Impacts of management on soil biota in Vertosols supporting the broadacre grains industry in northern Australia

Abstract. The grain-producing regions of northern New South Wales and southern and central Queensland are characterised by cropping systems that are strongly dependent on stored soil moisture rather than in-crop rainfall, and tillage systems that are increasingly reliant on zero or minimum tillage. Crops are grown relatively infrequently and crop rotations are dominated bywinter and summer grains (wheat [Triticum aestivumL.] and sorghum [Sorghum bicolor L. Moench], respectively), with smaller areas of grain legumes and cotton (Gossypium hirsutum L.). The grey, black, and brown Vertosols represent the more productive soils in the region under rainfed cropping, and are the focus of work reported in this study. Soil samples were collected from surface soils (0–0.30m) across the region, utilising sites of long term tillage and residue management studies, fertiliser trials, and commercial fields to enable an assessment of the impact of various management practices on soil biological properties. A number of biological and biochemical parameters were measured (microbial biomass C, total organic C and labile C fractions, total C and N, microbial activity using FDA, cellulase activity, free living nematodes, total DNA and fatty acid profiles), and the response of wheat, sorghum, and chickpea (Cicer arietinum L.) to steam pasteurisation was assessed in glasshouse bioassays. The objective wa