Modifying sandy soils with the fine residue from bauxite refining to retain phosphorus and increase plant yield

Production of alumina from bauxite in Western Australia results in large quantities of processing residue. The fine portion of the residue (red mud) has a high phosphorus (P) absorption capacity compared with the native sandy soils of the coastal plain. When neutralised with gypsum or acidic materials, the residue can be incorporated into, or spread on, the surface of sandy soils for horticulture using simple agricultural equipment. Neutralisation with gypsum is unnecessary for application to pasture at less than 100 t ha^–1. Field and laboratory experiments show that 10-80 t ha^–1 of bauxite residue, spread evenly over the surface of the soil, significantly reduced P leaching from coastal plain sands fertilized with superphosphate. Rates of 500 t ha^–1, or more, significantly increased the yield of pastures on well drained sandy soils, primarily due to the increased water holding capacity of the amended soils, while rates of 10-80 t ha^–1 significantly increased the yield of pastures primarily due to increased pH.Analysis of leachate from bauxite residue indicates that it is unlikely to cause adverse environmental impacts as a result of agricultural-scale amendment of sandy soils. Amendment with bauxite residue offers potential as a practical component of an integrated strategy to reduce P losses from sandy soils. Economic and logistic considerations indicate soil amendment may be most applicable to intensive land uses such as horticulture and for land treatment of wastewaters from animal industries and urban areas. However, economical methods are being developed to spread low rates of bauxite residue on land used for more extensive agriculture.