This study used field lysimeters to investigate the reduction in the leaching of phosphorus (P) applied as superphosphate fertilizer from a very sandy Swan Coastal Plain soil treated with bauxite processing residue (red mud) neutralized with either waste gypsum from the phosphate industry or ferrous sulfate (copperas) from the titanium dioxide industry. Addition of 500 t ha-' red mud/gypsum or 200 t hap1 red mud/copperas were found to reduce the leaching of P to below 3 kg ha-l for application rates of 270 and 80 kgP ha-1, respectively. Water retention from these excessively well drained soils was increased by 14 and 50% by the addition of 200 and 2000 t ha-l red mud, respectively. The pH of the leachate for all rates of red mud/copperas application increased from approximately 4 to range between 7 and 7-5. The concentrations of Na and SO4 were about 8 and 17 g1-l, respectively, in the initial leachates collected from the 2000 t ha-' red mud treatment but declined to approximately 0.4 and 2.0g l-1 after 3 years of leaching. The Ca leaching appeared to be initially controlled by the solubility of the excess CaSO4 remaining after red mud neutralization, with concentrations ranging between 0.3 and 0.5 g l-1 before declining to approximately the levels for untreated soils of 0.01-0.06g l-1. The Na, So4 and Ca concentrations in the leachates from the 500 t ha-l red mud/copperas treated soil decreased to acceptable levels after 2 years. High total soluble salt (TSS) levels associated with high levels of residue application may affect pasture production in the years immediately following soil amendment

This paper reports on the gamma (�) radiation flux from sandy soils of the Swan Coastal Plain treated with bauxite residue/gypsum at various application rates and assesses the radiological significance of soil amendment in relation to currently accepted standards. Amendment rates of up to 2000 t ha-1 of bauxite residue were used. There is a linear increase of incremental � dose with increasing rate of residue. The 1 mSv limit for incremental � dose exposure for the general public is reached for 100% occupancy at an amendment rate of 1500 t ha-1 of bauxite residue. The gamma rate of approximately 0.15 �Gy h-1 is similar to that for soils of much of the area between Bunbury and Capel in the south-west of Western Australia and is significantly lower than levels for Minninup beach where there are deposits of mineral sands.

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