Example 2: Wheat on the Darling Downs
Consider a second example for a farmer near Dalby planning winter cropping options. Planting rains are delayed until the end of June and the SOI phase for May–June was consistently near zero (as in 1999). Planting rains fall at the end of June but it is late in the season, and a shorter growing season may mean lower wheat yields. It might therefore make sense to sow part of the winter cropping area to chickpeas, and set the rest aside for spring sorghum.

The deep clay soil on this property has a PAWC of 230 mm, and the soil profile is two-thirds full due to the low autumn rainfall. A medium variety of wheat is sown with 100 kg/ha of available nitrogen, including the nitrogen stored in the soil profile.

A box plot analysis reveals that late wheat crops in this area are slightly riskier with a near zero phase than with the other phases, though expected median yields are similar for each phase and quite reasonable at 2.5 t/ha. An analysis of nitrogen application rates and varieties (not shown) demonstrated little potential to enhance yields.

For chickpeas, a near zero May–June phase means lower median yields than positive or rising phases. Unlike wheat, a near zero phase is not associated with a high probability of low chickpea yields compared to the other phases, and only the positive phase is associated with a low probability of low chickpea yields.

With a May–June SOI phase consistently near zero, the outlook for sorghum sown in September is encouraging, with high expected median yields and only a moderate risk of low yields.