Evidence of accelerated soil acidification under Stylosanthes-dominated pastures

In temperate Australia, accelerated soil acidification through the introduction of legume-based pasture systems is a major limiting factor to their sustainability. In this study, soil samples were collected from paired sites (developed u. undeveloped) to a depth of 90 cm to assess acidification rates under Stylosanthes spp. based pasture production systems in the semi-arid tropics of central and northern Queensland and the Northern Territory, Australia. Net acidification rates varied from 0·2 to 10·6 kmol H+ /ha· year for the sites sampled. The highest rate of acidification was observed under an irrigated Stylosanthes seed production system. Since acidification was measured by difference between paired sites, the total acidification rate of the developed sites is likely to have been underestimated. The contribution from the export of meat products was estimated to be 0·022-0·035 kmol H+ /ha· year on those sites with suitable records. Acidification occurred to depth on all sites that exhibited accelerated acidification, which makes conventional remediation methods impractical in these extensive grazing systems. Pedotransfer functions to predict the pH buffering capacity of a soil were developed for surface, subsoil, and the entire profile based on soil organic carbon, clay, and silt content. Management strategies to minimise the negative impact of Stylosanthes pastures are suggested.