Surface soil-pH map of Queensland

Abstract

Surface soil pH can influence biological activity, nutrition and various chemical processes in the soil. Low pH or acidity is causing major concern in southern Australia, prompting requests for details on the extent, severity and distribution of acidic soils in Queensland. By creating a soil pH database, using an appropriate base map, rainfall isohyets and GIS technology, a coloured pH map of surface soils was produced at a 1:5000000 scale for the entire State. As most samples were from virgin or little disturbed sites, the map generally reflects naturally occurring soil pH. Developed horticultural, agricultural and fertilized pastoral areas are likely to have lower pH than that mapped. About two thirds (63.1%) of Queensland's soils have acidic surfaces, 9.5% neutral and the remaining 26.9% are alkaline. The major proportion (74%) of the > 1200 mm rainfall zone is strongly acid, and the remainder is medium acid or acid. Much of the sugar growing areas occur in this zone. Surface soil pH generally decreases as rainfall increases and to a lesser extent from subtropical to tropical climate. In addition to climate, identification of the soil type assists with predicting pH, as the organic, coarse and medium textured soils and massive earths are more likely to be acid and have low buffering capacity. Depending on the land use, such soils may require regular liming or minimizing of net acidifying practices for long term sustainability.