Bauxite residue sand has the capacity to rapidly decrease availability of added manganese

Bauxite residue sand, even though a poor substrate for plant growth because of very high pH, salinity and sodicity, is required to be revegetated. Manganese deficiency is observed in residue-grown plants because broadcast applications of manganese fertiliser to the surface of residue deposits have a low residual value. In a laboratory experiment, manganese (as MnSO4) was added to fresh and 4-year-old residue sand and a sequential fractionation procedure performed at 0, 1, 4, 8 and 24 h and 6, 14, 21, 43, 73, 103 and 130 d. Extraction with DTPA estimated plant-available Mn, while sequential fractionation with various extractants yielded the following fractions: readily soluble [Ca(NO3)(2)]; weakly adsorbed [CaDTPA-B4O7]; carbonate-bound [HNO3]; and oxide-bound [NH2OH . HCl]. Residual Mn was calculated as a difference between the sum of all these forms and total Mn in residue sand. Transformation of manganese from the initially dominant readily soluble form to the less-available forms was very rapid (< 24 h). A change to fertilisation strategies is required if better efficiency of manganese application and uptake is to be achieved for plants growing on bauxite residue.