Abstract:

Twenty-five pasture soils were sampled from high-rainfall zones of southeastern Australia to examine relationships between soil properties, and between soil properties and P buffering capacity (PBC) measures. Correlations between PBC values and soil properties were generally poor, with the exception of oxalate-extractable Al (Al_ox) (r ≥ 0.97). Predictions of PBC were further improved when clay, as well as Al_ox, was included in a linear regression model (r² ≥ 0.98). When Al_ox and oxalate-extractable Fe were excluded from the modelling exercise, a more complex three-term linear regression model, including pH_H2O, exchangeable H and cation exchange capacity, adequately fitted both PBC values of the 25 soils examined in this study (r² ≥ 0.76). However, the Al_ox, Al_ox plus clay and the three-term models gave poor predictions of the PBC values when the models were validated using 28 independent soils. These results emphasize the importance of model validation, because predictive models based on soil properties were not robust when tested across a broader range of soil types. In comparison, direct measures of PBC, such as single-point P sorption measures, are more practical and robust methods of estimating PBC for Australian soils.

Keywords: Phosphorus; sorption; buffering; soil properties; models; single-point phosphorus sorption; Australia

Document Type: Research article

DOI: 10.1111/j.1475-2743.2006.00042.x

Affiliations: 1: Tasmanian Institute of Agricultural Research, University of Tasmania, PO Box 3523, Burnie, Tas. 7320, Australia 2: Department of Primary Industries, RMB 2460, Ellinbank, Vic. 3821, Australia 3: Department of Agricultural Sciences, La Trobe University, Bundoora, Vic. 3086, Australia