Enhanced rock weathering is a method that uses crushed volcanic rock to improve soil health. Ann Leslie Davis is a freelance science writer and recently covered the issue for Modern Farmer. We hear more from Davis about her reporting, how volcanic rock dust can help overworked soil and how farmers feel about using the method.
Note: This transcript was computer generated and edited by a volunteer.
Dave Miller: This is Think Out Loud on OPB. I’m Dave Miller. Happy Friday. Modern Farmer, a nonprofit online magazine devoted to agriculture and society recently published a surprising article. The opening scene focuses on a wheat farmer outside of Pendleton who was given an offer that seemed too good to be true: free crushed rocks to make his soil less acidic. He said, yes. What follows is a story about agriculture, climate change and international markets. Ann Leslie Davis wrote it. She’s a freelance science writer and she joins us now. Welcome to the show.
Ann Leslie Davis: Thank you, Dave.
Miller: Your article is about this new way that farmers like the one I just mentioned and Pendleton can make their soil less acidic. And that’s not unusual. Why might farmers’ soils be acidic these days in the first place?
Davis: Well, Dave, soils can vary in pH and some are naturally acidic. Areas that have a lot of rainfall or particularly soil type can be acidic, but there are a couple of major factors that in traditional farming make soil acidic. One is harvesting all the organic material, removing it from the field after harvest time, so none of that material is left to then decompose back into the soil or a major culprit is nitrogen fertilizer. Nitrogen fertilizer is good for plants at first because it releases nitrogen, but when it releases nitrogen, the breakdown product is acid and so that acid is released into the soil and then the soil over time becomes more acidic. So this is a growing problem in Oregon and in many US states and really in croplands around the world.
Miller: Why is acidic soil a problem?
Davis: Well, plants don’t like it.
Miller: That seems pretty simple. [Laughter]
Davis: Plants can thrive in a really small window of the pH range. If we go back to high school science, pH 1 is like battery acid and [pH] 14 is like Drano, then pH 7 is neutral and that’s where plants like to live, that’s where they’re happy. If the soil is too acidic, roots can’t absorb the nutrients they need. The acid in the soil can release some things in the soil that are toxic to plants. Sometimes the nutrients themselves will leach down to a level below where the roots can reach them. And if it’s really acidic, those beneficial microbes that are in the soil will die. So plants need the microbes, they need the nutrients, they need all of these things and they can get them when the pH level is about between six and seven.
Miller: What options have farmers had in the past if they wanted to make their soil less acidic?
Davis: Farmers have used ag lime. That is, I think that’s the most common thing. That’s what most farmers are using today. And ag lime is a good product. It will help make soils more basic, but from an environmental perspective, there’s a lot of CO2 emitted in the creation of ag lime because the processing creates a lot of CO2 and farmers have to pay for ag lime. The great advantage to farmers with the process that’s described in the article is that this new material, this crushed rock, is not only provided for free, but the little start up companies that are out there will spread it for the farmers and monitor the soil.
Miller: We’re going to get to the weird economics of that in just a second. [Laughter] But first, can you just, can you just describe what this technology is? And that word seems a little bit fancy for what we’re talking about. It’s called enhanced rock weathering. But is that just a fancy way of saying crushed rocks?
Davis: Yes. You’re grinding up rocks, you’re grinding them up into something really small.
Miller: What’s the idea behind this rock dust?
Davis: Well, to answer that I want to first explain what rock weathering is. It’s a geological process on earth. So, if I could take you back all the way back to the cretaceous where the dinosaurs are roaming and volcanoes are spewing lava and clouds of gas, back then the CO2 levels in the atmosphere were five times what they are today. So the question is, why aren’t we still breathing the same air that the dinosaurs breathed? And the answer is rock weathering. So in nature, rain and CO2 in the atmosphere combine to form a weak acid and when this acid hits volcanic rocks, it causes a chemical reaction that binds CO2. And this has happened over millennia. This acid is not the same, by the way as acid rain, that’s different. But it’s happened over millennia and it’s just earth’s thermostat, it’s earth’s way of regulating temperature on the planet.
So now moving from that to enhanced rock weathering, which is really just grinding up rocks like you said, this process just speeds up the natural process. Because when you grind up these volcanic rocks that can capture CO2, you grind them up tinier, it increases the surface area that’s available to capture CO2. So a lot more can be captured.
Miller: So this gets us to the economics. As you outlined in the article, a company like Microsoft can buy carbon credits. And meaning if I understand this correctly, give money to some startups that then crush rocks and then deliver that rock dust for free, spread it out on a farmer’s land for free. And so the company gets money from Microsoft, the farmer gets the dust and theoretically this less acidic soil and Microsoft, as one example, doesn’t have to reduce their own emissions. They’re buying an offset somewhere else. So that’s how this works.
Davis: Correct.
Miller: Is anyone actually verifying that more CO2 is actually being sucked up once this rock dust is being applied?
Davis: The answer is a big yes. So the companies themselves have pretty elaborate verification methods, measurement and verification methods. They go out into their fields, they do test plots and control plots. They do very detailed measurements of soil pH before and after. Different companies have different ways of measuring that but beyond the company which might have its own vested interest in showing that the pH goes up, these companies are all verified by independent institutions that have been created in this climate space where companies are grappling to deal with climate change. Verification companies have risen up in this field and monitor and give their approval after a very lengthy process to these companies. So, yes, they are quite thoroughly checked out.
Miller: Where did these crushed up rocks come from to begin with?
Davis: Well, Oregon, where you are, is a source of a lot of basalt. So basalt is the most common rock on earth. It’s a volcanic rock, it underlies most of the ocean, but there is a volcanic outcropping in a big one in Eastern Oregon, part of the Colorado Basin, where there’s a lot of basalt. And so these companies can get the basalt from natural outcroppings like that and they are specifically getting the rock often from quarries or as mine tailings. So they’re getting rock that is sitting around that’s a waste by-product of a mining or quarry process.
Miller: That led to some skeptical comments in response to your article on the Modern Farmer website. One person wrote about concerns that “Mine tailings themselves are highly contaminated” and “Of course, mine owners would be happy to send their pollution elsewhere.” Another person wrote, “What is the heavy metal analysis of the crusher dust?”
Do you know if anyone is checking to make sure that farmers essentially aren’t getting free poison?
Davis: Yes, that’s a good question. Yes, basalt is low in nickel and other minerals that might be toxic. So there are different kinds of volcanic rock and some of these have very low mineral levels, some have higher mineral levels like olivine which is another rock. But the rock is analyzed and tested for its content within these companies so that they are not, in fact, spreading poison, as you said.
Miller: Ann Davis, thanks very much.
Davis: Sure. Thank you.
Miller: Anne Davis is a freelance science writer. You can read her article about what’s now known as enhanced rock weathering, basically using crushed volcanic rocks to make soil less acidic and to have it capture more carbon. The recent article is in Modern Farmer.
Contact “Think Out Loud®”
If you’d like to comment on any of the topics in this show or suggest a topic of your own, please get in touch with us on Facebook, send an email to thinkoutloud@opb.org, or you can leave a voicemail for us at 503-293-1983. The call-in phone number during the noon hour is 888-665-5865.
