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Exploring the connection between soil health and human health

February 9, 2023
David R Montgomery on the Crop Science stage at the 2022 Alltech ONE Conference in Lexington, Kentucky

David R. Montgomery, MacArthur Fellow and professor of geomorphology at the University of Washington, is the co-author of "The Hidden Half of Nature: The Microbial Roots of Life and Health" with his wife, biologist Anne Biklé. Their latest collaboration, "What Your Food Ate," explores connections between soil health and human health.

In this episode of the Ag Future podcast, David Montgomery, a MacArthur Fellow and professor of geomorphology at the University of Washington, discusses how soil health can affect human health and the environment. David, the co-author of the books "The Hidden Half of Nature: The Microbial Roots of Life and Health" and "What Your Food Ate," examines how regenerative farming practices can rebuild and maintain healthy soils. Join us as we dig into the world of soil and explore its vital role in agriculture and human health.

The following is an edited transcript of the Ag Future podcast episode with David Montgomery hosted by Tom Martin. Click below to hear the full audio or listen to the episode on Apple Podcasts, Spotify or Google Podcasts.

Tom:            Welcome to Ag Future, presented by Alltech. Join us from the 2022 Alltech ONE Conference as we explore opportunities within agri-food, business and beyond.


                     People, plants, food, health (and) the environment (are) all connected in some way or another, and paying close attention to those connections is our guest for this episode in the Alltech Ag Future podcast series.


                     I'm Tom Martin, and with me is David Montgomery, a MacArthur Fellow and professor of geomorphology at the University of Washington. He is an internationally recognized geologist who studies the effects of geological processes on ecological systems and human societies. His work has been featured in documentary films, on network and cable news, and on a wide variety of TV and radio programs, among them NOVA, PBS NewsHour, Fox and Friends, and NPR’s “All Things Considered”.


                     David is the co-author, with his wife Anne, of “The Hidden Half of Nature: The Microbial Roots of Life and Health,” a book that examines our tangled relationship with the microbial world through the lens of agriculture and medicine. Their latest collaboration, “What Your Food Ate: How to Heal the Land and Reclaim Your Health,” explores connections between soil health and human health. David is here to help us sort out our tangled relationship with microbes, plants, food, health and the environment. Welcome to Ag Future, David.


David:           Well, thank you. It's pleasure to be here.


Tom:            David, you have dirt on your hands. In fact, you have literally written the book on the subject. It's titled “Dirt”. Tell us about that thing that is most vital to life: soil.


David:           I’m a geologist, so, by training, I was taught to look past the soil to the rocks underneath. But in the last 15 years, I've really come around to seeing that soil is one of our most valuable — and least-valued — resources, planetarily. We rely on fertile soil to feed ourselves. Civilization after civilization has been built on fertile land. The societies in the past that have degraded their land to the point that (it) impacted their agricultural productivity? Those are the ones that did not last.


                     We've been writing about soil and its importance for civilization health, and now, (we’re) looking at the health of us (humans) as individuals. It's something we should all pay a lot more attention to and care more about, because just like we have health — and for good or bad — the soil can be healthy or unhealthy as well. Most of us don't think about it that way. We tend to take soil for granted and treat it like dirt.


Tom:            There's a great Kentuckian, the poet and writer Wendell Berry, who has commented many times that when we scrape away topsoil, we're actually scraping away millennia of development there. I don't think we do appreciate what's at loss when we do that.


David:           Yeah, when you think about how long it takes nature to form fertile soil, you're talking centuries to millennia to form an inch, a simple inch. When you look at how fast topsoil can erode under conventional agricultural practices — tillage, primarily, because that accelerates erosion by water (or) by wind — we can lose that same inch in decades. That imbalance — something that we can lose in decades but that takes centuries to rebuild — is something that means that we're losing it, slowly but surely. That's been the story of society after society around the world. But we don't have to do that. We can actually turn it around and rebuild healthy, fertile soils, and do it remarkably fast. It just takes a different style and way of farming.


Tom:            I think we think of it as inanimate, but isn't it what's in that soil — and, to that point, what lives in that soil — that determines not only the health of a medium that plants grow in but, also, our own human health?


David:           Yeah, and the health of our crops and the health of our livestock, that — you can trace connections from soil life and its abundance, the community composition of it, its health, if you will, right on through to human health. That's what we do in “What Your Food Ate,” the new book (I co-authored), and it turns out that the life in the soil — the whole subterranean ecological system of microbes, bacteria and fungi, and worms and little arthropods, and all that life in the soil — is really important for cycling nutrients, getting them out of the mineral particles that are in rocks and getting them into the crops so that they can get into our livestock and into us.


