Sustainability through Massive abundance.

Episode 14: Losing Soil

Why civilization after civilization squandered their soils and fell, why soils are even more imperiled in the modern world, and how cities can learn from these mistakes. If Episode 13 was like Stanley Kubrick's 2001, this episode is like The Empire Strikes Back.

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What's the biggest problem?
Intro [music]
Lifespan of Civilizations
Fallen Civilizations
Modern Folly
Status Today
Design Takeaways
Close [music]

What's the biggest problem?

What's the biggest problem in the world today?

In his massive online permaculture design course, Geoff Lawton, perhaps the world's leading permaculturist, said it like this: he said our third biggest problem is pollution, including carbon dioxide, which causes climate change. Our second biggest problem is deforestation, and our first is soil erosion.

Soil? Really? What does soil do for us? Well, in short, no soil, no food. Not just for people but for all of land life, which maintains a pleasant environment, prevents dust storms as we'll see, absorbs waste, cools the planet, keeps the atmosphere breathable, maintains waterways and oceans. Okay, it's basically irreplaceable.

Now, in Episode 13 we talked about how soil is alive. It's high tech, and there is no artificial substitute in the near future. Soil is Earth's highest technology.

But there's so much of it. How could we ever run out? Well, today we'll count the ways so we'll know what not to do if we want to have a permanently wealthy civilization.

Intro [Music]

Cities designed like modern Edens, for economic and ecological abundance. I'm Kev Polk, your guide to Edenicity.

Welcome to Episode 14: our second installment in the Edenicity soil trilogy. If the first episode was otherworldly, perhaps like Stanley Kubrick's 2001, today's episode is a little bit more like The Empire Strikes Back, the second of the middle trilogy of the Star Wars saga.

I'll be drawing on one major source today, and that's David R. Montgomery's 2007 book, Dirt: The Erosion of Civilizations. That should give you some sense of the gravity of what we'll be talking about today. I'm also going to borrow a little bit from Richard Register's 2006 book Ecocities: Rebuilding Cities in Balance with Nature.

Lifespan of Civilizations

One of the central questions behind Montgomery's book is how long do civilizations last? Well, that's going to depend on when they run out of soil.

Civilisations are recent. According to Montgomery, they only began about in the last 1% of our history as a species. Before that, we were hunter gatherers. No sowing. No harvesting, little storage or hoarding. Food was generally abundant and shared by all in a clan. So think about that. That's a real contrast to how we live, and the demands on the landscape are very different for a hunter gatherer society. It takes about 20 to 100 hectares to support a person in that lifestyle, so the Earth's carrying capacity would be about 150 million to 750 million. Now in the time frame we're talking about—a couple of million years ago—there were less than 100,000 people in the African cradles of civilization. So we were well below our carrying capacity as a species.

Population pressures were locally quite strong at times, and there were times when people basically had to stay put. This led to slash and burn agriculture where people would clear some forest and domesticate some animals and maybe plant some additional fodder for them to eat. These would be grain crops, and they would require 2 to 10 hectares per person, so 10 times less land than hunting and gathering.

Now as this process progressed, people domesticated animals, domesticated plants, and we started to be able to have a much higher population density on the landscape and indeed our population rose. Today. We have to get by on 2/10 of a hectare per person. That's 100 times less land than our hunter gatherer ancestors had available, so now we really need to know something about the dirt that we depend on for survival. According to Richard Register, today our biomass as a species is 100 times any large land animal that has come before, so we really need to know something about soil.

So let's go over its basic structure. At the top, there's an organic layer with duff, litter and other natural mulch. And this layer could be anywhere from a few centimeters to meters thick in places where you have accumulated leaf litter from several years of deciduous forest.

Beneath that is the topsoil. This would be the A horizon to a soil scientist, and this is what we normally think of as dirt. This is very rich in minerals and nutrients. It's got quite a bit of organic matter in it. It's usually dark, and it erodes when exposed. Oh, and it's centimeters to meters thick.

Beneath that is the B horizon or the subsoil. This is mostly mineral clays, and it's usually about a meter thick.

