Bauxite residue from alumina refining was used to coat granules of single
superphosphate to reduce the leaching of phosphorus in coarse, sandy soils for
pastures in high rainfall areas of south-western Australia (>800 mm annual
average). The impact of coating the superphosphate on the leaching of
phosphorus was measured in a glasshouse experiment and the effectiveness of
the fertiliser using dry herbage yield of subterranean clover
(Trifolium subterraneum) was measured in a field
experiment. The glasshouse experiment measured the effect of coating the
superphosphate with bauxite residue at 0, 5, 10, 15, 20, 25, 30, 35, and
40% by weight. A coating of 25% (by weight) was chosen for the
field experiment.
In the glasshouse experiment, the coated granules were applied to columns of
soil, where subterranean clover was grown under leaching conditions. A coating
of 30%, by weight, reduced leaching of single superphosphate by about
half. Increasing the coating of bauxite residue also increased the phosphorus
uptake and increased the plant growth.
In the field trial, the effectiveness of single superphosphate with a bauxite
residue coating of 25% by weight was increased on average by
100% in Year 1, 303% in Year 2, and 158% in Year 3,
relative to freshly applied single superphosphate. The bauxite residue coating
also increased the phosphorus content of the herbage in a similar manner to
the increases in yield. Limited soil phosphorus tests showed only minor
increases in the residues of phosphorus where the superphosphate had been
coated with bauxite residue.
The Impact of Micelle Formation on Surfactant Adsorption–Desorption