Short Wave - Don't Call It Dirt: The Science Of Soil

Episode Date: December 5, 2022

It's easy to overlook the soil beneath our feet, or to think of it as just dirt to be cleaned up. But soil wraps the world in an envelope of life: It grows our food, regulates our climate, and makes our planet habitable. "What stands between life and lifelessness on our planet Earth is this thin layer of soil that exists on the Earth's surface," says Asmeret Asefaw Berhe, a soil scientist at the University of California-Merced. Just ... don't call it dirt. "I don't like the D-word," Berhe says. Berhe says soil is precious, taking millennia to regenerate. And with about a third of the world's soil degraded, according to a UN estimate, it's also at risk. Prof. Berhe, who is also serving as Director of the U. S. Dept. of Energy's Office of Science, marks World Soil Day by telling Aaron Scott about the hidden majesty of soil and why it's crucial to tackling the climate crisis. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. 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's Soil Day, I'm here in the backyard digging in the dirt. In this handful of soil that I just shoveled up, you know, 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. If you put, you know, a handful of healthy soil, say a forest top soil, if you will, undisturbed on the palm of your hands and look at it, just think about how that amount of soil holds up to 10 billion individual living things in it. Wow. 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. This is Esmerit Asafau-Beah, 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. As a soil scientist, I don't like the D word. I think calling soil. That D-word is not helpful because it assumes that this is an abundant resource that we can take for granted.

Asmaret says what makes soil special is all that biodiversity. It's more than you'll find in rainforests or coral reefs. And imagine then that all that diversity means that there is incredible power of that biological system to transform the environment. That involves decomposing dead things into nutrients to feed the next generations. What stands between life and lifenessness 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, it's the reason why we're all able to eat.

Because, you know, above 95% of all the food that human communities consume, either directly growing on soil or it's animals that fed on those plants. 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. 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. 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 UN, about a third of the world's soil is now degraded. 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, even not shorter.

But it takes close to a thousand years to be able to produce an inch of soil. That's how precious this resource is. Today on the show, we're going to play in the DIRT and explore all the ways healthy soil makes for a healthy world. I'm Aaron Scott, and this is Shortwave, the Daily Science Podcasts from NPR. Asmodet, 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. Yeah, so 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. Which sounds like a lot. 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. Wow. Okay. Yeah, so it's a lot of carbon, but historically what has happened is the amount of carbon that has 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 two 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. Because remember that a lot of the carbon that exists in soil, it exists near the poles in Arctic environments and areas that have been 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. be oxidized, making this problem that we have even worse. So as we think of ways to address the carbon in the atmosphere, I mean, 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? 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, it's responsive, obviously, as the plants grow, they will take up CO2 from the atmosphere and part of that carbon will make it its way into soil and be stored in soil. So it's a win-win for that perspective. But that's not the only mechanism that we have at our disposal. First, we can minimize the disturbances that the soil system is experienced, from things like tillage, by reducing the excess amount of agricultural chemicals that are added,

by bringing back residues and other sources of organic matter like waste products back into the soil whenever it's possible so that the nutrients make a way compost and things like that. So all of that can make a huge difference. It's important, though, to remember that there's a variety of options out there and they're appropriate for different types of environments. So, for example, the 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 for grasslands.

And I mean because grasslands can have roots that are 10 feet deep and are storing all that carbon underground in a place where it can't be burnt up. Exactly. 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 or basically charcoal made from burnt plant material. Yeah, no, there's a whole bunch of options out there.

Some of it includes biochar, which had been shown. 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 it'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. Which is to say 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 sequestrating atmosphere carbon dioxide. So there's a number of these efforts. The important ones in terms of their 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 efforts that we could do that are appropriate for a variety of environmental settings. We humans are facing a lot of crises on this earth, but Asmata 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 Soy Happy World Soil Day, Shortwavers This episode was produced by Rebecca Ramirez,

edited by Gabriel Spitzer, and fact-checked by Ubi Levine and Margaret Serino. Brendan Crump is our podcast coordinator, Beth Donovan is our programming senior director, and Anya Grumman is our senior vice president of programming. I'm Aaron Scott. Thanks for listening to Shortwave from NPR. See you all tomorrow.