Two contrasting seasons that resulted in waterlogged conditions in southern Western Australia have provided valuable data to help inform growers’ responses to  such circumstances.

Sowing crops later in the growing season can provide opportunities to manage climate variability – however, if this is a response to early season waterlogging, the decision to sow late can be stressful. Timeliness is the essence and each season can be a different scenario.

The south coast region of Western Australia is prone to waterlogging events that can severely impact grain production. In the early 2020s, growers in that region had struggled with consecutive wet seasons.

Through GRDC’s National Grower Network, two research projects were deployed in 2022 and 2023 in response to grower requests. The aim was to provide growers and advisers with greater confidence to make decisions to grow a cereal crop later in the season.

Led by Dan Fay from Stirlings to Coast Farmers (SCF) and in collaboration with South East Premium Wheat Growers Association (SEPWA), trial sites were in the Albany Port Zone (Green Range and Needilup in 2022 and Gnowellen and Takalarup in 2023) and Esperance Port Zone (Munglinup and Condingup in 2022 and Dalyup and Condingup in 2023).

Mr Fay says the waterlogging conditions were ideal over the two years to compile datasets on late-sown cereals that could form a useful legacy reference for growers to make better-informed decisions in these circumstances.

About the trials

In both 2022 and 2023, four small plot trials were sown along WA’s south coast high-rainfall zone (HRZ). These trials included three barley and two wheat varieties, with two nitrogen strategies applied to each variety across three times of sowing (TOS).

Mr Fay says in 2022 – a decile nine rainfall year with a large amount of summer rainfall – the cereal yield results were outstanding, likely due to each TOS treatment being seeded into a full soil moisture profile and the cool, wet finish to the season (Figure 1).

Yields ranged from greater than 7t/ha for crops sown late August to yields of greater than 5/ha for crops sown late September.

“The 2023 season, on the other hand, was quite different, a decile five season overall, with a large rainfall event early in the season and then very little for the rest of the season. It added another dimension to our dataset for growers and some different learnings.”

Mr Fay says yield results were lower with initial severe waterlogging being followed by a hot and dry season finish.

“The Albany TOS1 treatments and the first Dalyup trial site were terminated – seed either burst or was waterlogged. Cereal yields from the Condingup site, particularly TOS1, were good given the season, with barley achieving more than 4t/ha. The highest grain yields at the Takalarup and Gnowellen sites were achieved with Rosalind barley and were just above 1.5t/ha and 2.5t/ha, respectively.”

Each trial site in 2022 included:

• three times of sowing (late August, mid-September, late September);
• two wheat (Vixen and Scepter ) and three barley varieties (Maximus , RGT Planet and Rosalind ); and
• two nitrogen treatments (high – 80 units of nitrogen, low – 40 units of nitrogen).

Trials in 2023 consisted of:

• three times of sowing (late July, mid to late August, mid-September);
• two wheat (Vixen and Scepter ) and three barley varieties (Maximus , Rosalind , Neo – Albany, Combat – Esperance); and
• two nitrogen treatments (high – 80 units of nitrogen, low – 40 units of nitrogen).

To illustrate the differences in the two season, Mr Fay says that from the date TOS3 was seeded in 2023 at Takalarup to the date of harvest, the site received 42.4 millimetres of rain. In 2022, the same location received 269.2mm over the same period.

Figure 1: Monthly rainfall at each of the trials sites from August to December 2022 and 2023

Source: SCF

“Essentially, in a two-year period, the area around Takalarup has been faced with both the best and worst-case scenarios for late seeding of cereals after waterlogging.”

Learnings

Although the 2023 season was more challenging than 2022, there were more learnings to take away from the 2023 data, Mr Fay says.

“Firstly, in conditions where the finish is going to be tight, or more likely where growers are unsure of how the season is going to play out, the 2023 data supports utilising shorter season varieties. Vixen , Maximus and Rosalind , all out-yielded the longer season varieties. This was not the case for 2022 where variety maturity had less influence.

“Quicker-maturing varieties can quickly move through growth stages when seeded so late in the season, as they are primarily driven by the increased daylight that is available in the spring.

“In 2023, this reduced the crops susceptibility to heat stress and water stress during the grain fill period by having this occur earlier in the season.”

Another important finding was that the varying nitrogen rates had no significant impact on grain yield or protein content. Mr Fay says this is likely because the 2023 yields were too low for nitrogen to be a limiting factor and the shortened growing season did not provide enough time for the crops to absorb and use the extra nitrogen. Also, since the crops were planted so late, there was probably extra nitrogen in the soil from the decomposition of previous residues.

For growers to maximise the chances of growing a profitable crop after a period of waterlogging, it is important to get on the paddock to seed as soon as it is safe.

However, gauging this timing is a challenge as TOS1 at both Gnowellen and Takalarup highlights the risk in seeding too soon after waterlogging. TOS1 at both these locations were seeded when the soil was saturated but trafficable.

“Unfortunately, this was followed by a larger-than-expected rainfall event that occurred in the week after seeding. As a result, the seed burst and the plots needed to be terminated, highlighting the continuing challenges and risk of cropping in these situations for growers,” Mr Fay says.

“The difference in barley yields to wheat yields across the 2023 trial sites is likely a result of the barley being primarily driven by photoperiod and maturing quicker than the wheat, which suffered late season heat and drought stress.

“Interestingly, grain yield at Condingup for TOS1 – sown 25 July – showed barley significantly out-yielded wheat. In TOS3, the trend was reversed with wheat significantly outperforming barley.”

He says this is likely due to the wheat having a longer vegetative period, which allowed it to build more biomass to drive more yield at this later sowing time compared to barley, which ran too quickly to head.

A basic economic analysis was conducted on the 2023 crop performances and showed that the sooner a late-sown cereal can be ‘successfully’ established after waterlogging, the better. It should be noted that the analysis included the cost of having already attempted to sow a cereal that had failed.

In most cases in this analysis, even where a loss was made, the loss would have been more significant had not some of the losses been recouped by a second late sown cereal.

Decision tools

The data collected over the two very different seasons has built grower confidence in sowing cereals late and will provide an ongoing reference for decision-making in challenging seasons going forwards.

Reports from these studies are available from the GRDC’s On Farm Trials portal, Stirlings to Coast Farmers and SEPWA websites.

More information: Dan Fay, dan.fay@scfarmers.org.au