Characterization of basaltic clay soils (vertisols) from the Oxford land system in central Queensland

Abstract

Morphological, chemical and physical properties of basaltic clay soils (Vertisols-Usterts and Torrerts) from the Oxford Land System in central Queensland are described and compared over their geographical range of occurrence and also their position in the landscape. These soils are derived from undifferentiated basic lavas and interbedded pyroclastics of Tertiary age. Black earths are the dominant soil group. Position on slope had the biggest influence on depth of soil, with crest and mid-upper slope positions having more shallow (<0.9 m) soils than mid-lower and footslope positions. Soils have very high CEC and clay contents throughout the profile, are mildly alkaline at the surface and strongly so at depth, are non-saline and non-sodic (except in some footslope positions), and have an exchange complex dominated by calcium and magnesium. In the surface 0.1 m, extractable P and Zn, and total N and S levels are low and crop responses to fertilizer are probable. In comparison of 26 paired sites, where areas of native pasture and cultivation occur in close proximity, cultivated soils have lower organic C and total N, P, K and S levels than native pasture soils. This reflects a general decline in soil fertility under cultivation, and has implications for soil management and long-term soil stability.