And finally below that is the C horizon or the bedrock, and this is weathered rock, from which soil is produced through chemical weathering and mechanical processes: heating, cooling, rain and lots of biological processes. Vegetation, soil, microbes and worms weather the bedrock. Over time, the bedrock sort of shields itself with the upper layers, slowing this process. There's kind of a natural mechanism that regulates the speed at which soil is produced.

Charles Darwin's final studies in his life concerned earthworms plowing the soil. And basically he calculated that earthworms should be able to wear down mountains about 10 times as fast as they actually are worn down. And the thing that he didn't realize at the time is that the mountains of the earth are actually floating on the layers below them. And so as you weather and erode the upper layers and those are washed down eventually, the mountains simply float up like a cork or an ice cube. And so they don't wear down nearly as fast as you would think from erosion. And this process is called Isostasy or isostatic rebound. So nature balances erosion and soil creation, and the other thing that is implicit in this process is that as nutrients are washed down into the oceans and eventually subducted into oceanic trenches, they're recycled back into volcanoes and mountain building events and eventually are available for life to recycle.

The other thing to realize about soil is that it is very thin. If you were a planet, your skin would be 10,000 times thicker than the soil that covers the Earth. Civilisations can feed themselves only so long as they have topsoil. If they speed erosion, they will run out. Their lifespan is equal to the soil depth divided by the net rate of soil loss. Now the natural production rate is very slow, less than a millimeter a year. So if you run out, nature cannot restore it to the several centimeters you need to actually grow crops before your civilization has to move—or before you starve.

Fallen Civilizations

So let's talk about how civilizations have lost their soil and fallen. The story begins not too long after wheat was domesticated in Damascus, in western Syria about 10,000 years ago. The process intensified as populations grew. There were goats, there was grazing, and there was a lot of erosion and fertility loss in the soil. By fertility loss, I mean those nutrients—nitrogen, potassium, phosphorus, all the various micronutrients, boron and so forth—tended to leach out or get used up by the animal grazers or by people.

So within 2,000 years, there were whole villages in Jordan that were abandoned because they couldn't support their farmers.

Soil fertility is nitrogen and other nutrients that are made available by soil microbes, and it tends to fall with overuse.

In the floodplain between the Tigris and Euphrates rivers, people started to build canals for irrigation 7,000 years ago in what's now called Mesopotamia. There were eight cities in the southern Mesopotamian region of Sumer 5,000 years ago. Uruk, a typical city in that region, had about 50,000 people, so these were pretty big cities.

Now the problem that they had was that the rains came in the spring, but they needed the water in the summer, so they had to dig canals and find ways to store water from spring through late summer. And this irrigation kept water on the surface and in the shallow ground water long enough for there to be a lot of evaporation, which tended to concentrate salts at the surface.

Now the usual solution for this would be to have less irrigation and more fallows or rest periods where the land can recover through natural processes in that high technology soil that we spoke about in the last episode.

But as populations rose, there was more irrigation and far fewer fallows. And so people ended up having to expand up into the hillsides for survival. And to do this they cut trees and started plowing the slopes. And when the rains came, they fell like tiny hammers on the bare soil, eroding it at many times the natural rate.

Sumer eventually silted up. Some of its original seaports are now 240 kilometers inland. The region, at its peak, held about 20 million people. This was about 4,000 years ago. But by then the soil had become so depleted that crop yields were down by a half. We know this from clay tablets that told about how the surface ran white with salt. Within 200 years of its peak population, it was a poor, conquered backwater.

Egypt fared far better in the Nile River Delta, which was settled about 7,000 years ago. Montgomery writes about two tributaries, the Blue Nile, which brought about a millimeter a year of silt with all of its mineral nutrients, and then the White Nile, which brought humus from African jungles every year. And so basically it brought topsoil and fertilizer to replace any possible agricultural mistakes. The water tended to flood in September, just in time for planting. All you had to do to make a good living there was to build dikes and flood them from the river when you needed them if the rains didn't come, and then just let it dry during the off season and let the water table retreat. This kept the salting down.

Egypt's agriculture lasted 7,000 years in the Nile Delta. Living was so easy that some have speculated, according to Montgomery, that the pyramids were essentially public works projects to curb unemployment.

