Fertility assessment of soils of the Mt Garnet area, North Queensland

Abstract

Surface soil samples (0-l0cm) were collected from 47 sites covering the range of soil types in the Mt Garnet area of Queensland. The soils are slightly acid, have low phosphate buffer capacity, and contain low levels of organic carbon, total nitrogen, exchangeable basic cations, DTPA-extractable zinc and copper, acid-extractable phosphorus and phosphate-extractable sulfur. In many soils, phosphate-extractable sulfur levels were higher at depth 70-80 cm than in the surface 10 cm. In glasshouse experiments, Stylosanthes hamata cv. Verano was grown on 7 different soils selected as representative of the range in soil chemical characteristics. Dry matter yield responses to phosphorus, sulfur and zinc were measured. Field experiments at 2 sites confirmed the deficiencies of phosphorus and sulfur, but not of zinc. From the results of all of these techniques, we conclude that a single superphosphate (9% P; 10% S) application of 560 kg/ha is necessary to maximise yield of legume-based pastures on these soils. However, applications equivalent to 140 and 280 kg/ha increased yield and had strong residual effects which lasted into the second growing season.