Comparibility of results obtained by the use of different selective extraction schemes for the determination of element forms in soils

Two selective extraction schemes, that commonly known as Tessier's and that used by the Geological Survey of Canada (GSC), are compared. The nominal p hases identified include: adsorbed/exchangeable/carbonate, 'AEC'; amorphous Fe oxyhydroxides (including Mn oxides), 'amFeox'; organics and sulphides, 'org/sul'; and residual (silicates and more resistant minerals). Three stan dard reference soil samples, SRMs 2709, 2710 and 2711, were analysed in tri plicate for the elements Ca, Cd, Cu, Fe, Mn, Ni, P, Pb, Ti, V and Zn. Resul ts by both methods agree extremely well for Ca, Mn and Cd, and for Ni and V in SRMs 2709 and 2711. For other elements, there is a strong tendency for a higher percentage to be dissolved earlier in the GSC scheme (in the AEC, amFeox and org/sul phases). Consistently more Fe reports to the amFeox and org/sul phases by the GSC method, otherwise present in the residual phase b y the Tessier scheme. Results for P do not compare well, with a much greate r proportion of the element being extracted in the amFeox phase by the GSC procedure. Very little P appears to be labile by the Tessier protocol. This paper suggests that more research is needed into the nature of phases purp ortedly extracted by selective leaches.