It may pay to review your risk appetite and long-term planning to improve returns in low-rainfall cropping zones

Erratic profitability and changing rainfall patterns are just two of the factors that make cropping in the low-rainfall zone (LRZ) of Western Australia challenging.

However, a four-year project that has combined experimentation with modelling and economic evaluation is set to deliver new tools for growers in the LRZ to deal with these challenges.

CSIRO farming systems scientist Dr Andrew Fletcher, who leads the GRDC-supported project, says the key to success will be adopting these tools with a changed mindset that views farming systems in both a longer and wider framework.

“Low-rainfall zone farming systems are characterised by low average yields and high risk,” Dr Fletcher says.

“Terminal drought and heat stress during grain filling are also common. Growers have adopted cereal-dominant, risk-averse approaches with low use of inputs such as fertiliser.

“Crop productivity improvements for this zone may require a change of risk appetite. To address this, we have been reconsidering fallow as a soil moisture management technique for this zone, together with new early sowing options and high-value break crops (such as) field peas, lentils, chickpeas and lupins.

“But, more importantly, we have considered the performance and economics of combinations of these practices over longer-term timeframes to consider how they can be optimised to improve grower returns.”

Field experiments

Trial results at both Merredin and Hyden over four years demonstrated the importance of including break crops and fallow to improve yield and protein content of wheat.

In wheat crops grown in 2020 at Merredin, there was a 0.4-tonne-per-hectare yield increase in wheat after chickpeas, a 0.66t/ha yield increase in wheat after serradella pasture, a 0.62t/ha yield increase in wheat after fallow, and no increase in yield in wheat after canola compared to continuous wheat.

“Break crops also increased protein content of wheat, including a number of effects that persisted longer than one year. Legume pasture, in particular, gave a boost in grain protein,” Dr Fletcher says.

At Hyden there was a 0.45t/ha increase in 2020 wheat yield in a fallow/wheat/fallow/wheat rotation compared to a continuous wheat (see Table 1).

Table 1: Yields and protein content of wheat in a range of sequences in 2020 in trial 2 at Hyden (F = fallow, W = wheat and C = canola).

Economic modelling

“To consider how best to optimise crop sequences, it was crucial to consider the economics of each combination and we were able to do this using a unique industry dataset,” Dr Fletcher says.

Economic modelling using this data demonstrated that including break crops can increase profitability of rotations in the LRZ due to increased wheat yields, lower input costs and diversification of income, especially in poor seasons, which also helped to reduce risk.

Table 2 shows the calculated gross margin for various rotations in the LRZ. The mean gross margin for each rotation is shown as a measure of overall profitability and the mean gross margin in the bottom 20 per cent of years is shown as a measure of risk in each scenario.

“Take, for example, a canola/wheat rotation; it has an average partial gross margin of $262 per hectare  over multiple paddocks in multiple years and even in the worst 20 per cent  of seasons it produces $21/ha profit. In comparison, continuous wheat produces an average gross margin of $217/ha, and losses of $36/ha in the worst seasons,” says Dr Fletcher.

Table 2: Predicted partial gross margins of rotations in the low-rainfall zone of Western Australia.

Source: CSIRO

Fallow role re-examined

Long fallowing over winter was once a common practice in LRZ areas of WA, where rainfall is the main factor limiting plant production. However, as crop management improved and profitable break crops became available in the 1980s, the importance of fallowing declined. But, since then, this region has experienced a progressive decline in rainfall. As the regional climate dries further, fallowing is receiving renewed attention from LRZ growers and could provide an alternative risk management option.

Simulation modelling carried out by Dr Chao Chen, a member of the CSIRO team, has showed that fallow could increase wheat yields and profitability of the copping systems in the LRZ.

Figure 1: The mean absolute yield response to fallowing (a) and relative yield response to fallowing (b) during 1995–2019 across the wheatbelt of Western Australia.

Source: CSIRO

The greatest yield increases were in the north-eastern part of the wheatbelt, where fallow could increase wheat yield by 10 to 40 per cent.

Practical considerations

Growers in the LRZ have developed innovative farming systems to cope with the challenges they face with low and variable rainfall. For example, canola is an emerging break crop in the LRZ and growers have become adept at increasing canola areas when sowing conditions are favourable. Further improvements in the LRZ will require growers and researchers to work together to identify new profitable break crops to complement canola and develop innovative management packages to fit them into a farming system.

In order for growers to consider these more-complex crop sequences for the LRZ, they will likely have to increase on-farm storage for more seed varieties, Dr Fletcher says.

Accessible high-value legume market outlets for growers in the Low Rainfall Zone  will also be necessary.

Additional work

Further economic studies are underway. These will include calculating full gross margins for the trials at Merredin and Hyden and using simulation modelling to extend the results of these trials to other locations.

More information: Dr Andrew Fletcher, 0477347449, Andrew.L.Fletcher@csiro.au