on key parameters such as P mobility and adsorption. We propose an alternative multi-stage extraction technique that it is possible to complete in one day. This involves separate analysis of three subsamples, including assessment of inorganic P (Pi) adsorption capacity, P fractions (sequential extraction with 1 M CaCl₂, Mehlich-3, 0.5 M NaOH, 1 M HCl, and total P (H₂SO₄-H₂O₂ digestion)). This provides data on potentially mobile Pi, plant-available Pi, moderately plant-available Pi, organic P, occluded P, the degree of P saturation, together with a “legacy P index”. Assessment of these parameters involved comparing two contrasting soils that had received similar P inputs as pig manure over two years. Results showed that P inputs significantly increased all soil P fractions, with concomitant significant increases in P saturation and legacy P. The findings of this study demonstrated the potential value in using the proposed methodology to provide a comprehensive suite of physico-chemical soil P data. This information may facilitate investigation and quantification of the impacts of land management and inputs on the dynamics and bioavailability of soil P in agroecosystems, although further assessment and validation is required