Creating Unprecedented Increases in Soil Organic Carbon


June 2021

An Australian Soil Management compost trial at Temora has created ‘unprecedented’ increases in soil organic carbon.

Jason and Caroline Willis have been transitioning to a biological cropping system with minimal synthetic inputs since purchasing their property at Dirnaseer, which they’ve named ‘Heaven.’

“The increase in soil organic carbon in the first seven months is unprecedented as far as we can find from published research,” Jason says. “I believe this has some correlation with how we’ve been stimulating the biology in our soils.”

Jason says to fully understand what’s going on in the paddock, the trial would need to continue for longer.

“In the latter half of the two-year trial organic matter stabilised and with only two years of results it’s difficult to draw conclusions. More time is needed to fully understand what the manure is doing to our soils.”

They haven’t applied manure on the trial site this year and are monitoring changes from the initial applications.

“We’re keeping a close eye on it, changes will take time and don’t happen overnight.”

When Jason was a feedlot farm overseer between 1992 and 1997, he experienced first-hand the transformation of unproductive sodic soils on flood irrigation into wetting-self-mulching soils after applying compost.

More than two decades later he jumped at the opportunity to test how compost could increase soil organic carbon on their mixed farm of cropping and sheep. They are one of five properties trialling compost for Australian Soil Management through an active carbon farming grant.

“Everything is always interrelated and we see compost as another tool in our toolbox to improve our soils and therefore our production and bottom line.”

Their system has been biological since 2004 and although they do use some synthetic inputs and conventional farming methods, they are transitioning to a no-till, soil biology-focussed system.

They chose their second-worst performing paddock for the compost project to see how it would impact on the paddock’s poor soil nutrition. They were also testing the importance of calcium in their system plus looking for synergies with soil biology.

The compost resulted in improvements in the treated topsoil, which became darker with better aggregate structure. The compost also at least doubled the available phosphorus (P) to what Jason describes as ‘ideal levels and higher.

For the second year of the project, they planted a multi-species cover crop of summer and winter grasses plus summer and winter broadleaf in April 2020. The crop showed ‘outstanding’ growth. They also experienced yield increases in barley in 2019.

What excites Jason more than yield increases is seeing soil improvements.

“Rather than the compost only acting as a soil stimulant, I was expecting more of a soil structure change, which is exactly what’s happening. I love seeing the difference in the soil structure.”

For the past three years, soils tests across the farm have been showing potassium levels increasing to higher than desired levels, with the only exception being the most recent compost trial results.

Jason is perplexed at this unexpected result and is keen to know more.

“I would have thought the compost site, where we added eight tonnes of compost per hectare last year, would have had an even higher level of potassium. The soils were already showing elevated potassium levels, we applied more potassium, yet the percentage of K went down from 9.50 to 8.33,” Jason says.

“Is there going to be a massive release in years to come, or is there some interaction in the soil that is complexing the potassium?

“I really want to understand the changes in potassium from the compost, as well as changes in organic matter. This is something I will continue monitoring.”

Around the time they started the compost project, Jason and Caroline had come to the realisation the answers to the questions they were asking about their farming system were ‘holistic’.

“We have discovered that you need to look after your biology, chemistry and soil structure. All three are just as critical as each other. You can’t just focus on one area – you need to focus on balancing all three.”

They follow the mantra ‘feed the soil to feed the plant’ as part of what they believe is their duty of care as farmers to provide the most nutritionally dense food possible.

“Everything people eat comes from a farm; everything gets grown on a farm. We fervently believe it’s our responsibility as farmers to get this right.”

They are aiming for nutritionally balanced, healthy biological soils so they can grow nutrient-packed chemical-free produce.

“This goes back to farming’s duty of care – we should all be striving to produce the healthiest food we can for humans to eat.”

The ASM Active Carbon Farming Project is a Waste Less Recycle More initiative funded by a 'NSW EPA Organics Market Development Grant'

ASM has produced a new set of guidelines for farmers who want to build their soil quality and soil carbon stocks. If you would like a free copy, please send me an email at