An investigation of the base status of soils from the Lockyer Valley uplands, and some implications for land use

Abstract

Samples were examined from 129 profiles representing the major soils on all of the parent material types occurring in the Lockyer Valley Uplands. The base status and CEC were determined by an unbuffered silver thiourea method and pH, and conductivity of the 1:5 soil/water suspensions measured. A factor analysis of the data showed that 62.5% of the variation could be accounted for by three factors, each of which described a different facet of soil development. Factor 1 was related to the balance between Ca and Na+Mg. Factor 2 was mainly concerned with salinity, pH and cation saturation, whereas factor 3 was related to the balance between Ca and exchangeable Al. The soils were classified into seven groups according to the factor 1 scores for the Al horizon, and the factor 2 and 3 scores for the B horizon. Parent material and Great Soil Group classification proved only to be a general guide to base status. Nearly all the soils had Ca-dominant surface soils with low base saturation and salinity. They became more Na + Mg dominant, and more saline, with increasing depth, and many of the podzolic soils had acid B horizons with high exchangeable Al. The best agricultural soils are the yellow-brown earthy soils, and sands developed on Ma Ma Creek Sandstones, and these tend to be Ca dominant and non-saline at least in the upper solum. Of the clay soils, although most possessed Ca-dominant surface soils, they became Mg dominant at a depth greater than 10-20 cm, and may be intractable for that reason. This includes many of the soils developed on basalt, or material derived from basalt.