Sequential fractionation and characterisation (31P-NMR) of phosphorus-amended soils in Banksia integrifolia (L.f.) woodland and adjacent pasture

Fractionation and characterisation of soil P by sequential extraction or by 31P-NMR spectroscopy were used to assess a variety of soil characteristics, including the availability of P to plants, the transformations of native and added phosphorus and the effects of plant growth on pools and distributions of P. We used a modification of the technique of Hedley et al. (1982) and Tiessen et al. (1984) [Hedley, M.J., Stewart, J.W.B. and Chauhan, B.S., 1982. Changes in inorganic and organic soil P fraction induced by cultivation practices and by laboratory incubations. Soil Science Society of America Journal, 46, 970–976 and Tiessen, H., Stewart, J.W.B., Cole, C.V., 1984. Pathways of P transformations in soils of differing pedogenesis. Soil Science Society of America Journal, 48, 854–858] to assess the stability and transformations of sources of P (rock phosphate, Fe-phytate, RNA) added to soil under a stand of Banksia integrifolia and under an adjacent pasture. Pasture soils contained more P than soils under Banksia, but the distribution of P among fractions was similar for both soils. The different sources of P added to soils were recovered in largely discrete fractions. Most of the P in RNA added to Banksia soil was mineralized and leached, as PO43−, within 2 months, whereas additions of Fe-phytate and rock phosphate produced little PO43−. In the pasture soil, RNA was mineralized at a slower rate, but root growth (and presumably uptake of P) was rapid and less P was leached. Generally, the amount of P extracted using Chelex 20 cation-exchange resin was less than one third of that extracted using our modification of the methods of Hedley et al.(1982) and Tiessen et al. (1984). Results from 31P-NMR spectroscopy showed that most (>∼90%) of the P compounds extracted by the resin in all treatments were monoesters.