Trials comparing sorghum (left) and mungbeans at Pampas, south-west of Toowoomba, Queensland. Photos: Dr Lindsay Bell, CSIRO

Summer crops such as sorghum, cotton and mungbeans offer Australian growers options for diversifying rotations and managing weeds and diseases, and are a buffer against seasonal volatility.

Their viability, however, hinges on regional climate patterns, soil moisture availability and strategic planning.

Dominated by summer rainfall, the northern region more naturally supports dryland summer crops, which are typically sown from August to January with harvests stretching into autumn.

In the southern and western regions, Mediterranean climates with limited summer rainfall restrict options. However, changing climate patterns have promoted research in these regions.

CSIRO Agriculture and Food Principal Research Scientist Dr Lindsay Bell says cotton, sorghum and mungbeans are the most common summer crops in the northern region, although some growers also produce sunflowers, maize or niche crops such as millet.

Mungbeans are also being explored in the southern region, while in the western region;a summer legume is being considered.

Summer crop benefits

Dr Bell says a balance of summer and winter crops in the crop sequence, where the regional climate or particular seasons make this possible, has benefits for managing weeds, disease, chemical resistance and risk, as well as spreading farm operations across the year.

“In regions with high variability of rainfall occurring over summer and winter, rather than everything relying on winter crops, having a portion of a program as a summer crop provides the capacity to capture favourable summer conditions,” he says.

Dr Bell says research has shown significant profitability benefits (Table 1) from having a diversity of summer and winter crop options in the system. However, profitability depends on strategically considering the impact or profitability of the sequence of crops rather than individual crops grown in a particular season.

Table 1: Economic comparison of cropping systems over 8 years in Northern Farming Systems trials

Source: Dr Lindsay Bell, CSIRO

Moisture the driver

Efficiently transitioning from winter to summer crops and back is a critical challenge.

“The challenge is fitting summer crops into your farming system in a way that gives you some upside, but doesn’t have a downside,” Dr Bell says.

CSIRO Agriculture and Food Principal Research Scientist Dr Lindsay Bell inspects a maize crop at Pampas, south-west of Toowoomba, Queensland, in March 2024. This crop was able to capitalise on a late sowing opportunity and high moisture conditions in early February to produce a highly profitable crop. Systems that remained fallow lost moisture to evaporation.

Transitioning between summer and winter crops requires either a long fallow of 9 to 12 months to build sufficient soil moisture. Or it requires double cropping where a crop is sown within 4 months of harvesting a winter crop.

Dr Bell says soil moisture levels and sowing conditions should drive transitions. Because summer crops are growing when evaporative demand is higher, they often require more soil water to be stored as a safeguard against rainfall deficits.

“For example, it is widely appreciated that a long fallow and high soil moisture reserves of about 200 mm of plant-available water are required for dryland cotton,” he says. “Our research has shown sorghum crops require about 150 mm of plant-available water to maximise water use efficiency.”

Consequently, cotton and sorghum typically require a fallow of more than 6 months to accumulate sufficient moisture.

However, legumes with a lower water requirement, such as mungbeans or chickpeas, can be used as a double crop after winter cereals or sorghum. This works when there is more than 80 mm of plant-available water.

It can allow higher crop intensity and mitigate the costs of long fallows when transitioning between summer and winter crop phases.

Legacy and economic impacts

With a range of summer crops available, the decision generally comes down top their relative profitability or role in the farming system.

“Research has shown that while an individual crop may look better on paper, it is important to consider the whole crop sequence,” Dr Bell says.

Seasonal comparisons in farming systems research in the northern region have found a sequence of sorghum/chickpeas generates similar or slightly higher gross margins to a dryland cotton crop.

Mungbeans are known to need less starting water and leave more residual water than sorghum, so there can be advantages for following crops. But research has shown mungbeans can be problematic for increasing populations of root lesion nematodes (Pratylenchus thornei) and charcoal rot (Macrophomina spp.), particularly when grown as a double crop after other susceptible crops.

The research also highlighted other less commonly used summer crops, such as sunflowers and maize, can perform favourably and offer wider sowing windows – earlier in spring and later in summer – than is possible for sorghum or cotton.

Farming systems trials comparing cotton (left) and sorghum at various sites in the northern region between 2015 and 2025 have shown that while cotton crops have higher individual gross margins than sorghum, there is often a legacy of lower yields in subsequent crops and/or longer fallow periods required before the next crop in the sequence.

Southern considerations

With changing climate patterns, including a rise in summer rainfall events in southern Australia, the potential of summer crops in these environments has been a topic of debate.

To complement field trials in the southern region, a risk analysis by Agriculture Victoria, CSIRO and La Trobe University explored the potential for using mungbeans in southern NSW and Victoria.

Dr Bell, who led the modelling, says the biggest opportunity might lie with mungbeans after a winter hay crop terminated in September. This would provide a wider sowing window and more chances to accumulate moisture over summer.

But these crops would not be a regular component of the farming system, with suitable sowing conditions and soil moisture only occurring one in 3 to 4 years, even in the medium to high-rainfall zones of southern NSW or northern Victoria.

“Otherwise, in lower-rainfall regions or following winter cereals, there is a very narrow window after harvest, and conditions rarely occur when it is feasible to sow a summer crop,” Dr Bell says.

Western options

The opportunity for producing summer crops in the WA wheat belt is also limited, mainly because of climate.

CSIRO Farming Systems Senior Scientist and N-ABLE Project lead Dr Andrew Fletcher says it is normally one crop a year.

“The typical winter crops are wheat, barley, canola, lupins and oats, mixed in with livestock in that system,” he says. “There are some annual pastures, but it’s very much a Mediterranean winter annual-based system.”

Dr Fletcher says research is underway to investigate the potential for summer legume crops that could be terminated to provide nitrogen for the next year and reduce reliance on synthetic fertilisers.

“We’re not thinking that we can grow and harvest too much in the way of grain,” he says. “It’s about building diversity in the system; getting nitrogen fixing legumes into the system.”

WA growers have traditionally struggled with legume crops. Lupins are well-suited to most soils but the area under production has declined because more growers are turning to canola as a more profitable break crop option.

Unfortunately, the first 2 years of the WA Agricultural Research Collaboration (WAARC) N-ABLE project – a co-investment with GRDC – being undertaken by Stirlings to Coast Farmers have been some of the driest on record, which has hampered trials.

“That highlights the risk,” Dr Fletcher says. “It’s definitely not an every-year thing. It might only be one year in 5, depending on rainfall.”

As a result, researchers are now looking at the potential for an autumn-sown legume to be grown for 3 months, then terminated early and sown to a spring cereal crop.

Dr Fletcher concedes that is not an option for most of the WA grainbelt but might succeed in the high-rainfall zone, which has a longer growing season and more rainfall.

“The reason that might be useful, obviously for us, is that the legume is a source of nitrogen,” he says. “But it might also give us some different weed control options, if you could make that system work, because you get another chance to knock all the ryegrass out before you put in your spring cereal.”

This article appeared in GroundCover