Interview
W
hen he was an undergraduate student, David Montgomery stumbled across a book that had been published in 1955. Topsoil and Civilization was the work of Vernon Gill Carter and Tom Dale, two soil scientists focused on conservation. Twenty years after its publication, the treatise hooked Montgomery, who is now a geomorphologist at the University of Washington Seattle. His own book, Dirt: The Erosion of Civilizations, published last year, was inspired by that 1955 book and by many others that preceded it.
Universit y of California PRESS/COURTESY OF DAVID MONTGOMERY
Protecting the SOIL Beneath
David Montgomery, geomorphologist and author of Dirt: The Erosion of Civilizations, talks with ES&T. NAOMI LUBICK
© 2008 American Chemical Society
May 1, 2008 / Environmental Science & Technology ■ 3129
ES&T’s Naomi Lubick asks Montgomery questions about Dirt and why soil must be saved for human civilization to continue. How did you come to write your book? I read [Topsoil and Civilization] when I was an undergrad and loved it. . . . That agricultural societies sort of burned through their allotment of fertile topsoil by indiscriminate plowing was essentially the argument they were making. There was a book in the 1920s that said that, a book in the 1860s that said that, and then Plato said that, what, 2000 years ago? So it’s not the kind of thing that’s a completely new revelation, but every few decades, it is. Our cultural memory of how important the issue is cycles in and out. I quite intentionally wrote this book to cycle it back into the public consciousness. It was my attempt to update [Carter and Dale’s] really good book.
the main culprit. What I like to think of as the tapestry on which the rise and fall of human civilization plays out is how people treat their land. It’s sort of the longwavelength periodicity to human societies, whereas climate changes and wars are the sort of high-intensity changes that are equivalent to pulling the trigger. But the gun is only loaded depending on these broad epicycles of soil formation and erosion.
3130 ■ Environmental Science & Technology / May 1, 2008
COURTESY OF DAVID MONTGOMERY
I thought a lot of this ties into the water cycle, but you are telling me it doesn’t. If you think of the big three resources that humanity must conserve to remain viable ourselves over geologic time, they are the atmosphere and basically the climate, which are linked; there’s freshwater supplies because we are water; and there’s soil because we eat soil processed through plants. If we run out of any one of those things, or we so poison our nest such that we can’t use them, it would be difficult to imagine how humanity could continue. I have to say I’m still a little bit skep We’re very focused on trying to tical about the connection between avoid the effects of climate change soil and the downfall of civilizations. these days, and in the past few I think of the Dust Bowl—we sort of years there’s been a sea change survived that. in awareness—which is fabulous, Yeah, we did, but we’ve also burned something might actually happen through half the soil in that region now. In terms of water, I think the already. So the question is not average person on the street has whether we survived the one-off. David Montgomery is a geomorpholo a pretty good idea that there’s a The question is whether farming gist who has written about civiliza limited supply of freshwater on in the U.S. Midwest will survive tions’ soil-destroying habits as well as other topics, such as the disap the planet and that it’s going to the next 200 years. pearance of salmon in the Northwest. matter to human societies in the The other thing is just the slow next 100 years. rate at which it happens. You are Very few people worry about conserving the soil talking a millimeter-a-year kind of soil loss—it’s hard to notice! You gotta be a geologist to appreciate how as a fundamental resource for society, and yet it is the most fundamental of those resources. But awkfast that is. To most people, it’s like, come on, my fingernails wardly, it’s the one that we lose at the slowest pace, grow faster than that! But if you think in terms of 1000 which makes it very difficult to motivate action to years being a relatively brief interval of time, then stem because, yeah, what’s the big deal if we lose all of a sudden losing a millimeter a year means you another millimeter of soil this year? It’s hard to get that issue to the forefront of socicould lose a meter—3 feet of soil—in 1000 years. And ety’s decision-making apparatus. And that’s why you you start to go, ooh, this actually could add up. see things like [current] biofuels proposals; they’re not even considering erosion effects. You cite everyone from Plato onward. You’ve even got material from 5000 B.C.