A. D. Noble, M. Cannon and D. Muller

Abstract

In temperate Australia, accelerated soil acidification through theintroduction of legume-based pasture systems is a major limiting factor totheir sustainability. In this study, soil samples were collected from pairedsites (developed u. undeveloped) to a depth of 90 cm to assess acidificationrates underStylosanthes spp. based pasture productionsystems in the semi-arid tropics of central and northern Queensland and theNorthern Territory, Australia. Net acidification rates varied from 0·2to 10·6 kmol H⁺ /ha· year for thesites sampled. The highest rate of acidification was observed under anirrigatedStylosanthes seed production system. Sinceacidification was measured by difference between paired sites, the totalacidification rate of the developed sites is likely to have beenunderestimated. The contribution from the export of meat products wasestimated to be 0·022-0·035 kmol H⁺/ha· year on those sites with suitable records. Acidificationoccurred to depth on all sites that exhibited accelerated acidification, whichmakes conventional remediation methods impractical in these extensive grazingsystems. Pedotransfer functions to predict the pH buffering capacity of a soilwere developed for surface, subsoil, and the entire profile based on soilorganic carbon, clay, and silt content. Management strategies to minimise thenegative impact ofStylosanthes pastures are suggested.