The need for sorghum to beat the heat
The number of high-heat days experienced across the northern cropping belt is prompting researchers to recommend that growers reassess their approach to sorghum varietal selection, sowing date and crop management.
Research by CSIRO and Queensland Alliance for Agriculture and Food Innovation (QAAFI) at The University of Queensland shows that over the past 40 years of weather records, days with temperatures higher than 36°C have increased from about seven to more than 30 a year across the northern cropping belt.
When it comes to sorghum, research supported by the Grains Research and Development Corporation (GRDC) and the Australian Department of Agriculture (GMS-0335 ‘Climate Ready Cereals’) shows that there are significant implications of heat stress for pollen viability, even in crops that are not moisture stressed.
Project leader and CSIRO senior principal research scientist in crop adaption, Dr Scott Chapman says temperatures higher than 38°C damage the viability of a plant’s pollen which leads to decreased seed production and reduced yield.
“In a sustained heat event, up to 95% of the grain can be damaged in some plant lines,” he said at the GRDC July update in Moree.
“Varietal attributes, such as heat stress tolerance, tillering and maturity can all have large effects on yield.
“However this will depend on starting soil water, the time of sowing, crop management and the nature of the season.
“We know that sorghum seed set is reduced by high temperature effects on pollen around flowering. However sorghum genotypes do differ in their tolerance to high temperature stress and we now have an excellent screening procedure for this.”
Professor Graeme Hammer, whose team at QAAFI led the experimentation and modeling, says research has confirmed that yield cannot be estimated at the time of sowing and the superiority of specific genotype and management combinations varies from year to year depending on how the season transpires.
“The best we can do is to estimate the risks of what might happen for different scenarios given historical climate data. Sowing times in mid to late October have the highest risk of heat exposure impacts,” he said.
“The APSIM model provides our best technology for these estimates and the sorghum model has been recently updated to incorporate the latest scientific knowledge on the physiology of crop growth and development, and with this project now has a capability to model high temperature effects.”
While seasonal variability poses a challenge for northern growers, avoiding heat damage through crop management and genetic tolerance seems possible.
“Another key point is that while late plantings in December-January in Northern NSW will generally avoid the heat risk, late cultivars sown at this time risk cold conditions, which reduce yield and exposure to weather which may favour ergot,” said Professor Hammer.
“These studies have discovered potential sources of genetic tolerance to high temperature so that breeding options will still be possible.
“In the short term, growers should be able to improve yield and reduce risk through the selection of suitable sorghum hybrids and other management options, including having a spread of sowings or maturities at a single sowing to reduce the overall heat stress risk in any season.”
Prof Graeme Hammer
Professor in Crop Science & Director, Centre for Plant Science
07 3346 9463
Dr Scott Chapman, CSIRO Senior Principal Research Scientist in Crop Adaptation and Modelling
07 3214 2254
Ellen McNamara, Cox Inall Communications
0429 897 129
GRDC Project Code CSP00136, UQ0006