Growers concerned about the yield effects of climate change are advised to time their seeding to closely match shifting rainfall windows
Two CSIRO farming system modellers, Dr Jeremy Whish and Dr Elizabeth Meier, have been examining northern sorghum production in response to climate change’s rainfall and temperature effects.
Dr Whish says a key concern among northern grain growers is that climate change has not only reduced sorghum yields, but it could shift production to areas where the climate is cooler and less variable.
To address these concerns, he and Dr Meier reviewed local, annual and growing-season climates and associated sorghum production and compared these results to other production areas.
“We wanted to see how or if things have changed,” said Whish.
In general, there was an overall reduction in yield potential. Although some specific sowing dates at a few sites showed yield increases, due to a shift in the timing of rainfall and extreme temperatures, the current most productive sorghum growing regions remain the same.
However, there is still room to reduce the yield gap in traditionally high-yielding areas. “Good agronomy and the use of robust soil water triggers at sowing will help maintain profitable returns under changing climates,” Dr Whish said.
The work looked at the climate from central Queensland to southern NSW. Dr Whish says the aim was to see whether the temperature had changed and if so, whether crops had been affected. Finally, how could this change be managed.
Current climate was compared with historical climate using a ‘climate normal’ approach, with 30-year time periods (1958–87 and 1988–2017) examined. A production simulation in response to a range of initial soil water and sowing dates was then done using the Agricultural Production Systems sIMulator (APSIM). This sought to identify whether changing management practices could mitigate the effect of any changes in climate.
The climate results showed that most areas were experiencing reduced rainfall and a continual increase in heat and extreme temperature days.
What does climate change mean for yields?
Dr Whish said that a changing climate is affecting sorghum production. Higher temperatures increase a crop’s development rate and the amount of water it transpires. “If rainfall remains stable or decreases, then this will increase the chance of moisture stress occurring.”
However, if the crop’s growing period can be matched to the timing of rainfall, then it may be possible to maintain or increase crop grain yield, despite an annual rainfall reduction.
High temperatures around flowering can also significantly reduce sorghum grain yield and is having an effect. The difference in the number of days with temperatures in excess of 35°C increased between the past 30-year climate normal period (1958–87) and the more recent one (1988-2017).
The increase in days with extreme temperatures was greater in the west, especially for crops sown between October and November. In the east, there was a general increase in the number of days with extreme temperatures for all sowing dates before December.