Optimising harvest operations against weather risk

Abstract

Most wheat in Australia is harvested at a maximum moisture content of 120/0 wet basis (w.b.). Delaying harvest until the grain is naturally dried to 12% results in yield and quality losses. Losses due to rain on the mature crop cost the grain industry around &A 30 million annually (&A 1 = &US 0.75). These los ses are significantly higher in the northern wheat belt of Australia due to a dominant summer rainfall which coincides with the harvest period. If a wet season can be predicted, growers could reduce grain los ses by implementing strategies such as early harvesting, contract harvesting, additional grain drying and harvesting at a faster rate.

Weather prediction is possible several months ahead by the analysis of sea surface temperature and air pressure differences between Tahiti and Darwin, as identified by the Southern Oscillation Index. Long range weather forecasts could enable farmers to maximise profits by altering their management practices according to seasonal variations in rainfall.

This paper examines the interactions between weather, crop, machinery selection and management practices during wheat harvesting in northern Australia. A simulation model was used to investigate the effect of harvesting at high grain moisture content, then drying artificially to reduce field and quality losses. The model predicts that additional returns of up to $A 140 ha^–1 are possible by adopting long term strategie harvesting decisions in the northern wheat belt. Returns may be further increased by $A 20 to $A 40 ha^–1 through optimising harvest operations during each season. Optimum machinery capacities and harvest strategies for a range of crop areas are outlined.