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EMILY KWONG, BYLINE: You’re listening to SHORT WAVE from NPR.
AARON SCOTT, HOST:
I have to admit, I tend to take dirt a little bit for granted. It’s something I think about mostly if I track it in on the rug or if I need to wash it off the dog after we’ve gone for a hike. So in honor of World Soil Day, I am here in the backyard digging in the dirt.
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SCOTT: And this handful of soil that I just shoveled up, you know, at first glance, it looks exactly like what you’d think. It’s brown and crumbly. It’s got some clay consistency because it just rained. But as I start to break it apart and look closer, I see all sorts of things. There are earthworms. There are little white bug eggs, like caviar. There’s, you know, rotting little chunks of wood and then just this web of roots and fungi all twisted together.
ASMERET ASEFAW BERHE: If you put, you know, a handful of healthy soil – say, a forest topsoil, if you will, undisturbed – on the pam of your hands and look at it, just think about how that amount of soil holds, you know, up to 10 billion individual living things in it.
SCOTT: Wow.
BERHE: And those 10 billion individual things can come from anywhere up to five, maybe even more, thousand different species. So we’re talking about not just a lot of life, but a lot of diversity of life.
SCOTT: This is Asmeret Asefaw Berhe, a professor at the University of California, Merced. She’s also currently serving as the director of the Office of Science at the Department of Energy. But her first love is that earthy stuff beneath our feet. Just don’t call it dirt.
BERHE: As a soil scientist, I don’t like the D word. I think calling soil…
SCOTT: The D word (laughter).
BERHE: Yeah, that D word is not helpful because it assumes that this is a abundant resource that we can take for granted.
SCOTT: Asmeret says what makes soils special is all that biodiversity. It’s more than you’ll find in rainforests or coral reefs.
BERHE:And imagine, then, that all that diversity means that there is incredible power of that biological system to transform the environment.
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SCOTT: That involves decomposing dead things into nutrients to feed the next generations.
BERHE: What stands between life and lifelessness in our planet Earth is this thin layer of soil that exists on the Earth’s surface. And it’s the reason why we have the abundance and diversity of life that Earth is able to support, of course, the reason why we’re all able to eat because, you know, above 95% of all the food that human communities consume is either directly growing on soil or it’s animals that fed on those plants.
SCOTT: But while people have spent centuries maximizing how much we can grow from the soil, it’s really only in recent decades that we’ve realized that soil also plays a huge role in storing carbon and regulating the planet’s climate.
BERHE: Allowing plants to grow means plants can take out CO2 from the atmosphere.Because soil has these minerals, they’re able to lock in the carbon in almost like a soil bank kind of situation.
SCOTT: The total amount of carbon stored in soil is more than three times the carbon in the atmosphere. And every day, humans release a chunk of that carbon through all the things we do to grow crops and livestock, things like cutting down forests, tilling soil with machines, and planting year after year without giving fields time to recover. According to the U.N., about a third of the world’s soil is now degraded.
BERHE: Especially if it’s physically disturbed by tillage and other activities and a rainstorm moves through, you know, a significant amount of soil can be eroded within days, you know, if not shorter. But it takes close to a thousand years to be able to produce an inch of soil.
SCOTT: Wow.
BERHE: That’s how precious this resource is.
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SCOTT: Today on the show, for World Soil Day, we revisit our conversation with Asmeret Asefaw Berhe andplay in the D-I-R-T, exploring all the ways healthy soil makes for a healthy world. I’m Aaron Scott, and this is SHORT WAVE, the science podcast from NPR.
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SCOTT: Asmeret, can you start out by giving us a sense of how much carbon is stored in the soil around the world, and then the role that that is playing in climate change?
BERHE: Yeah. So there’s – interestingly, we don’t actually know exactly how much carbon is in soil. Part of it is because of the diversity of soil types and ecosystems. But we have a very good estimate of what it’s likely to be, and it’s likely to be on the order of about 3,000 billion metric tons of carbon.
SCOTT: Which sounds like a lot (laughter).
BERHE: It’s a lot. It’s a lot more than the amount of carbon you have in all of the world’s vegetation, all the atmosphere – actually, putting them together and twice over.
SCOTT: Wow, OK.
BERHE: Yeah, so it’s a lot of carbon. But historically what has happened is the amount of carbon that hs been coming into soil from – via photosynthesis primarily has not really changed significantly, but the rate at which carbon has been leaving the soil system has been increasing. And that’s because of the disturbance with intensive cultivation systems that I mentioned earlier. And so in the last 12,000 years or so that human communities have been engaged in agriculture, the estimate is that about 120 billion metric tons of carbon that was in soil – just in the top 2 meters of soil – has been released to the atmosphere. In particular, the fastest rate of loss happening since the Industrial Revolution.
