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Published: 3 Jun 2022

Recent work with the Grains Research and Development Corporation (GRDC) subsoil manuring field trial at Nile, in Tasmania’s east, has found promising results with the re-use of animal and green manures in the dense subsoil of a texture contrast soil.

The first two seasons with crops of barley and canola showed yield increases of 30-55% and in 2020-21, the effects of manure pellets applied in the subsoil (deep manure) have continued to demonstrate yield benefits of 17% (Figure 1) despite higher rainfall. These results are part of a five-year trial to determine how long the benefits of subsoil manuring might last for, under what conditions and how soil physical properties might be improved. Further research will be carried out this year to determine the treatment’s effects on soil water infiltration, water holding capacity, and nutrient contents.

Sustained benefits of subsoil manure treatments on barley (RGT Planet) grown in 2020/21. Different letters indicate results that were significantly different.

While these results are exciting at the field scale, the broader adoption of circular economies is difficult to translate into actionable and profitable changes in agri-food systems. Reasons for these difficulties include the linear nature of economies, public perception of sewerage recycling, and the complexities of agricultural systems compared to other industries. The larger potential benefits to soil health of recycling nutrients are largely unknown.

Soil core of subsoil manure layer of the Deep manure treatment (photo by Peter Johnson).

Tasmania is well positioned to continue to break new ground in this space as a world leader in nutrient management innovation. The wide variety of agricultural commodities in relatively close proximity, and broad range of soil types, makes it a great candidate to explore the opportunities and limits of a circular nutrient economy. As an island state, there is urgent need for circular solutions to reduce transport costs and improve local resilience to shocks in supply chain, like the recent fertiliser and fuel price hikes.

Other new research in the circular economy is happening at the University of Tasmania, such as the Sea Urchin Fertiliser Project. Many other positive actions of waste reuse are also happening all over the state such as vegetable waste being fed to livestock, fish poo from hatcheries being used in compost, repurposing aquaculture waste, and re-use of winery by-products. We are looking to bring together a larger network of people working in this space in Tasmania to further catalyse new industry and products, boost agricultural production, and reduce emissions and pollution.

Contact Bianca Das to discuss subsoil manuring, soil fertility, or circular nutrient economy network collaboration at

About the author

Bianca Das recently joined the Tasmanian Institute of Agriculture as a soil scientist (researcher and lecturer) based in Launceston. She is currently leading the subsoil manure trial. The trial is part of a larger GRDC project – more information can be found here.

Special thanks to Geoff Dean, Pete Johnson, Marcus Hardie, Meixue Zhou, and Caroline Mohammed for work in establishing and supporting the subsoil manure trial at Nile.

This article was published in Tasmanian Farmer newspaper on 27 May 2022.