Sharing a house with a 21?year?old Ag Science graduate is challenging enough. Especially when he’s convinced his old man knows nothing about politics, economics or history— despite the fact I’ve probably read more books on those subjects than he’s walked past in a library.

But where it really gets lively is when the dinner?table chat drifts to soil science and my lack of science credentials are on full display.

Long?suffering readers know I like to poke around in the world of agricultural science particularly anything to do with carbon farming and climate change, so — without drawing on the untapped wisdom of my son Thomas — I’m going to argue, once again, that soil carbon farming in the WA Wheatbelt belongs firmly in the fantasy section of the library, not the science shelves.

To test that theory, I’ve spent the past month knee?deep in WA trial reports, DPIRD fact sheets, GRDC summaries and CSIRO’s door?stop studies — and cornering a few of the sharper ag consultants for their views. Why? Because everywhere I turn I hear that the white?shoe brigade of carbon spruikers has teamed up with oil and gas outfits and are hard at work attempting to flog carbon credits and buy up Wheatbelt farms, all on the promise of “farming the most common element in the universe.”

Now while there’s nothing wrong with chasing an extra income stream, I have real concerns over signing farms over to 25? or even 100?year contracts 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)— which is a gamble you’d want to be very sure about. The deeper I dig into the science, the clearer it becomes that the rhetoric is miles ahead of the local data. And that’s dangerous ground.

Let’s start with some backyard logic — the sort that fits 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 — throw in some nitrogen from manure or lawn clippings, keep it moist, and let the microbes do their thing. They chew through the mix, churn out microbial goo, and, over time, it turns into stable humus.

But stop feeding it or let it dry out in the sun and everything stalls. Worse, the heap starts cannibalising itself, breaking down what’s already built and pumping CO? back into the air. That’s your backyard compost.

Now think about a Wheatbelt paddock. We might get a good flush of growth through winter and spring if the rain plays nice. By December, though, we’re left with bare soil under 40?degree heat, no living roots and barely a drop of summer rain. The microbes either retreat or die. Any gains in organic matter are fragile — left to face a WA summer, they shrink fast.

Dig up the old veggie patches beside the collapsed farmhouses scattered across the Wheatbelt — once rich with compost — and you’d likely find alarmingly low carbon levels. Same with those house paddocks we used to keep for draft horses, dairy cows, rams and killers. They might have sat at 2.5?per cent carbon back in the day. Today, after decades of cropping, you’d be lucky to find 1?per cent.

That little backyard experiment scales up neatly. Because when you swap the compost heap for a Wheatbelt paddock and look at the data, a century of WA trials tells the same story.

Take Merredin. A trial there tracked stubble management over 17 years (Hoyle, 2006), comparing plots where stubble was burnt with plots where it was retained. The result? No significant change in total organic carbon. Both treatments hovered around that familiar 1?per cent.
The only flicker of improvement was microbial biomass carbon, which crept from roughly 100 to 150?kg C/ha. The bugs were a little happier, even if the total carbon wasn’t.

It’s the same picture at Wongan Hills, where DPIRD and GRDC have run long?term trials for decades. You see seasonal lifts, but over time it just plateaus. A run of hot, dry years and it slides back; a couple of kind seasons with legumes and maybe you hit 2?per cent again.

Decades of innovation — superphosphate in the ’50s, lupins in the ’60s, minimum till in the ’80s, stubble retention in the ’90s, amelioration in the 2000s — made barely a dent.

Graph it and it’s a simple curve: native vegetation at the top, a drop when farming begins, and then a flat line. And that flat line should give pause to anyone buying into today’s carbon farming optimism.

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.

You can get away with a lot more in northern 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 duplex 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 CO?.

Look at the soil temperature and moisture graphs from the eastern Wheatbelt. Over summer, the top 10?cm hits 45?°C, with moisture close to zero. That’s no place to build stable humus.