—obviously archaeological re cords—in places like Iraq, which we think of as the old I’ve heard the arguments against biofuels that bring up Eden. Why did people lose that connection between soil land use, all the pesticides that would be necessary, wa loss and the loss of what used to be a paradise of agricul ter use, but nobody talks that much about erosion. ture? I always thought climate change was the cause. And yet one thing we do know about conventional You can show that climate change was really not the corn is that it’s one of the most erosive agriculturdriver. There were droughts that really hurt ancient al practices that we have on the planet, large-scale societies pretty badly. But if you look at, say, the tim- mechanized conventional corn. We ought to make ing of the rises and falls of the classical Greek land- subsidies tied to no-till agriculture—make them do scape, they were not in phase from one valley to the it right! One of the things that no-till agriculture does is it next. If you had a regional climate shift that did a whole population in, it ought to take a whole area returns carbon to the soil. What’s the one thing we need to do to slow the impact of global warming? It’s out. One of the things that I was impressed with while get carbon out of the atmosphere. If we were to actudoing the background research for the book was how ally promote the aggressive restoration of our soils clear the evidence was that climate change was not by increasing carbon content, it would make them
When it comes to land management practices, there are obviously some that are better than others. But I look at places like China and I see that farmers there may be ter racing and therefore conserving their soil, but they’re not doing so hot either. The Chinese destroyed their ancestral agricultural homeland [described in Chapter 7 of the book]. . . . Where they first started farming [the headwaters of the Yellow River in northern China], they blew through their soils. When they started to get into terraced wetland-based rice agriculture, the erosion rates probably went way down. The cool thing about wetland rice agriculture—rice paddies—is that there are nitrogen-fixing bacteria that live in the water, so there’s a natural fertilizer. But you can’t give the Chinese credit for showing that you can sustain agriculture for a long time, because they’ve shown pretty compellingly that they can burn [through] soils as well as the rest of us. [Because of levee-building for flood control,] the Yellow River sits 120 feet above its flood plain. It’s scary. All it’s got to do is jump its banks and there’s a lake the size of the entire floodplain, [flooding] cities with millions of people in them. The reason that they mobilize the Red Army to put sandbags on the river when it floods is that if a city floods 120 feet deep, that city doesn’t survive—especially when the buildings are only two stories tall. [In the U.S.], what’s happened in the Mississippi is the amount of dirt getting down to the mouth has gone down. We’ve increased erosion rates on the hillsides by 10-fold. And we’ve decreased the amount coming out the bottom by half. Where is it all ending up? Behind dams, on floodplains. There’s also the problem that a lot of the sediment is being shot off the continental shelf, by being trapped between the levees [instead of flooding surrounding plains and settling there]. The half that we’ve decreased is going out there; the other half is being parked upstream in reservoirs and on floodplains and in hillsides downslope of farms, which means that New Orleans is sinking because we shut off its sediment supply. And that’s typical of many big rivers around the world. In terms of some of the ways that we need to change our farming practices, it seems to me that people have been working on this for some time. The whole no-till thing seems to be catching on. When I was born, there was virtually zero to no notill farming. At the moment, [about] one-third of our cropland is farmed using no-till methods. We’re already a third of the way there in 45 years. So maybe in 100 years after I was born, we’ll be all the way there. . . . These processes happen so slowly, that if we were able to do it in the course of a century, it
may stave off the worst effects one might find from agricultural degradation. That’s the optimistic side: we’ve actually made great progress, and the U.S. is one of the world leaders in no-till agriculture. [But] it’s not because our agricultural subsidies are promoting it, quite the opposite: It’s because it has made economic sense to do so. If you look at the pessimistic view, . . . we’re gearing up to promote major biofuels programs in the Midwest. This is all conventional corn, all massively subsidized, and subsidized to grow corn in ways that are very erosive. We have the potential to undo all the good soil conservation work of the past few decades with a decade of very aggressive biofuel promotion. USDA
more fertile, which would mean we would need less fertilizers, and it would sequester huge amounts of carbon. . . . It’s conceivable that if you had some kind of carbon trading system, [you] could set up the incentives for farmers such that they not only could afford to do no-till farming, but that it would be profitable for them.
The massive erosion across the Great Plains of North America in the 1930s came to be known as the Dust Bowl. The U.S. Midwest lost about one-third of its topsoil, as documented by USDA career soil scientists.