So a lot of carbon that was in soil has been released to the atmosphere already, and we run a risk of hundreds of billion metric tons of carbon being released to the atmosphere if we don’t do something about global warming in the next couple of decades or so, ’cause remember that a lot of the carbon that exists in soil, it exists near the poles in arctic environments and areas that havebeen covered by ice for long periods of time. And the thawing and the draining of the permafrost means that carbon that had been trapped in that ice for long periods of time is now going to be oxidized, making this problem that we have even worse.
SCOTT: So as we think of ways to address the carbon in the atmosphere, I mean, there’s – it’s very popular, the idea of plant more trees, they’ll suck up the carbon. Can you talk about some of the solutions there are for the soil of how we go about addressing its degradation and increasing the amount of carbon that it can be pulling out of the atmosphere?
BERHE: Yeah. So planting more trees is a good idea from many parts of the world, partly also because that would allow you to replant deforested land. And if we could do that, you know, it’s responsive. Obviously, as the plants grow, they will take up CO2 from the atmosphere, and part of that carbon will make its way into soil and be stored in soil. So it’s a win-win for that perspective.
ut that’s not the only mechanism that we have at our disposal. First, we can minimize the disturbances that the soil system is experiencing from things like tillage by reducing the excess amount of agricultural chemicals that are added, by bringing back residues and other sources of, you know, organic matter, like waste products, back into the soil whenever it’s possible, so that…
SCOTT: So…
BERHE: …The nutrients…
SCOTT: …Compost.
BERHE: …Make their way past – compost and things like that. So all of that can make a huge difference. It’s important, though, to remember that there is a variety of options out there, and they’re appropriate for different types of environments. So, for example, a big part of the world is savannas and grasslands, and grasslands themselves are actually extremely effective in carbon sequestration in soil in particular. So I wouldn’t be advocating, for example, to put back trees where the ecosystem conditions dictate that this is more favorable fr grasslands.
SCOTT: And, I mean, because grasslands can have roots that are 10 feet deep…
BERHE: Exactly.
SCOTT: …And are storing all that carbon underground in a place where it can’t be burnt up.
BERHE: Exactly.
SCOTT: Are there things we could be adding to the soil or maybe ways we could be planting differently or even engineering our plants so that we’re actually pulling more CO2 out of the atmosphere and depositing it in the soil? For example, I know that you’ve been looking at things like adding biochar to the soil, basically a charcoal made from burnt plant material.
BERHE: Yeah. No. There’s a whole bunch of options out there. Some of it includes biochar, which had been shown to allow better water and nutrient retention in soil, meaning favorable plant productivity and carbon sequestration. There’s also efforts to put back deep-rooted perennial grasses, for example, which, as you said, not just put a large amount of carbon in soil, but do so at deep soil layers where i’s likely to persist for long periods of time. There are efforts for genetically modifying plants in one way or another so that they can have extensive, deeper rooting kind of components that then allow them to contribute to carbon sequestration. There are a number of things we should be doing with the waste products, including municipal waste, I think is a really important component.
SCOTT: Which is to say human waste, right?
BERHE: Human waste, animal waste, so just waste derived from living things, basically. All of that has an important role to play in bringing back the residue, the nutrients, the carbon that could help with rehabilitating soil and making it even more capable of sequestering atmospheric carbon dioxide. So there’s a number of these efforts. The important ones in terms of the fast rate of magnitude for carbon sequestration, for example, are putting back wetlands and mangroves because they have a very high rate of carbon sequestration. So there’s a number of these eforts that we could do that are appropriate for a variety of environmental settings.
SCOTT: We humans are facing a lot of crises on this earth, but Asmeret says we can’t tackle them separately. Just like that soil in my backyard was an integrated ecosystem, our atmosphere and our soils and our oceans, they’re all connected too. And the good news is that means the solutions to our crises are also interconnected. We just need to dig in and get our hands a little dirty – or soily. Happy World Soil Day, SHORT WAVErs.
This episode was produced by Rebecca Ramirez, edited by Gabriel Spitzer and fact-checked by Abe Levine and Margaret Cirino. Beth Donovan is our programming senior director, and Anya Grundmann is our senior vice president of programming. I’m Aaron Scott. Thanks for listening to SHORT WAVE from NPR.
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