It’s not just our local data pouring cold water on the hype — national studies back it up too. The CSIRO’s National Soil Carbon Research Program (2009–2013) is the big one. They sampled more than 2,200 paddocks across the country, including hundreds here in WA.

Lead scientist Jeff Baldock found that continuous cropping in rainfall zones under 450?mm was the least likely system 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 half a per cent over 20 years, you generally needed either permanent pastures in areas with more than 600?mm of rainfall, or huge amounts of imported manure or compost. It might work for the dairy farmers in Margaret River, but good luck making it work in Moora or Mullewa.

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?per cent 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.

Another trial worth pulling into the conversation is the long?running Rothamsted experiments in the UK, which started back in 1843. 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?per cent to 2.4?per cent. Over the next century, it only crept up a fraction more, to around 2.5–2.7?per cent, effectively plateauing. That’s an increase of roughly 100–125?per cent 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.

Now lets add some lime to the equation. To offset the CO? 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 over the long term, that’s a near impossibility. Even under even the most regenerative conservation farming system, they can barely keep up with the carbon they need to offset the lime they should be applying.

Unlike the Rothamsted plots in lush Hertfordshire, we simply don’t grow enough surplus biomass to drive the kind of sustained carbon build?up needed to offset our intensive operations. In our fragile, low?input systems, trying to offset not just lime but all our scope three emissions 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 has to be the monster that scares off farmers from selling their carbon credits. That map of the states pH problem tells the story: vast areas are sitting 50–100?per cent 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 and we are not applying anywhere near enough lime to address this problem.

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 that can’t be met with our hot drying climate.

Not that this is news to most farmers, as most of the ones 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 for burning. 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.

But 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, the country’s top ~200 industrial 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?per cent a year now to 6?per cent by 2030, and that carbon bill is only going to grow. So they’ll keep scouring the countryside for credits or farms to buy to turn back to trees — even if the underlying Wheatbelt soil science and rainfall for tree growth and carbon sequestration doesn’t actually stack up.

Layered over all this soil?carbon wish?casting is a new and equally dangerous distraction: Scope?3 emissions rules. Canberra is already flirting with pushing these accounting obligations down to the farm gate. That might sound harmless to an inner?city policy wonk, but in practice it’s a slow?acting poison for Australian agriculture.

Why? Because Scope?3 emissions are, by definition, indirect. They count everything upstream — the emissions from fertiliser factories, shipping, diesel refining — and everything downstream — processors, retailers, even the food miles on the truck to Coles. Farmers don’t control any of that. If you start forcing us to account for and offset everyone else’s emissions, you’re just piling costs onto the one sector that can’t pass them on.

Internationally, almost no agricultural exporters face Scope?3 burdens. So, if we go it alone, we’ll just push production offshore to less?regulated countries with higher emissions intensity. That’s carbon leakage 101 — global emissions go up, Australia’s farm sector goes down.

If policymakers really cared about net emissions and food security, they’d keep agriculture out of the Scope?3 trap, but we are locked into this mad economic suicide pact that few seem to understand.

There’s a very good reason you don’t see many of WA’s sharp farm 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, fertiliser 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 location of the old long?drop dunny, 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 a quarter of a century on promises by someone promising cash for carbon, think twice. Even better, ask them to provide you with a guarantee that they will cover any losses if you fail to sequester the amount you sign up for. So when Thomas finally reads this, he’ll roll his eyes at Dad trying to play at being an aggro and farm advisor. To him it’s all obvious: look at the trial data, look at your emissions, show the guy with white shoes the door, buy more lime, and keep any credits you can earn to shield yourself from the Scope?3 demands that the big end of town will soon dump on you.

He gets that part.

What he doesn’t yet fully appreciate is just how smooth the snake?oil salesmen are when they come through the bush with their next big idea. Every decade it’s something new: llamas, mallees, managed investment funds, sandalwood, jojoba, biodynamics — and now carbon farming. If history is any guide, the one thing they are good at is farming fools.