Sharing the farmhouse on weekends with a 21-year-old recent Ag Science graduate — who’s firmly convinced his old man knows nothing about politics, economics, or history — is hard enough. Especially when I’ve read more books on these subjects than he’s even walked past in the UWA library. It gets worse when we stray into soil science, when there is nothing he does not know despite him never having been seen with a text book in hand let alone reading one. But long-suffering readers will know I like to poke around in the worlds of carbon farming and climate change from time to time. So, without seeking the untapped wisdom of my son Thomas, I’ll once again argue that soil carbon farming in the WA Wheatbelt probably belongs in the fantasy section of the library, not the science shelves.
To back this up, I’ve spent the past month wading through WA trial reports, DPIRD fact sheets, GRDC summaries, and CSIRO’s mammoth soil carbon studies — not to mention cornering some of the sharper ag consultants in the state to get their take. All because I keep hearing how the white-shoe brigade of soil carbon spruikers is teaming up with oil and gas outfits to flog carbon credits and buy up Wheatbelt farms, all on the promise of “farming the most common element in the universe.”
There’s nothing wrong with chasing a new income stream. But signing your paddocks up to a 25- or even 100-year contract to build and maintain soil carbon — under the same hot, dry, drought-prone conditions we’ve always had (and are told will only get hotter and drier) — is something you’d want to be absolutely sure about. The more I dig into the science, the clearer it is that the rhetoric is miles ahead of the local data. And that’s dangerous ground.
The compost heap rule
Let’s start with some backyard logic, which lines up neatly with my year 10 grasp of chemistry and biology. Building soil carbon is a lot like running a compost heap. You pile on plant material — straw, veggie scraps — toss in some nitrogen via manure or lawn clippings, keep it moist, and let the microbes do their thing. They chew through the carbon and nitrogen, churn out microbial goo, and over time it turns into stable humus.
But stop feeding it, or let it dry out and bake in the sun, and it all comes to a halt. Worse, it starts breaking down what it’s already built, pumping CO₂ back out. That’s your backyard compost.
Now think about a Wheatbelt paddock. We might get a decent flush of plant growth through winter and spring if the rain plays nice. But come November, we’re left with bare soils sitting under 40°C, no living roots, and barely a drop of summer rain. The microbes either retreat or die off. Any gains in organic matter are fragile. Left to face a hot WA summer, they shrink.
If we went and dug up those old farm veggie patches beside the collapsed farmhouses scattered across the Wheatbelt — once rich with compost — and ran a soil carbon test, we’d likely find them alarmingly low. Same story with those old house paddocks we used to keep for rams and killers around the sheds. They might’ve sat at 2.5% carbon back in the day. Today, after decades of continuous cropping, you’d be lucky to find them at 1%.
A century of WA trials tells the same story
If we step away from middle school examples — not that today’s green-leaning teachers would say anything other than the Wheatbelt could turn into a peat bog if only farmers went “regenerative” — and look at the local long-term data, it’s a sobering picture.
Take Merredin. A long-term trial there looked at stubble management over 17 years Hoyle (2006). Researchers compared plots where stubble was burnt against those where it was retained, tracking impacts on soil carbon. The result? No significant change in total organic carbon between the treatments. Both hovered around that familiar 1%, despite decades of innovation — from superphosphate in the ‘50s and lupins in the ‘60s to minimum till in the ‘80s and stubble retention in the ‘90s. About the only bright spot was that microbial biomass carbon did creep up, from roughly 100 to 150 kg C/ha, suggesting the bugs were a bit happier, even if the total carbon wasn’t.
It’s the same story elsewhere, like at Wongan Hills where DPIRD and GRDC have run trials for decades. You might see minor seasonal lifts, but over time it stabilises — not because it’s building, but because the system has found a fragile balance. A run of hot, dry years and it slides backwards; a couple of kind seasons with some legumes and maybe you’ll hit 2% again.
If we graphed it, it’d be a curve that drops from the original native level, then bumps along a flat line. That alone ought to give some pause to the carbon farming optimism doing the rounds.
What about all the talk from over east?
So it’s not just our local data throwing cold water on the hype — national studies back it up too. A lot of the big promises you hear come out of programs run over east. The CSIRO’s National Soil Carbon Research Program (2009–2013) is the big one. They sampled more than 2200 paddocks across Australia, including hundreds here in WA.
Lead scientist Jeff Baldock found that of all the systems they looked at, continuous cropping in rainfall zones under 450 mm was the least likely to build soil carbon. It didn’t matter how carefully you managed stubbles or how clever your rotations were.
