Soil and soil health might not sound exciting, but it's fundamental to a habitable world.
In fact, it's home to a staggering 56 percent of all life on earth.
And this thin layer of soil that covers the earth’s surface represents the difference between survival and extinction for most terrestrial life.
Rain falling on that thin little layer – often just a few inches thick – provides us with 95 percent of our food – say the United Nations.
Soil is a living entity and it acts as the planet’s ultimate digestive system.
It decomposes everything that ever lived – plants, animals, even us – and then recycles it to enable new life. Which makes it the only site in the universe where death is resurrected into life.
This living planetary “skin” is proportionally 10,000 times thinner than our own. And we need to constantly remind ourselves how fragile it is. How much we rely on it. And care for it accordingly.
Because the health of soil, plants, animals, people and the environment is one.
And indivisible.
What is soil and how is it made?
Soil's mostly just crushed up rock, water and air – but it’s only when you add a magic ingredient that things can grow in it. That magic ingredient is called soil organic matter.
Here's the recipe for soil.
Take:
- 50% minerals - in the form of crushed up rock
- 10% organic matter (ie. what's left over after plants and animals decompose, plus plenty of microbes)
- 25% water
- 15% air
Make sure that when you mix it there's at least 50 percent pore space. Half the pore space should contain water and the other half air. A bit like a soggy cake.
And that's it.
It's basically a mix of physical, chemical and biological elements. Minerals from rocks, organic matter from dead plants and animals, some living organisms. And, of course, air and water.
And that's what keeps us all alive.
Simple, isn't it.
The top six inches of soil are the most important of all
The micro-thin ribbon of soil that feeds us is called Topsoil.
It's just the top six inches, or so, of soil. The bit we walk on. But it's where almost all of the planet’s biological soil activity takes place.
Most of the ingredients for new topsoil come from the atmosphere – carbon, hydrogen, oxygen and nitrogen – either directly or via plants and animals.
Together they form the bulk of what's called “soil organic matter”. Think of it as compost. A mix of microorganisms, dead animals and plants. Basically, anything with carbon in it – either living or dead.
And that's when the magic happens.
The interaction between organic matter, fungus and billions of microbes turns crushed rock, air and water into topsoil. And it’s this that provides plants with the water and minerals they need.
And us with food.
It all happens because plants and microbes in the soil form a partnership and swap stuff between each other.
Soil microbes supply plants with almost all the nutrients they need to grow (like minerals). In exchange for these nutrients, plants supply microbes with the carbon they need to build new cells.
It’s a sort of swap-shop.
And it’s called the microbial bridge. If that bridge collapses carbon stops flowing to the soil.
That's important, because – when it comes to climate change – carbon in the atmosphere is only part of the equation. Poor soil health plays a big role too.
Because unhealthy soil doesn't just stop storing carbon. It begins to release stored carbon back into the air. Lots and lots of it.
A hidden army of microbes put carbon into the soil
Good healthy soil is home to an incredible, secret, universe.
Everything from tiny single-cell organisms like bacteria and protozoa, to fungi, insects, invertebrates... even animals, like moles.
But it's the tiny stuff like bacteria that perform the biggest role. They break down organic matter, deal with toxins and pathogens, and recycle nutrients to the plants above ground.
And, importantly for us, they help to store carbon.
Just like the human gut, soil relies on a thriving community of healthy bacteria, fungi and microbes to stay healthy and balanced.
So, as a general rule, the more organic matter in soil, the healthier it is. The more life it can support. And the more carbon it can store.
Carbon stored in the soil can remain there for centuries, or more.
In fact, UK soils store the equivalent of 70 years worth of our annual greenhouse gas emissions.
But even healthy soil can't carry on absorbing carbon for ever.
Eventually things reach a state equilibrium – where carbon flow in equals carbon flow out. The soil simply can’t take in more carbon.
So, when it comes to climate change, the big gains are to be made in degraded soils. These are the soils that have lost lots of carbon – which means there's room to put carbon back in.
Degraded soil loses carbon first. Then it just blows or washes away
The decline of pasture and the rise of intensive arable cropping has mined nutrients from the soil, and left bare earth exposed and vulnerable to weather.
More importantly, it's stripped out organic matter – and carbon – from the soil.
The result is, a quarter of the world's agricultural land has been degraded by agriculture. So too, is almost 40% of the UK's arable land.
And globally, over the past century between 42 – 78 billion tonnes of carbon have been lost from degraded soils.
Degraded soil is also far more prone to erosion. Because without organic matter soils lose the glue that stops smaller particles from being blown away or washed into our rivers.
Ploughing a field typically erodes soil 10 to 100 times faster than it takes to create. First it lets carbon escape from the soil and into the atmosphere. And, eventually, the topsoil is lost.
In fact land without vegetation can be eroded more than 100 times faster than land with vegetation on it.
In farming the best ways to destroy the soil – and the environment – are these:
- Disturb it repeatedly – it loses organic matter and carbon
- Compact it – it interferes with microorganisms
- Add chemical fertilisers – it acidifies the soil
- Smother it with toxic agrichemicals – especially fungicides
Which, more or less, describes exactly how we farm today.
In the UK three quarters of sediment pollution comes from farming. Soil that's been washed out of the fields and into the rivers.
And in the south west of England, it's estimated, up to half of river sediment comes from maize fields alone.
Globally the picture's just as bad. If not worse.
Based on figures provided by the European Commission Joint Research Centre – the planet lost approximately 26 tons of topsoil for every living human in just the four years running up to 2017.
And that's not only a lot of soil. It's a lot of carbon too.
"Where would I go and what would I do? I know what the land did once for me, maybe it will do it again." Texas Farmer living in American Dust Bowl of the 1930's
We need to move on
Regenerative farmers seek to protect and rebuild soil
Land and soil degradation are the hidden cause of many of our most urgent problems.
So – for farmers who farm in a carbon friendly way – the goal is to keep the soil healthy. Which, as a consequence, keeps carbon locked in.
Or, they aim to restore degraded soil, which leads to healthy soil and more carbon stored. That process starts with improving soil health and building up organic matter.
One way to do that is to graze animals on it.
Because evidence suggests that good grazing management helps to maintain carbon stocks. While over grazed or under grazed land degrades the soil. And releases carbon.
If we're able to restore land that's been degraded then there's room to sequester a lot more carbon.
It's not a “cure for climate change”. But it certainly helps.
We’re left with one big question
Everyone knows the atmosphere's facing its highest levels of carbon in history.
But hardly anyone knows that underground the total opposite is taking place. Industrial agriculture has drained the soil of carbon.
Unfortunately, those losses have a permanent effect on carbon concentrations in the atmosphere.
And, going forward, even small changes in carbon released from the soil will have a significant effect on atmospheric CO2.
Grassland is not, in itself, a carbon sink. Once it's reached equilibrium it becomes a carbon store. Neither gaining or losing.
Whereas degraded grassland is a potential carbon sink – that is, until it gets to equilibrium.
But unless we can store, or sequester carbon somewhere, it'll be almost impossible to meet our targets for climate change.
So we've two choices to make.
Do we restore degraded soil, so that it sequesters more carbon? This'll take anything up to 70 years and the gains will slow over time.
Or, do we put our efforts into protecting the large stocks of grassland carbon we've already got. Because soils lose carbon much quicker than they gain it,
The biggest question of all is... can we do both?
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