Grain maize was the highest-yielding and most-profitable irrigated crop tested in a project that explored the true economic yield potential of crops grown in south-eastern Australian irrigated farming systems.

However, the summer crop also used the most irrigation water.

The ‘Optimising Irrigated Grains’ (OIG) project undertook more than 60 individual trials in six crops annually during 2020–22. The trials at two major Irrigated Research Centres – Kerang, Victoria and Finley, southern New South Wales – were undertaken by Field Applied Research (FAR) Australia and the Irrigation Farmers Network (IFN), formerly the Irrigated Cropping Council. The aim of the GRDC-supported research was to identify gaps in knowledge about irrigation potential.

The other crops tested were the winter crops barley, canola, chickpeas, durum and faba beans, all chosen because there is less knowledge about their upper-end yield potential under irrigation. This is particularly important given newer germplasm, management advances and innovations in soil amelioration. Research also evaluated crop suitability for specific irrigated regions.

Crop performance

The project team analysed both the highest yields and associated gross margins to determine the most-profitable crops grown during the research, with commodities based on 2023 grain values.

IFN trials manager Damian Jones says that although grain maize was the highest-yielding and most-profitable irrigated crop, irrigation water use and associated costs always need to
be factored in.

“Maize does not always turn a profit and the problem is mostly to do with the water market volatility. In the first year of the project, we were paying $932 a megalitre (ML) for water. So, using more than 9ML a hectare at this price was not profitable.

“But when water was $70/ML last season, in conjunction with good grain prices, then it was quite profitable. This is why we encourage irrigators to do some quick sums that reflect the current season’s commodity prices and costs to ensure they are profitable and not work on assumptions.”

The lead researcher, FAR Australia’s managing director Nick Poole, concurs. “Interestingly, in our first year of trials with grain maize at Peechelba, in north-eastern Victoria, it was difficult to find growers to host, with water’s high price and the large amount needed for summer crops.”

To put the amount of water required into perspective, in the trial’s driest year – 2020 – winter crops typically used two to 4.3ML of water on surface/flood irrigation and 1.25 to 2ML under lateral overhead irrigation. This compares with six to 10ML for maize.

Winter winners

Durum was the top performer at Kerang, while canola performed better at Finley.

FAR Australia research manager Ben Morris says canola yields at Finley were more than five tonnes per hectare. “It was the most-reliable crop, achieving more than 4t/ha in all years at Finley. In 2020, when cereals and pulses struggled with disease and waterlogging thanks to more than 200 millimetres of rain in October, canola achieved 4t/ha in two trials.

“If you have fertile soil and establish more than 25 plants a metre using an appropriate hybrid in a well-drained irrigation bay, you are well on your way to success with canola.”

However, establishment was a challenge in poor-draining bays. Canola planted less than 100 metres away in a surface irrigation bay was autumn-irrigated and follow-up rain proved too much for the young crop to handle. This resulted in low establishment and yields less than 1t/ha.

Barley was reliable, although gross margins did not match those of canola and durum.

Both faba beans and chickpeas suffered immensely in 2022’s wetter conditions. Chickpeas proved very sensitive to less-than-perfect drainage and need well-managed disease control strategies to yield well.

However, Mr Jones says pulses remain an exciting irrigation prospect. “Part of the reason for looking at pulses beyond faba beans is the marketing and the variability of prices. That said, fabas do offer benefits beyond the grain yield.”

Nick Poole says in the first year it was difficult to find growers to host maize trials due to the cost of water. Photo: courtesy Ben Morris

Growing a durum wheat crop after faba beans could minimise crown rot. “They add nitrogen to the system. We would measure 140 to 170 kilograms of nitrogen/ha in the soil to 60 centimetres following faba beans. Pulses also play a major role in maintaining our soil organic carbon levels.”

While both researchers are excited by University of Tasmania modelling that suggests 11t/ha faba bean yields are possible, they are equally excited by the more than
7t/ha achieved during the project.

“I think the key point that came from the project was the need to get our plant population right – at least 20 plants per square metre and closer to 30. I think this is rarely achieved in commercial crops due to the difficulty in getting enough beans through the machine at normal sowing speed,” Mr Jones says.

“So, is ‘slow and steady wins the race’ the new mantra for irrigated faba bean growers?”

Canopy calculations are positive, he says. “We developed canopies of between 15 and 20 tonnes of dry matter per hectare. Maths shows that, in theory, we could achieve 11t/ha.

“I think we have moved beyond fabas being described as ‘failure beans’, but at times I describe them as ‘frustrating beans’ and on the odd occasion as ‘fabulous beans’.”

The team’s excitement about irrigated chickpeas was tempered by 2022’s wet spring.

“After the first two seasons of the project, I was on board with irrigated chickpeas,” Mr Jones says. “We were exceeding 4t/ha with pre-irrigation and one spring irrigation at the start of flowering. But with the wet spring of 2022 and the soil being held consistently near field capacity, podding was very poor with unfortunately no harvest data due to flooding.”

La Nina conditions

The research trials took place when mostly La Nina weather patterns prevailed, and it is important to recognise that when reading the guidelines.

These three years were relatively mild seasons compared with the previous three years and the cooler spring temperatures were ideally geared for testing the upper range of yield potential.

However, Mr Poole says those conditions and subsequent results come with caveats when compared with seasons with both higher spring temperatures and higher water prices.

Although La Nina conditions were prevalent, rainfall patterns across the three seasons were very different. At Kerang, rainfall amounts were decile 2, decile 6 and decile 10 across the three project years. At Finley, as much rain fell in October 2022 as what fell in 2020’s whole growing season.

Mr Poole says 2022’s weather patterns did not allow irrigated crop evaluation. “After initial early spring applications, no further irrigation was required.”

The cloudy conditions also allowed the team to explore the influence of solar radiation and spring temperatures on irrigated crop performance using the photothermal quotient (PTQ) or cool sunny index calculations.

Cooler temperatures and sunnier conditions during the critical period prior to flowering leads to greater growth during the period when grain and seed number is being determined, leading to more potential grain sites and a higher yield potential provided the crop is not subject to other stresses such as frost or moisture stress.

“A higher PTQ during the critical period can result from both higher radiation and lower temperatures. For example, in 2021 many regions experienced higher solar radiation than that experienced in the same period in 2022. This led to higher yield potential and realisation in 2021 than in 2022.”

Table 1: Highest project yields – Finley, NSW (machine harvested).  Grain maize, Peechelba, Victoria.

Table 2: Highest project yields – Kerang, Victoria.

Source: Good Management Guidelines for Irrigated Crops: 2020 to 2022

*Gross margin does not include cost of water as this is seasonally dependent

**This yield was not machine harvested but was a hand harvested crop.

More information: Nick Poole, nick.poole@faraustralia.com.au; Damian Jones, damian@irrigationfn.com.au, Good Management Guidelines for Irrigated Crops, FAR Australia, Irrigation Farmers Network