PHOSPHORUS ADSORPTION BY A RANGE OF WESTERN-AUSTRALIAN SOILS RELATED TO SOIL PROPERTIES

The capacity of 36 Western Australian soils to adsorb phosphorus (P) was measured by three different methods: P retention index (PRI), P buffering. capacity (PBC), and P adsorption (PA). The P adsorption values measured by all three methods varied markedly with soil type. When the P adsorption values were correlated with several soil properties, using simple and multiple linear regressions, PRI, PBC, or PA values were found to be significantly correlated with the aluminium oxide content of the soils. In addition, PBC and PRI was correlated with organic carbon content. The role of aluminium oxide (Al2O3) in the soil was apparently more important in determining the P adsorption capacity of the soils than that of iron (Fe), even though the iron oxide (Fe2O3)content of all the soils studied was consistently higher than the aluminium oxide content. The relationship between P adsorption and the selected soil properties, as determined by multiple linear regression, explained 45-59% of the variation: (1) PRI = -10.87 + 9.94 organic C (%) + 160.02 Al2O3 (%), r2 = 0.45. (2) PBC = -0.004 + 1.532 organic C (%) + 22.26 Al2O3 (%), r2 = 0.57. (3) PA = 3.52 + 248.75 Al2O3 (%), r2 = 0.59.