Deep banding improves residual effectiveness of manganese fertiliser for bauxite residue revegetation

Revegetation of high-pH substrates such as bauxite residue sand (BRS) can be problematic, since poor availability of nutrients like manganese (Mn) requires extensive and frequent fertiliser additions to maintain plant productivity. Recent glasshouse studies have shown improved growth and Mn nutrition of deep-rooted, perennial lucerne ( Medicago sativa L.) growing in BRS when Mn was banded deep below the surface. Deep banding of Mn fertiliser shows promise in having long residual effectiveness in BRS. A field study involving deep-banded Mn in a BRS disposal area was undertaken. Manganese fertiliser, banded at a rate of 15 kg/ha approx. 0.18 m deep, provided effective supply of Mn to lucerne for at least 2.5 years, while 5 separate surface-broadcast applications ( 15 kg Mn/ha each) were required over the same period to maintain similar lucerne productivity. Shoot and root yields and Mn concentrations in shoots were consistently greater in the banded than broadcast treatments. Root extension deeper than 30 - 40 cm was largely inhibited by a physical compaction layer and an increase in pH with depth. Lucerne root length density was increased significantly by deep banding of Mn. In conclusion, deep banding of Mn fertiliser can improve sustainability of revegetated BRS areas and, potentially, productivity of other high pH substrates, by reducing the frequency and amounts of Mn fertiliser additions required for healthy plant growth.