Comparative study of phosphorus and potassium levels of basaltic soils associated with scrub and forest communities on the Darling Downs

Abstract

Morphologically similar scrub and forest basalt soils were investigated for differences in soil phosphorus and potassium levels. Surface samples (0-10 cm) from 181 scrub and 111 forest sites were analysed for five soil tests: 0.05 M H2SO4-extractable phosphorus, 0.5 M NaHCO3- extractable phosphorus, 0.05 M HCl-extractable potassium, total phosphorus and total potassium by X-ray fluorescence. Highly significant differences (P <0.001) between scrub and forest soils were found for each soil test when all sites were assessed in terms of regional differences based on vegetation. These differences were then investigated further for each of the three common Great Soil Groups - black earths, euchrozems and lithosols - and then for six individual soil series common to both the scrub and forest areas. An unexplained geographic trend in phosphorus values previously reported (1972) in the same area could be accounted for by this difference between scrub and forest soils. Similar differences in soil phosphorus and potassium for scrub and forest soils on other parent materials are also discussed. It was clearly shown that the scrub means were always greater than the forest means for all five soil tests for all soils combined, each Great Soil Group and each soil series, and that there is a strong association between vegetation distribution and these soil differences.