                     That life in the soil also has a long history of partnerships, of symbiotic relationships with plants, that we kind of neglected and forgot about in our modernization of agriculture in the 20th century. We paid a lot of attention to physics and chemistry — which, of course, are very important in terms of soil health, soil fertility and crop production. But biology is the part that is now coming back into the forefront of thinking about, “Well, how do we not only maintain high crop yields today, but how do we keep doing it into the future?” Because that simple story is that our conventional mix of agricultural practices today has been degrading land for a long time, and we've been using agrichemicals to sort of cover that up and compensate for it. But to maintain it over the long run, biology is really the basis for a solid foundation for sustainable agriculture.


Tom:            How would you define regenerative agriculture, and how does it compare to traditional and organic farming?


David:           Yeah, there's a lot of arguments today about how we should define what's labeled today as “regenerative agriculture”. I consider it (to be defined as) farming practices that build and enhance the fertility of the soil as a consequence of farming. I like that simple definition primarily because, in looking back at the history of past societies in writing “Dirt,” the common element, in terms of societies that “went out of business,” shall we say, is that they degraded their land through their farming practices. We can't afford to do that at a global scale today. We need to regenerate soil fertility, rebuild soil fertility. There's lots of different ways to do it.


                     When you take the definition I just offered, it's a fairly broad-tent, broad-umbrella kind of a view of it. In relation to conventional and organic farming, there's ways to do both regeneratively, but to do conventional farming, generally, one has to so greatly reduce the reliance on agrichemical inputs and synthetic fertilizers as to be moving really close to organic farming. What organic farming needs to do to go regenerative is to disturb the soil less and do less tillage. There's sort of multiple paths, in my view, for getting to regenerative (agriculture), but they're both dependent on prioritizing building the health of the soil, which means that there's particular ways of doing things that would work in those two different systems.


                     The combination of practices that appears to work really well is to minimize disturbance of the soil, to keep living plants growing in the soil at all times — and that translates into cover crops — and to grow a diversity of crops. They're not simple two-crop rotations, but one can get that diversity in either through the cash crops or through cover crops. There are different ways to get at that same idea of trying to build soil fertility and build soil health as a consequence of farming. But when you look at it at that simple level, it would be a real sea change if that was sort of the underlying objective in agriculture, as opposed to maximizing yields over the short term, which is where we've pretty much gone for last 80 years.


Tom:            Why is that diversity of crops important?


David:           Yeah. When you think about those three practices, the “minimize disturbance” is important, because if you're plowing up mycorrhizal fungi, for example, you're breaking their connections and their life that actually are central to getting nutrients delivered from the soil into the plants. If you look at cover crops, they're essentially feeding that microbial community for exuding carbon-based substances into the soil that those microbes eat and rely on and provide benefits to the plants in return.


                     That third piece, the diversity, I like to think of in terms of, “How functional would a baseball team be if it was made of all catchers or all pitchers?” It's just not going to do the same thing, as a team, that a fully outfitted team of all-stars could do, for example. When you look at soil life, it's kind of similar. Different plants will exude different compounds to recruit different microbes, and a community of microbes in the soil can actually do more for the next crop or sequences of crops for building health. They work better as a team.


                     It's — the diversity really comes in in terms of a diverse suite of plants growing above-ground, (and that diversity) is going to be reflected in a diverse suite of organisms below-ground. And that minimally disturbed, well-fed diversity of soil microorganisms is the recipe that seems to work for suppressing pathogens, for enhancing the benefits that flow to crops (and) maintaining yields with lower inputs. That simple combination can work really well. There are opportunities to enhance that through intelligently managed livestock grazing, for example, but it's just not the way we intended to do and intended to teach it for the last 100 years.


Tom:            Well, what can the regenerative approach to farming do to support efforts to deal with climate change?


David:           The regenerative farms that I've visited around the world that have been very successful at rebuilding the health and fertility of their soil — and what my wife did to our garden at home — and turning it into a very fertile land is all reflected in the color of the soil, going from sort of a degraded khaki color with very little organic matter to a rich dark or black color, and that difference is due to carbon being integrated in the soil organic matter and that building up in the soil. That carbon all came from the atmosphere.


                     I mean, there's a very, very powerful way to take carbon from the atmosphere and sequester it, if only for the short term, depending on where it goes, and that's known as photosynthesis. Plants grab carbon from the atmosphere, build biomass out of them, and eventually, some of that gets into the soil. And the darkening of soil under regenerative agriculture can basically keep that carbon in the ground, put more of it in the ground than had been there before. Much of it will cycle. It doesn't necessarily stay there all the time. But if you have more of it coming in and less of it going out, you can build it up to it, and that's what's reflected in the darkening colors of regenerative agriculture.


