Method for the analysis of oxygen isotopic composition of soil phosphate fractions.

The isotopic signature of oxygen in phosphate (δ(18)O(P)) of various soil fractions may shed light on P transformations, including phosphorus (P) recycling by soil microorganisms, uptake by plants and P adsorption, precipitation and release by oxides and minerals, thus increasing our understanding on P cycling and lability in soils. We developed and tested a protocol to extract and purify inorganic phosphate (Pi) from different soil fractions distinguished by binding strength and precipitate it as silver phosphate (Ag(3)PO(4)) for δ(18)O(P) analysis. Soil P is extracted sequentially using water, NaHCO(3), NaOH and HCl and Pi in each solution is purified and precipitated as Ag(3)PO(4).