That’s the scary part. If we basically trade a form of agriculture that’s dependent on fossil fuels for one that’s based on using up soil, then we’ve just traded a system that mines one thing for a system that mines another. And if there’s one thing we know, it’s that if you are mining a resource, you eventually run out. The flip side of this point is that once you lose soil, you have to make up for it with chemistry. There’s been a long history of doing that in the 20th century, where crop yields went through the roof because of the Green Revolution, because of the clever and effective use of chemical fertilizers. You are essentially using agrochemistry to replace soil fertility. That’s something that, as long as one has access to the ability to make large amounts of cheap fertilizers, you can keep going. There have been a few studies since I wrote the book, or that I became aware of since I wrote the book, that suggest that the nutrient content of foods grown in fertilizer-intensive environments is different than organic foods. If you think from the geologist’s angle about that issue, what’s the one thing we are projected to run out of in the next 100 years? Cheap petroleum. Most May 1, 2008 / Environmental Science & Technology ■ 3131
People in [developed countries] aren’t going to want to have everybody work part-time on a farm. It’s convenient to have 2 out of 100 people work on farms so the rest of us can do other things. But for those places, thinking about how we actually farm, large-scale no-till agriculture could demonstrably get erosion rates back down to something like the background geologic rate. We know how to farm and conserve the soil. It can be done.
NASA
of our nitrogen-based fertilizers are generated from natural gas feedstock, and large amounts of fossil fuels are used to crack atmospheric nitrogen to combine it into a biologically useful form. So, if we run out of large supplies of cheap energy, then we’re going to have a hard time maintaining large amounts of fertilizer production. If we continue to degrade our agricultural soils at the rate we are, and we make up the difference in lost soil fertility by fertilizer subsidies, what happens when we run out of the ability to make cheap fertilizers? . . . That’s a scary scenario.
Dust storms carry soils from China’s Loess Plateau, ob scuring the Yellow Sea from satellite view and some times reaching as far as the U.S. The Yellow River also carries silt downstream from the northern region; flood ing along the river is checked by high dikes and levees.
What about the promise of organic agriculture? You hear from agribusiness the idea that organic cannot feed the world. It’s almost like a mantra . . . and yet there have been many studies that show that the highest crop yields on the planet are from small-scale organic farms. . . . What I tried to do in the last chapter [of the book] is lay out how there might be different paths forward for the developed world and the developing world. What subsistence farmers and poor people have in the developing world is their labor and time. What they don’t have is money. I think one of the great failings of the Green Revolution is that if you have people who are too poor to buy food, growing it in an agrotech environment won’t help them because they won’t have any money to pay for it. . . . The only way that you will feed them is to give them the opportunity to do so themselves. Therefore, small-scale, labor-intensive farming, land reform—those issues could probably solve the problem of hunger [in developing countries]. 3132 ■ Environmental Science & Technology / May 1, 2008
There’s one chapter where you talk about how animals feed into this process. Does that mean you are a probiosolids kind of a guy? If you look at the really big picture, far enough down the road, we need to take all the organic stuff that we’re producing, running through our bodies, and throwing away as food we don’t eat, and recycle that back into soil fertility. . . . There’s good reason to think that if we recycle organic matter and nutrients, nitrogen and phosphorus in particular, that [we] could develop sustainable agriculture that way. But there’s a whole host of public health issues, infrastructure issues . . . some of that stuff, I wouldn’t want that sprayed on farmland! I’m personally very interested in the idea of how one could get urban environments to practice largescale composting. The whole biochar movement, and large-scale urban composting, is something that makes a lot of sense to me, and urban agriculture makes a lot of sense to me as well. One of the things that I did not know before writing the book . . . was just how productive urban farms can be. The city of Havana grows all of its vegetables within city limits. Like 19th-century Paris, [which] did the same thing, except they used horse [manure], recycling their transportation effluent. In Cuba, they got pretty wild about organic. They got cut off from oil supplies and fertilizer supplies when the Soviet Union crashed. So they are the experiment for what will happen when we run out of fossil-fuel-based fertilizers. And they did it, but they did it by changing the way they farmed. A single point in the book that I’m trying to advocate: If you look [at things] like a geologist [does] over the next couple hundred years, we need to change the way that we farm. Because if we go the same way as ancient civilizations and erode through our soil, then our basic trajectory is down. It’s not like we’re going to collapse overnight because of soil erosion. I’m not arguing here that any society ever did that, but our overall trajectory will be down. Which means that climate change, or wars, or any of those other high-frequency blips might take us out. Naomi Lubick is an associate editor of ES&T.
Further reading
Montgomery, D. R. Dirt: The Erosion of Civilizations; University of California Press: Berkeley, CA, 2007. Montgomery, D. R. Soil Erosion and Agricultural Sustainability. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 13,268–13,272.