There's lots of arguments today about how much carbon could be put in the world's cropland soils as a result of regenerative agriculture. I think the jury's out still in terms of the number that one might point to as, “Oh, you could do this much.” There's a lot of variables involved, and the answer is probably not the same (for everyone) depending on where you are in the world, and sort of integrating that becomes horribly complex. But the short answer is: A lot. You could probably (sequester) on the order of maybe a quarter of the world's fossil fuel emissions fairly reasonably if a lot of farmers adopted these regenerative practices. That may not sound like solving the climate problem — and it won't at those kinds of numbers — but it's a big down payment on doing so.


                     I think that what we might want to focus on, in addition to the carbon going into soils, are all the other benefits that can flow from increasing the carbon in soils and increasing soil organic matter. We can maintain the productivity of our land. We can enhance the water storage capacity of our soils and the ability of water to infiltrate, to sink down into the soil, and so not to run off over the surface. That translates into crop resilience to droughts and climate change.


                     The latest thing that we talk about in “What Your Food Ate,” the new book (that I co-authored), is looking at what increased soil organic matter and soil health can do to the traditional quality of food. We did a bit of a study around the U.S. comparing regenerative farms to conventional farms, and we found that not only could the soil organic matter content be, on average, roughly doubled in the uppermost part in the topsoil, but it also affected the nutritional profile of foods, increasing the mineral composition of certain micronutrients and certain crops but also increasing the vitamin content, again, in certain crops and, almost across the board, increasing the phytochemical content.


                     What are phytochemicals? Those are plant-made compounds — literally what the name says — but those are things that have anti-inflammatory, antioxidant effects when they then get into our body, and our microbiome in our gut diet helps us digest them and their metabolites. What they turn those compounds into (can) have demonstrated medical effects in terms of reducing many of the root causes of what we now know of as an epidemic of modern chronic diseases. There's a lot of ancillary benefits to improving the health of our soil, one of which — and a very important one of which — is the climate connection, but there's a lot of other ones that go along with it.


Tom:            Drought is becoming severe in many parts of the world, including the American West. How can soil be made to resist a loss of moisture?


David:           Well, there are two ways to make soils resist loss of moisture. One is to get more moisture in the ground in the first place, and the other is to essentially keep it there. Regenerative farming can help with both in the sense that if we're tilling land regularly, if we're plowing it all the time, you're breaking up the structure of the soil, and if you think of soil as having conduits through which the rain that falls on the surface sinks down into the ground to get to the roots of plants. But what happens when you break up those moisture highways? You create a crust at the surface. I've been in many fields that are so crusty after just a little bit of a rain. It's kind of like if you take a bag of flour and put it out in the rain. What happens? All the flour at the bottom of that bag doesn't get wet. The stuff at the top crusts over, and then, essentially, water would run off over the top of that.


                     Soil is very similar once it's been powdered by tillage. Regenerative farming can get more water down into the soil. If you always have the land just covered with a mulch, it's better at keeping the moisture in the soil. (I’ve seen) figures that, if I can remember them properly, (say) that for about every 1% increase in soil organic matter, you can store like 20,000 acre — (or) feet of water in an acre for that increase. So organic matter-rich soil, healthier, more fertile soil can essentially recruit more water — can capture more water, is a better way to put it — from precipitation, but it can also keep it there better in ways that it actually gets to the crop. That's what translates into crop resilience to drought.


Tom:            You touched earlier on carbon-capture sequestration. What advances are being made in the science of pulling carbon from the atmosphere and returning it to the soil?


David:           Well, that combination of principles: If you combine no-till with cover crops and a diversity of crops, it’s a pretty good recipe for feeding the microbes in the soil, whose dead bodies then become the soil organic matter that can turn a khaki color into a rich dark-chocolate color. There's lots of ways to do that in terms of the specific practices, but there are general principles of minimizing disturbance, keeping living plants growing in them, and recruiting a diversity of microbes, which means growing a diversity of crops. (That) is a recipe that's proven and seems to work pretty well.


                     It's not enough to just go no-till. The studies are kind of one way or the other: It can increase or decrease soil organic matter depending on the location. Cover crops tend to help increase it, but where people (have) found the biggest increases are if you do all three together. That makes a lot of sense because that's essentially how you cultivate a beneficial community of microbes in the soil. If you're basically harvesting their bodies to build the soil organic matter, you want a thriving, abundant community of life in the soil.


                     There are different ways to do that. There's a lot of arguments over how to measure it and how to think about how much to keep there (and) for how long. There's plenty of arguments, still, about that. But I think we kind of know the broad outlines of what we might think of as a new farming system that could help build soil organic matter to the (greatest) extent possible in different areas. In “Growing a Revolution,” a book that I wrote between (writing) “The Hidden Half of Nature” and “What Your Food Ate,” I visited farmers around the world who shared their methods for building soil organic matter that were very different in Ghana from Costa Rica or the United States, but they all follow those three simple principles I mentioned.


