Mark Tibbett

The jarrah forest is a natural ecosystem with significant endemism in the flora and fauna. The forest stands on the western edge of the ancient Great Plateau of Western Australia on the granitic shield of the Yilgarn craton (2.5 Gya). The long-term migration of soluble iron and aluminium led to the formation of bauxite ore. The regolith ore is bound by surficial topsoil and deep pallid zone kaolinite clays, primarily used in land rehabilitation. We investigated the chemical fertility of the substrates, along with key physical properties. We found the capacity of these soils to provide a stable growth medium differed considerably in their ability to retain and supply nutrients. These substrates are deficient in nitrogen, phosphorus, and micronutrients. In the topsoil, 15% of total P is plant-available, while in the pallid zone layer, only 1% of total P is available. 31P-NMR showed no organic P in the pallid zone, whereas the topsoil had significant organic P and, consequently, a supply of phosphate ions. This shows the importance of organic P in the topsoil for ecosystem nutrition when inorganic fertilisers are not applied in state-of-the-art restoration schemes.