The Reality of Soil Carbon in Sandy Soils
This month on Wheatbelt NRM in the Field, host Aimee Mouritz sat down with Professor Richard Bell from Murdoch University and Soil CRC to discuss soil carbon and what practical change could look like for farmers in the Wheatbelt.
The episode focused on Professor Bell’s Soil CRC project, “New Farming Methods to Sequester Soil Carbon, Reduce Greenhouse Gas Emissions and Improve Soil Fertility,” supported through the Cooperative Research Centre for High Performance Soils.
Setting out the key challenges facing growers working in Wheatbelt sands, Professor Bell explained that “The first thing I would say is that we need to recognise that soil organic carbon is continually breaking down. Something like 2% of soil organic matter would break down in a year.”
That constant breakdown means building soil carbon is not just about adding inputs but first maintaining what is already there.
Professor Bell also noted the structural challenges that farmers are facing in trying to improve soil carbon stocks over time.
“Even if you do nothing, you’re losing carbon year by year.”
Four pathways to building soil carbon
During the episode, Professor Bell outlined four main approaches that underpin most strategies to lift soil organic carbon in farming systems.
“One is slow down decomposition,” he said, highlighting practices such as no-till and clay addition.
The second pathway is increasing external inputs. “That could be compost or manures, if they’re available,” Professor Bell added, while also noting transport costs often limit how widely these can be used.
The third is increasing crop biomass. “That is grow more carbon on the soil,” he explained, linking this to improved crop performance and more residue and root growth returned to the system.
The fourth approach focuses on depth: “The upper 5 even 10cm may be already relatively saturated in carbon and so to build more carbon you often have to think about how you can get it into the subsoil.”
What are trial sites showing?
Across multiple sites, Professor Bell highlighted that the work focused on sandy soils, using different constraints depending on the location.
At a West Midlands site on a red loamy sand, he described a response to soil loosening practices. “There we’ve found a good response to deep tillage, both mole boarding and spading.”
Compost also showed benefits at that site said Professor Bell, illustrating that they got a response in that trial to about 10 tonnes of good quality compost.
At another site near Balaring, rotation effects stood out more than soil amendments. Professor Bell stated that the best treatment they had in terms of yield increasing was when legumes are rotated with a mixture of lupin and vetch.
Depth matters
The conversation also highlighted the importance of where carbon is stored in the soil profile.
“Carbon in roots does seem to decompose more slowly and stabilises and transform into soil organic matter more effectively than above ground biomass,” Professor Bell acknowledged.
He linked this directly to management choices that increase biomass: “If you can grow bigger crops, which means more biomass, you’re also growing more roots into the soil.”
On incorporation methods, he explained that different machinery targets different depths, including mixing up to 40 centimetres at one site and mole boarding, which is getting down to 30 centimetres, at another.
However, combining practices did not necessarily multiply benefits. “You get a benefit from the deep tillage... a benefit from the compost... but when you add them together, you don’t get anything extra.”
A practical message from the discussion was the importance of understanding constraints before investing in change.
“It’s always to me about looking at what are the most likely limiting factors and what’s the best investments to alleviate those,” Professor Bell said.
He also emphasised deeper soil testing as part of that process. “Getting down at least to 30 centimetres and having soil test information down to 50 event 70 centimetres so that you’ve got a good understanding of the soil profile that you’re dealing with.”
Across the discussion, Professor Bell reinforced that improving soil carbon in Wheatbelt sands is highly site specific, with early trial results showing mixed yield responses. The discussion underscored that soil carbon outcomes depend on understanding individual soil systems and applying targeted interventions, with change occurring over long timeframes rather than within single seasons.
To listen to the full conversation, view all our podcasts here.
Learn more about Richard’s research:
Article – New farming methods to sequester soil carbon – Soil CRC
Presentation – Program 4 Featured Project 2025 – Modern farming methods for sequestering soil carbon
This episode has been supported by the Cooperative Research Centre for High Performance Soils (CRC).
Published eNews #414, May 2026