Quantifying Potential Benefits of Strategic and Tactical Fallowing in Western Australia

Continuous cropping has become prevalent in the low rainfall zone (LRZ) of WA as sheep numbers have declined. Fallowing is topical after playing a significant role in the success of the 2024 cropping season in WA. The final Grain Industry Association of Western Australia (GIWA) Crop report on the 2024 season (issued February 2025) states that the grain growing season ended up with the third largest tonnage on record.

This is in part attributed to the impact of fallowing in the previous season as stated in the report; “2024 was a lower decile rainfall year than 2021 and 2022, but it had a very high area of crop sown on fallow. The area of fallow going into 2024 was around 1 million hectares where it normally is around the 300,000ha mark and this helped crops yield close to or exceed long term average grain yields in the lower rainfall regions south of the Geraldton port zone. This high area of fallow in some degree insured those regions by limiting their risk from a low rainfall year.”

Long (winter) fallowing can be either strategic or tactical. In strategic fallowing the decision to fallow is made in advance and implemented regularly to manage climate risk. In tactical fallowing the decision to fallow is more reactive, based on the evolving season and can be related to seasonal risk mitigation or temporal changes in weed and disease burdens. Although many growers are implementing a (winter) fallow in their farming systems, a large number remain uncertain and are seeking scientifically backed advice on several aspects of fallowing.

Recent National Grower Network (NGN) investments from GRDC have provided some insights into the costs and benefits of fallowing. But there are complexities affecting the decision to fallow and knowledge gaps on fallowing were still a priority issue raised at several NGN forums in the LRZ of Western Australia. This investment aims to provide growers with technical guidelines that provide actionable insights for considering strategic and/or tactical fallowing approaches. Detailed field-based measurement, bioeconomic analysis, and communication and extension will seek to answer questions on key aspects of fallowing such as:

• what is the optimal herbicide use pattern in chemical fallowing or brown manuring,

• what is the impact of soil types in selecting areas to fallow,

• is there an optimum percentage of area to fallow in a particular season,

• how does one decide on the appropriate crop species to sow after fallowing, and

• how does one accurately assess the economics of fallowing.

A behavioural science component has been included to address the decision-making process in choosing to fallow and understanding the type of tool(s) that growers would like to use in supporting decisions for either strategic or tactical fallowing.

A review of previous and current research projects that include aspects of winter fallowing (including brown manuring) will be undertaken. The review will assist in the design of new field experiments and subsequent bioeconomic analysis. By addressing knowledge gaps identified on both strategic and tactical fallowing it is expected to give LRZ growers the confidence to implement fallow management and in turn potentially reduce yield variability.