Can organic amendments be used to improve the properties of bauxite processing residue sand?

The effects of adding of a range of organic amendments (biosolids, spent mushroom compost, green waste compost and green waste-derived biochar), at two rates, on some key chemical, physical and microbial properties of bauxite processing sand were studied in a laboratory incubation study. Addition of all amendments tended to decrease bulk density and macroporosity but increase total porosity, available water holding capacity and water retention at field capacity (-10 kPa). Addition of biosolids, mushroom compost and green waste compost all increased soluble organic C, microbial biomass C and basal respiration. The germination index of watercress grown in the materials was greatly reduced by biosolids application and this was attributed to the combined effects of a high EC and large concentrations of extractable P and NO3 -N. We concluded that the increases in both water retention and microbial activity induced by additions of the composts is likely to improve the properties of residue sand as a growth medium during revegetation.