An alternative method for assessing the value of the Southern Oscillation Index (SOI), including case studies of its value for crop management in the northern grainbelt of Australia

Abstract

Previous studies have identified extra profit that could result from selecting management options according to particular phases of the Southern Oscillation Index (SOI). Those studies identified optimal decisions for each phase and the value of these decisions. However, this may have overestimated the value of SOI-based management through a lack of data for independent evaluation. This study compares the previous approach with a new method based on a simple sampling technique (analogous to leave-one-out cross validation) that estimates the range of future outcomes when independent validation data are not available. The new method gave much-improved estimates of the mean and variance of the value of the SOI for management. In studies involving wheat-growing in southern Queensland, this method indicated that management according to the April–May SOI phase yielded either small long-term increases (in 4 of 6 cases) or decreases (in 2 of 6 cases) in profit. There was considerable heterogeneity among phases, and the annual variance of the outcomes was large relative to the long-term average value in all 6 cases. Consequently, unless a strategy is applied long term (at least 10 years), there is a relatively high likelihood of higher or lower profit than for non-strategic management. The likelihood of increased and decreased short-term profit is approximately equal. In all 6 case studies, the long-term average economic value of SOI-adjusted management was less than, or equal to, the economic value of 1 mm of extra plant-available soil moisture at sowing.