Tom:            Can regenerative farming in a farming community make a difference to that community’s local economy?


David:           That was one of the big questions that I (asked myself as I) went into writing the last couple books on (farming). What I found was — the short answer is yes. The longer answer is (that) what I found is that the farms that had been very successful at rebuilding their soil, at cultivating fertile soil and putting a lot of organic matter back into it, had been able to greatly reduce their use of synthetic fertilizers. Why? Because they didn't need so much of them. They greatly reduced their use of pesticides. Why? Because they didn't need so much of them, and they burned less diesel. Why? Well, if they're not plowing, if no-till is that first piece of the puzzle, then they're driving tractors across your fields roughly half (of) the time. If you translate that into the actual operating costs of a farm, those three things — fertilizer, pesticides and diesel — are three of the big-ticket items for modern farms in the developed world.


                     If one can basically — by rebuilding the fertility of the soil, and (if you) do it as a productive farm and cut down your input costs, if you're harvesting the same amount or comparable amounts and you're spending less to do it, it's a recipe for a better bottom line for the farmer. That's what started (to) turn me into an optimist on the issue of whether we could really turn around the state of the world (through) farmland soils, because a system that works for farmers is one that may, itself, be sustainable in terms of agricultural economies.


                     I've visited a lot of farms across North America in the last 10 years, thinking about these issues and writing about them. There's an awful lot of small towns with boarded-up main streets, and it's kind of a side effect of going from small farms to really big farms. One of the things that regenerative agriculture can do is help make smaller farms more profitable. Of course, it can make large farms more profitable as well, but there's different methods and technologies and equipment that one needs based on that. But I view farming practices that can rebuild the health and fertility of the land as, actually, a very solid foundation for trying to rebuild and enhance the economic situation of rural regions, not just in the developed world but all around the world.


Tom:            We're very busy creatures, we humans. It seems to make sense to, at least once in a while, slow down and think about that — think about how we fit into the whole food-chain picture. Do you find that, as a rule, we don't do that as often as we ought to, if ever?


David:           Yeah, I think that's a good way to put it. I mean, many of us in the Western world think about food as something we grab out of the grocery store. We don’t try to trace it back to thinking about how it was grown, where it was grown, what it means for the people who are growing it along the chain. Yet one of the things that has really come into great focus for me in writing “What Your Food Ate” was (the fact that) how we grow our food actually ends up mattering to our own individual health.


                     I think that may actually help us, as individuals, put more focus on thinking about the path that our food took, from field (or) farm to fork, and thinking about that. Because the kinds of things that we've been able to see that farming practices can influence are things like the mineral micronutrient content of our food, the vitamin content, the phytochemical content, the polyphenols, the antioxidants and anti-inflammatories in fruits and vegetables, in particular, but also in even things like grains, and also in terms of the fat composition of our meat and dairy products.


                     It turns out that it matters what our food ate, for (that impacts) what is in that food and what that, then, does when it gets into our bodies. It's less about, really, sort of preventing infectious diseases. I mean, modern medicine has become really good at preventing infectious diseases, the recent pandemic aside; that's sort of a whole different story. But if you look at the kind of disease profile in the Western world and how it's evolved over the last half-century, we've pretty much got infectious diseases under reasonable control, unless there's a pandemic. But the epidemic of chronic diseases has just exploded since we adopted modern agricultural techniques after the second World War.


                     There's a number of probable causes for that. One is what we're choosing to eat, how we're processing our food. But (my wife) Anne and I became convinced, based on the research we did for “What Your Food Ate” and the bit of data and the studies that we've sort of conducted along the way, that there's another piece of that, and that's how our food is raised, how our food is grown — and that we should really all be caring about what our food ate, which, for crops is how we fertilize it, how we grow it for our livestock. It's what they're eating and how it was grown. In the book, we try and trace the scientific connections between each step along the way for how the way we treat the land affects the soil health, how soil health affects crop health, how crop health affects animal health, and how the latter two directly or indirectly affect human health.


                     The connections are complex. There's a lot that goes into our own individual health. There are our genes, our genetics. There's whether or not we get any exercise. There's what we choose to eat. There's also, I think, how our food is raised.


Tom:            All right, that is David Montgomery, MacArthur Fellow, professor of geomorphology at the University of Washington, and co-author, with (his) wife, Anne, of “What Your Food Ate: How to Heal the Land and Reclaim Your Health”. Thank you, David.


David:           Thank you. It's (been) a pleasure to talk.


Tom:            For the Ag Future podcast, I'm Tom Martin. Thank you for joining us. Be sure to subscribe to Ag Future wherever you listen to podcasts.