On-farm trials designed to avoid heat stress during flowering have shown yield and quality improvements, despite occurring over three successive La Nina years.

Sowing sorghum in later winter or early spring can increase yields by up to two tonnes a hectare. In seasons affected by heat stress, this can equate to an increase of $400 per hectare in gross margins.

Professor Daniel Rodriguez from the Queensland Alliance for Agriculture and Food Innovation (QAAFI) has been examining whether heat stresses at flowering could be avoided by changing the time of sowing. The answer is a resounding yes.

“When we look at the results there are only small differences in the more than 1000 points of yield data. However, when we looked at the data for sites that did have heat stress, and then looked at what would have happened if we had planted earlier, we saw differences in yield of about two tonnes/ha,” he says.

“So there are benefits, though they are not in every season. They occur in the hottest sites in the hottest seasons – but this is what we want, as heat stresses are likely to become more frequent and severe.”

Many growers have planted sorghum early for years to beat the heat. However, since 2017, a broad research program between GRDC, the University of Queensland, the New South Wales Department of Primary Industries and the Queensland Department of Agriculture and Fisheries has tested the boundaries of early sowing.

Professor Rodriguez’s results are the latest in this work. They show that not only is earlier sowing economically and agronomically sound but also highlight how more system-changing research is needed to deal with climate change.

And, with that, a change in approach to ‘e-agronomy’ research is required. Professor Rodriguez says background R&D, such as this sorghum project, could be translated into simple rules of thumb that draw on growers’ own data from soil probes and weather stations.

Professor Rodriguez outlined these topics and future research needs in his keynote address to the 2023 Summer Grains Conference, held earlier this year at the Gold Coast.

Innovative crop adaptations are needed. “Australia’s climate has warmed by about 1.4°C since 1910, leading to an increase in the frequency and intensity of extreme heat events and water stresses. This emphasises the need to ‘de-risk’ summer cropping by testing innovative crop adaptations for farmers.”

Early sowing history

Over the years sorghum growers and researchers have questioned sowing times.

Professor Rodriguez says that in the early 1990s, simulated research suggested early sowing – in spring – would not work. However, no field trials were done. “At the time the main concern was about late frosts and terminal water stresses.”

Since then, researchers have learnt that sorghum is not affected by frosts until it has six to seven leaves, and at the same time they have become more concerned about climate change.

“Our climate has warmed. The frequency and intensity of late frosts have reduced, and sorghum can germinate and emerge if sown into moist soil beds at 13˚C and increasing. We have also improved the Agricultural Production Systems sIMulator’s (APSIM) capacity to simulate crops sown outside traditional sowing windows.

“Growers needed the option to avoid those heat stresses. So, we needed to develop the technology to sow early.”

Cold questions

The project team knew of early sowing benefits. This includes higher yields, double-cropping options, additional sowing options in marginal environments, increased ground cover and – in irrigated systems – ratooning options. However, questions about cold soils and crop establishment, and yield and quality considerations, needed to be answered.

From central Queensland to the Liverpool Plains, the research showed the minimum soil bed temperature required for uniform crop emergence can be as low as 13°C and increasing. Time to crop emergence will be extended by two to three weeks.

In terms of grain yield and quality, the benefits were higher yields, lower screenings and no lodging compared with summer sowing.

Over the past three seasons of on-farm trials that yielded between 0.25t/ha to 12.5t/ha, late winter and spring sowings produced similar median yields, but outperformed yields from the summer-sown trials.

Screenings were low in general, particularly in the early sowings, indicating that early sown crops can avoid terminal water stresses typical of later plantings.

The lower screenings and no lodging in the early sown crop were associated with a lower water use between emergence and seven leaves and seven leaves and flowering; and a higher water use between flowering to maturity. This resulted in a higher water use efficiency for the early, compared with the spring and summer-sown crops.

What decisions are needed  to sow early?

Professor Rodriguez says the decision on whether to sow early or to wait needs to be informed by the availability of high-quality seed very early in the season, as well as by measuring soil temperatures and soil moisture at sowing depth.