To lift soil carbon by even 0.5% over 20 years, you generally needed either permanent pastures in areas with more than 600 mm of rainfall, or to cart in hefty loads of manure or compost. Which, let’s be honest, doesn’t pencil out for broadacre at scale.
The nitrogen handbrake
Then there’s nitrogen — the bit most carbon spruikers glide straight past.
Building stable soil carbon isn’t just about piling on more straw or roots. Your microbes need nitrogen to turn that carbon into humus. The old rule of thumb is roughly 24 parts carbon to 1 part nitrogen. If there’s not enough N in the system, the bugs can’t stabilise it. Or worse, they’ll start robbing nitrogen from your soil, which knocks your next crop.
The GRDC “Focus Paddock” project, which ran from 2014 to 2020 around places like Hyden and Yelbeni, showed this clearly. Even with more biomass going back into the soil, if there wasn’t enough nitrogen to support it, carbon levels didn’t reliably rise. In drier years, they actually went backwards.
Why our hot, dry summers kill the dream
You can get away with a lot more in Victoria or NSW. Their soils generally have more clay, which locks up carbon inside aggregates, and they often pick up summer storms that keep the microbes ticking over.
Here? Most of us farm loams or sandy soils, low in clay and natural fertility. Once harvest is done, we’re left with months of blazing heat. That’s when microbes either shut down or start burning through whatever organic carbon is there just to stay alive — releasing it as CO₂.
Look at the soil temperature and moisture graphs from Corrigin. Over summer, the top 10 cm hits 45°C, with moisture close to zero. That’s no place to build stable humus.
The Kimberley is a distraction
Every now and then someone pipes up about how the Ord has soils with 3% carbon, or how they’re seeing big gains under irrigation. Of course they are — they’ve got monsoonal summer rains, deep cracking clays, and cropping systems that keep the soil moist and full of roots year-round.
Try pulling that off at Kulin or Kondinin with five months of bone-dry summer, and see how far you get.
The only real bright spot in WA? The south coast. Where it might actually work
If there’s anywhere in WA where building soil carbon might genuinely stack up long-term, it’s along the south coast — around Albany, Esperance and Denmark. They get 550–650 mm of rainfall, the occasional summer shower, and often run permanent pasture systems. CSIRO and DPIRD trials down there show organic carbon lifting by about 0.2 to 0.4% over a decade.
But switch to a straight annual crop rotation, even in those higher-rainfall zones, and it largely stalls again. It’s the perennial pastures doing the heavy lifting — and that’s not how most of the Wheatbelt is set up.
The gaps in the research (and why DPIRD should step up)
One fair criticism of our state approach is that we simply haven’t run enough local, long-term trials. We’re missing hard data on things like multi-species cover crops, heavy legume phases, or deliberately feeding systems extra nitrogen to see what that actually does for stable carbon.
We also badly need work on the permanence question — what happens to soil carbon across WA’s brutal 15- to 30-year climate swings? Sure, you might build it up over a few wet years, but how much do you lose when the next run of decile 1 seasons hits?
That’s exactly the sort of trial DPIRD, GRDC and CSIRO ought to be running before more growers lock themselves into multi-decade contracts with clawback clauses waiting when carbon inevitably drops.
Two cautionary local tales
Look at the GRDC–DPIRD work around Hyden and Yelbeni in the <350 mm rainfall zone. Over eight years, they trialled legume-heavy rotations, retained stubble, managed grazing conservatively — and even when more biomass went back into the soil, there was no statistically significant rise in soil carbon. In fact, drier years often sent it backwards. Seasonal rainfall still called the shots, not the rotations or residue.
Then cross over to Walpeup in Victoria’s Mallee — another low-rainfall, light-soil system. Despite careful rotations and tillage, long-term data there shows soil carbon and nitrogen stocks actually declined compared to higher rainfall sites. The environment simply sets hard limits. Under many of today’s carbon contracts, even modest drops like these could’ve triggered penalties or repayments.
The international lesson
Another trial worth pulling into the conversation is the long-running Rothamsted experiments in the UK, which started back in 1843 — long before superphosphate or synthetic nitrogen. They’re still the world’s longest continuous ag trials, set on deep, fertile soils in the mild, wet climate of Hertfordshire. You’d think it was Eden for soil carbon.
Yet the numbers tell a sobering story. On plots that received a massive 35 t/ha of farmyard manure every single year, soil organic carbon roughly doubled in the first 50–60 years, climbing from about 1.2% to 2.4% in the top 23 cm. Over the next century, it only crept up a fraction more, to around 2.5–2.7%, effectively plateauing. That’s an increase of roughly 100–125% on the starting point — but most of it was front-loaded, with diminishing returns kicking in after just a few decades.
