Is earlier wheat sowing the right adaptation strategy for all of Victoria? (7818)
Earlier sowing has been espoused as an adaptation strategy for maximising wheat yields by limiting heat stress during grain fill. This could also increase the risk of frost damage at flowering. Sometimes the crop is able to be sown into moisture early and sometimes it is sown dry. Dry sowing has agronomic limitations however as early weed control options are poor and unless different maturity varieties are sown all crops flower on the same day, potentially exposing you to the risks of heat and frost if they occur in the flowering or grain filling window. Also worrying, is the apparent increase in frost occurrence in these critical periods since 1995. We obtained DAFF Qld Patch Point temperature data at Ouyen, Longerenong, Tungamah and Lismore to assess the historic risk of heat and frost at different sowing dates of wheat.
We used the APSIM derivative Yield Prophet® to determine the flowering dates for Yitpi wheat (a mid maturity variety) sown at four different locations and at five different sowing dates. We counted the number of years where one or more extreme frost or heat events had occurred during flowering or grain fill over the last 125 years and converted that number to a percent chance of occurrence. We decided to look only at severe frosts of below 0oC (frosts occur at +2oC), 5 days before or 15 days after flowering and severe heat stress of a 34oC day (heat stress starts at 30oC) in the grain fill period 30 days after flowering.
At Ouyen the frost risk sowing on 25 April is the lowest of the four locations chosen, at only five years in a 100. Longerenong shows the most risk with a one in four year chance of frost. Sown on the 10th of June places north of the Great Divide have nearly zero chance of frost but a one in two year chance of heat.
This data perhaps sheds light on the success of early and dry sowing in recent years in the Mallee and North East Victoria. It suggests a small amount of caution at Longerenong for earlier sowing whilst suggesting that SW Victorian growers could benefit from trying to sow earlier than they are.