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 (Al 2 O 3 ) 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 (Fe 2 O 3 )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 Al 2 O 3 (%), r 2 = 0.45.(2) PBC = -0.004 + 1.532 organic C (%) + 22.26 Al 2 O 3 (%), r 2 = 0.57.(3) PA = 3.52 + 248.75 Al 2 O 3 (%), r 2 = 0.59.

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A glasshouse experiment was conducted to estimate the extent of leaching of molybdenum on acidic sandy soils from Western Australia. Sodium molybdate, at a rate equivalent to 40 g of molybdenum per hectare, was added to pots of soil either before or after leaching a column of the soil with the equivalent of 500 mm water. Molybdenum concentrations were determined in the leachate and in the wheat plants grown on the soils in pots after leaching. Approximately 10% of added molybdenum was removed with leaching from two grey sands, while negligible quantities were removed from three more acidic sandy soils. Leaching does not appear to be an important factor in the occurrence and recurrence of molybdenum deficiency on the yellow-brown acidic sandplain soils of the Western Australian wheatbelt.

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