Sorghum growers in Australia’s northern cropping belt are being urged to closely monitor crops for yield damage in the wake of record-breaking New Year temperatures.
The recent spate of hot weather coincided with a critical development phase for many crops and growers are being warned that heat can have severe impacts on yield, even in crops that are not moisture stressed.
Sorghum Plant Breeder and Team Leader of the Queensland Alliance for Agriculture and Food Innovation at Warwick’s Hermitage Research Facility, Dr David Jordan, said while the yield impacts of moisture stress particularly around flowering and grain filling were well recognised, recent research highlighted the implications heat stress for pollen viability.
Backed by the Federal and Queensland Governments and the Grains Research and Development Corporation (GRDC), the research found the most severe impacts on yield occurred when high temperatures around flowering reduced the viability of sorghum pollen resulting in reduced seed set.
“The crop is most sensitive to this type of damage in the 15-day period around flowering starting soon after the emergence of the flag leaf,” Dr Jordan said.
“During this stage periods of temperatures above 38 degrees Celsius during the day for a number of days can result in reduced seed set, with complete crop losses possible if the stress is severe enough.”
The study also showed that different varieties, including commercial hybrids, vary considerably in their sensitivity to this problem.
Dr Jordan said the impact of the recent high temperatures on individual crops would vary depending on the growth stage of the crop, varietal sensitivity and the duration and severity of the high temperatures, and that on-going management decisions would need to be made on a case-by-case basis.
The heatwave conditions have forced some producers to consider baling or grazing their affected crops rather than taking them through to harvest.
While a failed grain sorghum crop may offer high grazing value, its utilisation requires careful management to minimise the toxic and potentially fatal effects of prussic acid, according to Landmark senior agronomist Paul McIntosh, Toowoomba.
Animals grazing grain sorghum require sulphur in a detoxification process to convert prussic acid to the non-toxic thyocynate and as grain sorghum varieties can be deficient in sulphur, Mr McIntosh recommends supplementing the animals with sulphur blocks well prior to and during grazing.
“Supplementing with sulphur alone won’t eliminate the risk of toxicity but it will reduce it considerably,” Mr McIntosh said.
“Having a mix of pasture grass available at the same time is of benefit, as is not allowing hungry cattle to have uncontrolled feeding in a paddock of failed grain sorghum, particularly if the failed crop is in the early growth stages.
“For example, crops under 12 inches in height are of higher risk than those at flag leaf stage. Even baling for hay is not going to eliminate prussic acid problems in these at risk plants.”
Caption: This image shows the impact of high temperatures in a controlled environment chamber on seed set in a particular sorghum line.
Dr David Jordan
Sorghum Plant Breeder & Team Leader QAAFI
Hermitage Research Facility
07 4660 3622
Paul McIntosh, Senior Agronomist, Landmark Toowoomba
Michael Thomson, Senior Consultant Cox Inall Communications
07 4927 0805, 0408 819 666
GRDC Project Code