Meanwhile, plots treated only with mineral fertilisers (NPK) saw no sustained rise at all. In some cases, SOC even edged down. It all drives home the point that soil carbon sequestration has a biological saturation limit. Even under near-perfect conditions — fertile soils, lush biomass, steady rainfall and continuous heavy organic inputs — you eventually run out of headroom.
If that doesn’t rattle the carbon crusaders, I’m not sure what will.
If that sounds like just an academic exercise, look closer to home. To offset the CO₂ released from applying half a tonne of lime per hectare each year, you’d need to sequester roughly 60 kg of carbon per hectare annually. In WA’s 350 mm rainfall Wheatbelt, that’s a near impossibility. Long-term trials across the region show typical gains under conservation farming often come in well below 30 kg C/ha/year — with many seasons actually going backwards when drought knocks biomass around.
Unlike the Rothamsted plots in lush Hertfordshire, we simply don’t grow enough surplus biomass to drive that kind of sustained carbon build-up. In our fragile, low-input systems, trying to offset lime with soil carbon is chasing shadows. It’s yet another reason carbon farming tends to look far more appealing on a PowerPoint slide than in a farm budget.
Across the whole WA Wheatbelt, soil acidity is the other monster lurking just below the surface. That map of pH gaps tells the story: vast areas are sitting 50–100% below the target 0–10 cm pH, meaning we’re under-liming by an estimated 1 to 2 million tonnes each year. Acid soils don’t just hammer root growth and lock up nutrients — they also reduce the soil’s capacity to hold carbon.
So we end up stuck in a frustrating round robin: needing more lime just to keep pH up for crops and microbes, which drives up our carbon footprint, yet without enough lime, we can’t realistically store more carbon in the soil anyway. It’s the ultimate irony for the carbon credit crowd — chasing sequestration targets while ignoring the basic soil chemistry that underpins the whole system.
Most farmers I talk to already know that building soil carbon is a hard slog in our part of the world. But the climate change religion is still in full fever mode, and any heretic who dares question it risks being marched off to the pyre. I reckon I’ve racked up a monstrous carbon bill myself, just from all the times I’ve been burned at the stake for saying it like it is.
What really worries me isn’t the farmers — it’s the corporates. They’re desperate to find offsets because under Australia’s Climate Change Act 2022 (Cth) and the Safeguard Mechanism reforms (tightened again in 2023), the country’s top ~200 industrial facilities — those “designated large emitters” — are legally bound to reduce emissions intensity each year or buy carbon credits (ACCUs) to cover the gap. The safeguard baseline tightening climbs from about 4.9% a year now to 6% by 2030, and that carbon bill is only going to grow. So they’ll keep scouring the countryside for credits — even if the underlying Wheatbelt soil science doesn’t actually stack up.
In the end…
There’s a very good reason you don’t see many of WA’s sharp operators — the ones who keep buying land — rushing to slap 25-year caveats on their farms just to help oil and gas corporates meet obligations under the Climate Change Act and Safeguard Mechanism. When their agronomists run the numbers — factoring in lime, fert and fuel carbon bills, then modelling the risk of copping a carbon tax on a bumper year (thanks to the Tier 3 thresholds baked into federal law) — they’re horrified.
Anyone selling carbon credits off-farm in the medium to low rainfall Wheatbelt today would be mad with what we know. And for those still desperate to prove me wrong, I’m more than happy to publish the photos of the old farmhouse sites and the soil carbon tests on the long-forgotten veggie patch or long-drop dunny spot, benchmarked against the paddock on the other side of the house. I’d bet the numbers are about the same.
By all means, keep building organic matter — it’s good for your soil health, water holding and yields. But if someone wants to lock your paddocks up for 25 years on promises that read like they were trialled on a Margaret River dairy paddock, think twice. Even better get them to underwrite a guarantee that they will cover any losses if you fail to sequester the amount you sign up for.
Now Thomas, when he reads this, will no doubt roll his eyes at my attempt to play the science educator — because to him it’s all so blindingly obvious: as he keeps telling me… just look at the trial data, no point selling carbon credits when you should be buying lime.
But what he doesn’t fully appreciate yet is the sheer cunning of the snake oil salesmen who roll through the bush every decade with a fresh pitch. Each time, it’s another bright idea to help asset-rich farmers become asset-poor with a large cut to them: from co-operative farming schemes to llamas, mallees, managed investment funds, unit trusts, sandalwood, organic, jojoba, biodynamic, regenerative — and now, the latest carbon farming.
