Management of the major chemical soil constraints affecting yields in the grain growing region of Queensland and New South Wales, Australia - a review

In the grain growing region of Queensland and New South Wales, Australia, crop production occurs predominantly under semiarid, rainfed conditions. Vertosols dominate the soils used and many are prone to structural problems. In this region, providing that crop nutrition is adequate, optimising yield is largely dependent on maximising the infiltration, storage and plant use of soil water. Soil constraints such as sodicity, salinity, acidity, subsoil compaction and surface sealing can limit these processes, leading to high yield losses. This review examines management options to treat these constraints, focusing on management where multiple constraints exist, and where these occur in the subsoil. The main strategies reviewed include (a) use of gypsum to treat sodicity and lime to treat acidity, which can lead to yield increases of >100% in some circumstances, (b) cultivation or deep ripping to break up compacted sodic layers and surface seals, (c) incorporating soil organic matter to improve conditions for plant growth and (d) selecting species, cultivars and management practices most appropriate for constrained sites. Future research must be directed to improving the profitability of ameliorant use for sodicity by increasing our understanding of how to identify soils responsive to ameliorants, and which combination of ameliorants will be cost effective when sodicity occurs in combination with other constraints. In addition, research needs to target ways to economically apply ameliorants in subsoil environments, and better identify which crop species or cultivars are productive on constrained sites, particularly those with multiple constraints.