Given that the crop will be established on residual moisture from late summer rains, and that no or little rains can be expected during late winter and early spring, soils should be at least 80 per cent full. Other factors include the presence of soil insects and difficult-to-control grass weeds in the selected field.

The team created simple rules of thumb using an artificial intelligence (AI) algorithm and observed data. The AI model found that having soil temperatures higher than 13°C was the first criterion that needed to be considered; having at least 200mm of plant available soil water was the second.

Professor Rodriguez says the fact that hybrid was not selected as a predictive variable by AI shows that there is very little difference in cold tolerance between commercial sorghum hybrids.

Cropping system implications

Quantifying the impacts of any practice change is important, he says. “The idea that ‘yield is king’ fails to acknowledge that what matters most to growers is farm profits and risks.”

Professor Rodriguez highlights an example where there is a $250/ha difference between sowing sorghum early and not doing so.

It relates to Warra-based grower Wade Bidstrup’s rotation. “Wade has already adopted the practice of sowing sorghum early, so it was good to have his experience and data to parameterise the APSIM model. It meant we could run his present rotation and compare that with a rotation that didn’t have early sown sorghum.”

Wade has been sowing early for more than 20 years. At the time, his decision was based on seeing heat-stressed crops. “In the beginning, I could see the plant getting done by heat around Christmas. I thought – what if we planted a month early? Let’s see what we can do.”

He tried sowing in early September, compared to the usual district practice of sowing somewhere between October and December.

That first time he planted with a tyne because it was so dry. “It didn’t come up that well. But we did get a decent-enough yield.” The next year the season was different, and with that planting and establishment improved.

These days Wade, who farms with his wife Sally and parents Jeff and Marilyn, checks the ambient air temperature before deciding on planting early. “If it’s a mean temperature of 15 to 16˚C, I’ll go for it. It works really well for us now.” An added benefit is water use efficiency, which is greatly improved with an early sown crop.

Professor Rodriguez says APSIM showed that sowing sorghum early gives Wade the option of double cropping into a chickpea crop. “In the rotation that has the early sown sorghum you will have more opportunities. For Wade, that equates to a median gross margin of $850/ha compared to $600/ha.”

Wade is pioneering the early planting of other crops now, too, including corn. “If the air temperature is about 11°C or 12°C on average for the day, we will plant.

“Once it was planted next to chickpeas. Frost got the chickpeas, but the corn was unscathed. Early planting corn also gives us the opportunity to dodge fall armyworm (FAW).”

Wade has also planted barley early – in March. “If it flowers before the first frost, it works out pretty well.” He would like to see more research into the early planting of other crops, particularly corn. “It yields really well, and the price is always higher than sorghum.”

System adaptation

Professor Rodriguez agrees that more research is needed into crop and system adaption, such as time-of-sowing work for a wider range of crops.

“Climate variability and ongoing climate change provide us with a clear focus and mission to increase crop adaptation to water and heat stresses.

“There is a need for more long-term R&D flagship programs intentionally designed to produce transformational outcomes on large and complex problems.

“In this project, we demonstrated the benefits of adopting best-fit combinations of agronomic management and cultivar to regions, soils and seasonal conditions.”

However, he says there is a lack of tools that can easily translate data into valuable information that supports decision-making on-farm.

“Many companies offer data management and collection systems, but these ignore systems agronomy. They lack the knowledge to translate data from sensors into action.”

Professor Rodriguez says the solution lies in integrating the data and knowledge developed by researchers using outputs from e-agronomy tools and sensors. That could provide real-time information that supports relevant and actionable decisions specifically for dryland broadacre cropping.

“Bridging this gap requires us to answer how e-agronomy can integrate systems agronomy to translate data from farmers’ soil probes and weather stations into relevant, easy-to-use and valuable information and simple rules of thumb to increase yields and reduce risks.”  

More information: Daniel Rodriguez,  d.rodriguez@uq.edu.au, Agronomic guides can be requested from d.rodriguez@uq.edu.au