How soil can heal the world

Don’t blame cows — the solution to reducing methane and carbon levels lies under our feet.


The Weekend Australian Magazine, June 26, 2021

Matthew Evans on his farm in Tasmania’s Huon Valley

Outside my office window lies a paddock fringed with silver wattle bursting forth in millions of golden blossoms. Behind the silver wattle, a pioneer species, lies a forest of stringybark and peppermint eucalypts, which once ­dominated this landscape. It’s early spring and a warm wind is gusting up the gully. The grass has turned emerald green in the paddock, overshadowed by wisps of brown. The thin stalks left over from last year billow like a bald man’s comb-over.

If we stopped farming, this land would ­probably revert to eucalypt forest. But not the same forest, because that was managed land – the original inhabitants, the Melukerdee people, burned in a patchwork pattern to create open woodland. They altered this land to feed themselves.

We alter it, too, and grapple with the sometimes-competing needs: to look after the soil and still produce nutritious foods. Looking after soil, we think, can include grazing animals – which for many is controversial these days. If there’s one area in which the battle for the food dollar has met the battle for the climate head-on, it’s meat. Those who believe we should all abstain from ­eating meat have found the ultimate enemy – ruminants, livestock whose digestive systems ­produce methane, a potent greenhouse gas.

The best thing you can do for the ­environment is to stop eating meat, according to Joseph Poore, co-author of a scientific paper titled Reducing Food’s Environmental Impacts Through ­Producers and Consumers, which was published in Sciencemagazine in 2018. On the release of his paper, Poore came up with a misleading – and unfortunately often repeated – statement: “A vegan diet is probably the single biggest way to reduce your impact on planet Earth, not just greenhouse gases, but global acidification, eutrophication, land use and water use. It is far bigger than cutting down on your flights or buying an electric car.” That quote made headlines around the world and has been used to energise plant-based food proponents.

Problem was, Poore’s paper did not look at ­anything other than food. Not coal. Not fugitive emissions from fracking or natural gas extraction. Not petrol, or the embedded energy in steel or concrete. It didn’t look at what’s possible in soil. It also used a fairly arbitrary carbon life-­cycle accounting ­system that allows for ­emissions from livestock, but not carbon cycling in pasture, and in the earth that grows it. ­Emissions, but not capture.

Nevertheless, his message set the anti-livestock movement in motion. Finally, their cause wasn’t just about the exploitation of animals, or about selflessly giving up what has long been for many a dietary staple. It was about saving the world.

Don’t blame us: grazing land is good for methane reduction

Methane gets a bad rap in the climate change stakes. Not surprising, really, given it has a more powerful warming effect than carbon dioxide. Until recently, methane was estimated to be about 28 times more warming over 100 years than carbon dioxide, based on theoretical models (ones Poore had been using). But that figure has been revised down to eight times more warming by looking at actual results more closely. Still, eight times worse is eight times worse; it’s just less bad.

For a long time, as cows and other ruminants emitted methane, mostly through burping, and wetlands and rice paddies emitted methane from soil, there was a natural harmony. That’s because there are things called methanotrophs living in soil – microbes that digest methane and use it for energy. They have so far eluded most efforts at ­cultivation in the lab, but they can thrive in the earth. In healthy soil. A thing that can help moderate the climate effects of methane lives in soil!

(they started outcompeting other herbivores 20 million years ago), so the soil biome and the ruminants have co-evolved. It’s hardly surprising, then, that the microbes in the soil underneath where the cow is burping are busy converting that methane into more harmless components.

While it’s a hard area to research, and it’s very early days, it seems the methane-eating microbial colony expands when there is more methane directly above the soil, and a ruminant-grazed pasture can support more methane-eating microbes. Studies on methanotrophs have shown, consistently, that they exist in higher numbers in healthy soil, and that deeper soil has more methane eaters in it. But in places where soil is compromised, or where artificial fertiliser is used, the methanotrophs drop – not only in number, but also in diversity. In other words, if you want to get rid of methane, don’t use artificial fertilisers; use natural fertilisers and let soil health take priority.

Atmospheric methane has been increasing by 10 million tonnes a year, or about 1 per cent, on average, for the past 200 years. Much now comes from fracking for natural gas. Some comes from traditional drilling for oil and gas. Some comes from thawing tundra, melting ice sheets, coal mines, rubbish tips, sewage plants, slurry pits and drying peat bogs. Some comes from growing rice, of course, as does a proportion from ruminants.

It appears, however, that recent increases have nothing to do with the ruminant herd, or the rice paddies. Despite no real increase in the global ruminant herd between about 1990 and 2010, methane kept rising at the same rate it has since the Industrial Revolution. The culprit, as ever, is the burning of fossil fuels. At the same time, we’re destroying the only way we know to actively get rid of methane on Earth – soil microbes.

Soil microbes currently process up to 20 per cent of the methane that is produced, but they can only do that where the soil is healthy. And they could break down much more methane if land is fertilised using compost. Methane-eating microbes work far, far better if you let grazing animals poo on the grass that they graze, rather than locking the animals away in intensive farms and bringing in feed from elsewhere.

Evidence from 2020 shows light grazing can increase the methane-digesting ability of methanotrophs by more than four times, compared to ungrazed grasses. It’s also now known that increasing levels of soil carbon usually increases the ­number of methane-consuming microbes the land contains. In contrast, ploughing land diminishes the ability of that piece of earth to absorb ­methane. In other words, grazing land is good for methane reduction. Cropping land isn’t, unless it’s no-till: research has estimated that no-till agriculture can help break down methane up to 11 times faster than ploughed land. Soils under rotational grazing systems work even better at removing methane than no-till cropping. Rotational grazing also emits less methane and nitrous oxide.

