The Incidence of low phosphorus soils in Australia

Background: Low phosphorus (P) soils have been described as a widespread characteristic of the Australian continent and associated with sclerophyll leaf traits. In that context we ask: what proportion of the continent is low-P and how much does this vary between regions? Methods: 9234 locations sampled for soil total P from the Australian National Site Soil Data Collation were analysed. In order to make some adjustment for uneven spatial sampling we area-weighted the data using subregions from the Interim Bioregionalisation of Australia. Results: Topsoil total P concentrations ≤100 mg kg⁻¹ were widespread, but not a majority of the continent (estimated 25 %). The western Monsoon Tropics (65 %), southwestern Australia (50 %), and southeast South Australia (38 %) were estimated to have larger fractions of the sampled landscape ≤100 mg kg⁻¹ than eastern Australia (13.5 %), but not a lower range of values. Total P values across the continent included a large fraction (33 %) in the range 101–250 mg kg⁻¹. Conclusions: Continent-wide soil P levels low enough to favour long leaf lifespans for nutrient conservation and a variety of sclerophyll traits were widespread. It is time to move away from the qualitative dichotomies between low- and high-P that have characterised discussion of Australian vegetation, to a more quantitative view.