Effect of soil amendment with bauxite Bayer process residue (red mud) on the availability of phosphorus in very sandy soils

K. Snars, Robert Gilkes, J. Hughes

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

The chemical properties of red mud, a by-product of Bayer process refining of bauxite to alumina, make disposal of the material problematic. It is very alkaline (pH > 11), contains a large amount of sesquioxides, and thus has a very high P retention capacity. These characteristics have encouraged its use as a soil amendment to enhance P retention of soils so as to reduce leaching of P. To investigate the effect of added red mud on the availability of existing P in sandy soils an incubation experiment was conducted using 3 types of red mud (untreated red mud, red mud amended with 5% gypsum, and red mud leached with dilute acid to remove all soluble salts) mixed with 12 podsol topsoils at rates of 0, 2.5, 5, 10, 20, and 40 t/ha. The mixtures were incubated wet for 28 days in the dark at 20degreesC, both with and without a microbial inhibitor. The decrease in 0.5 M sodium bicarbonate extractable phosphorus (bic-P) was 40-60% of initial bic-P at 40 t/ha of all 3 red muds after wet incubation without microbial suppressant. This decreased to 20-40% after drying or with addition of the microbial suppressant. The decrease in bic-P was not due to the increase in pH due to red mud application and appears to involve both chemical and microbial actions. The increase in soil pH of up to 3 units would be beneficial for pasture production at most rates of red mud application and the associated increase in electrical conductivity is not sufficient to affect plant growth.
Original languageEnglish
Pages (from-to)1229-1241
JournalAustralian Journal of Soil Research
Volume41
Issue number6
DOIs
Publication statusPublished - 2003

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