Can soil methanotrophs under a single grazed paddock actually neutralise the methane emitted from the animals chewing their cud after eating the grass that grew on the same land? It’s unlikely, but they don’t need to – because it turns out that forests are usually better at metabolising methane than grasslands. So as long as we keep wooded areas near our grazing land, they will do a fair amount of the work, too.

The ability of soil to store carbon is one of the climate’s great hopes

Soil isn’t some innocent bystander in the climate change debate. It contains all the elements that make up the most important greenhouse gases: the carbon and hydrogen in methane; the carbon and oxygen in carbon dioxide; and the nitrogen and oxygen in another highly warming greenhouse gas, nitrous oxide. Soil can act as either a sink or a source of greenhouse gases. ­Perhaps surprisingly, the top one metre of the Earth’s crust has way more carbon in it than the air. Soil, with both the living and decomposing lives within it, contains 4.5 times more carbon than the rest of that biosphere put together – including all the plants and animals on Earth. All that carbon was, or still is, the result of living things. In other words, while we often view trees as a ­carbon sink – a way to store carbon that’s not in the atmosphere – it’s actually soil that is doing the heavy lifting.

In fact, according to David Montgomery, ­Professor of Earth and Space Sciences at the ­University of Washington, about a quarter to a third of all the new carbon added to the ­atmosphere since the Industrial Revolution has come from soil. As we’ve eroded, overgrazed, ­cultivated and impoverished soil, we’ve allowed lots and lots of carbon to be emitted into the air. If growing food hadn’t been so bad for soil, the increase in levels of atmospheric carbon since the Industrial Revolution would be about 35 per cent lower than we have today.

Farmland is still releasing soil carbon as I write. But some regrowth forests, and well-managed grazing lands, are helping soil to actually be a net sink of carbon. In a good news story, for the past two decades we’ve actually increased the amount of carbon stored in plants and soils by better ­managing some of our land. And the evidence is that we can sequester, or store, more carbon in soil than we thought, and more than we have been. Way more. In fact, the ability of soil to store carbon is one of the climate’s great hopes. According to former French agriculture minister Stephane Le Foll, it can be such a big carbon sink that it can heal the world.

Matthew Evans on his farm in Tasmania’s Huon Valley

In 2015, when the world’s leaders met to discuss a way to reduce climate change at the Paris Climate Summit, Le Foll touted a simple idea for helping pave the way (or should I say, garden our way) to planetary health. In French, it’s called 4 pour Mille (4 per 1000) – and it relates to a percentage increase in soil carbon. If the top 30-40cm of all the world’s agricultural soils, and soils under human management, were to increase in carbon by a tiny amount, by just 0.4 per cent a year (four parts in 1000), virtually the entire global increase in carbon emissions for each year could be offset. If we did this for a few years, while we transitioned out of fossil fuel use – the real culprit in the long term, and something that simply has to be addressed – we’d not only improve soil, we’d also be helping the climate.

An increase in soil carbon does other equally vital things. It allows the soil to store water better in dry times, and to drain better in heavy rains. It holds the soil together better. More carbon in soil means more methanotrophs, the microbes that digest methane. And, of course, more carbon means more of all the other subterranean life, which means more micronutrients for us if we eat those plants. It’s a win, win, win, win.

The 4 pour Mille agreement, initiated in France and signed by the majority of nations on Earth, acknowledged the power of agriculture. Where the focus on carbon sequestration (storage) has often been solely on trees, or large-scale carbon capture by humans at power plants (which is yet to be proven viable), 4 pour Milletalked about the massive sink we already control. We just have to use soil in the way it’s intended.

Storing carbon in soil was not on the public agenda in 2015 when Le Foll first mooted his scheme. Things have changed a lot since then. In 2020, fossil fuel giant BP announced it is working in the soil carbon space (probably, the uncharitable might argue, to offset its emissions). Bayer (the owner of Monsanto, most famous for its glyphosate herbicide Roundup) is paying farmers to store carbon in soil by promoting a system of spray and no-till, which isn’t completely ideal, but is at least a start. The Australian Government, even under a series of remarkably denialist ­leaders, has started paying farmers to store ­carbon in soil. Meanwhile, Ireland’s carbon accounting makes specific mention of the role of grasslands and their carbon-storing capacity in its response to the climate crisis.

The target set by 4 pour Mille is ambitious. You’d have to get every farmer and every land manager on the globe actively working to store carbon. Mono-cropping grain growers and vegetable producers would struggle to store carbon at that level. Many graziers might be hard-pushed to produce such results. Not everybody has to achieve the same level, but the average, across all human managed landscapes, is a big ask.

The 4 pour Mille movement points the way to a more secure food system. While it has powerful detractors, it also has powerful allies. Much work can be done in this space, with huge benefits to the environment.

Every little bit helps. The 4 pour Mille ­agreement relies on lots of small and large changes, on all human-managed landscapes, from the biggest corn farm to the smallest rose garden, recognising that tiny changes in how we tend our land can have a huge impact on the earth that nourishes us.

Edited extract from Soil – The Incredible Story of What Keeps the Earth, and Us, Healthy by Matthew Evans (Murdoch Books, $32.99).