Now archaeological studies have found settlements in Greece 7,000 years ago to 5,000 years ago, first in the valleys—and this was no problem because the soils actually grew under cultivation by the Greeks. But as populations grew, the Greeks started to move up into the hills and by 2,800 years ago, according to Hesiod, as quoted in Montgomery, the soils had become quite meager. There were thin rocky soils, and the hills around Athens became bare by 2,600 years ago. 2,400 years ago, Plato lamented the deforestation and how valleys were starting to fill up with silt. By 2,300 years ago, North African grain relieved Greek famines.

Now, Rome was founded in central Italy about 2,770 years ago. When it was founded, it was parceled into one hectare family estates that easily fed those living on them.

Within 240 years, the estates were up to two hectares in size, and they still comfortably fed a family. The ax and the plow saved labor, but they took twice as much land. Population, not surprisingly, increased. But now it was starting to press up into the hillsides. And once again, this led to a lot of erosion as people took to plowing straight up and down the hills. In many cases, this made the erosion up to 100 times faster than the natural rate. Sediment turned valley bottoms into malarial bogs by 2,200 years ago.

Now the Romans were students of the soil. They used manure, rotation, mineral supplements, but they hated to fallow their land. They liked to keep it productive at all times. And they loved the plow, which they used to aerate and dry the spring soils and kill weeds. As a market gardener, I can really understand this. Weeding is a hard, tedious chore.

Rome was already in trouble, but not all of its troubles were strictly due to population. Montgomery writes about how in the first century, Pliny of the Elder "attributed the decline of Roman agriculture to city dwelling landlords, leaving large tracts of farmland in the hands of overseers running slave labor. He also decried the general practice of growing cash crops for the highest profit to the exclusion of good husbandry. He maintained that such practices would ruin the empire." The issue is that overseers and slaves or tenant farmers care about maximizing this year's harvest either to avoid punishment or to get a quick bonus. But they don't really have a sense of long term value of the land. The overseers can easily move, and the slaves really can't be fired. Montgomery writes: "It is hardly surprising that even the best slaves generally do not exhibit initiative, care and skill. Instead, slaves generally want to maintain competence sufficient to avoid corporal punishment. They cannot be fired from their job and have no incentive to do it well. The very nature of servitude discourages creative expression or expertise at work."

Eventually, the land became so exhausted that it took 10 times as much land to feed a family by the time of Julius Caesar. In its waning days, Rome imported grain from northern Africa, Egypt and the Middle East. Eventually, when it crumbled, its fields in the north reverted to forest or to grass for up to nine centuries.

Eventually, there was a long run of good weather between the 12th and 14th centuries. Cultivated land in Europe expanded. The hilltops and hillside forests were cleared for farms. Europe's population grew to 80 million people and then, for many hundreds of years, was dogged by starvation, malnutrition, famine and pestilence. As you can imagine, many people living in these times made an intensive study and conducted many experiments in soil improvement.

The Netherlands, Denmark, England and France developed sustainable methods that we'll talk about in the next episode. These lead to much higher yields. But by the 17th century, according to Montgomery, real hunger launched Europe to the New World. During the ensuing Age of Exploration, a Dutch ship happened across a Pacific island, a good 1,600 kilometers from any other settled place in the world. The date was Easter Sunday, 1722, and the island, which the natives called Rapa Nui, appeared on maps as Easter Island.

Here was a treeless place filled with giant statues and stranded, starving cannibals. These were the sorry remnants of a fifth century Polynesian expedition that had settled the islands. Archaeological analysis of pollen in lake sediments revealed that there were extensive forests at the time of settlement. These were gone by the 17th century. Montgomery writes: "soil erosion accelerated once forest clearing laid the land bare. Crop yields began to fall."

Without the trees, they had no ability to make canoes or even fishing nets, so they just kept building statues.

Meanwhile, in the so called New World, multiple civilizations repeated the cycle. Maize, in other words corn, was domesticated 4,000 years ago in the Yucatán Peninsula. Before the rise of the Maya, forests had been cleared in patches in a classic slash and burn pattern, and villagers moved their fields every few years, which allowed the jungles to close in and the soils to regain their former fertility.

Gradually, though, cities grew. Tikal's cities were as big as Sumarian city states. They had no domesticated cattle, so no manure. And because they stayed in one location, at a certain point, their growth meant permanent cultivation surrounding the cities. Predictably, population pressure pushed people onto the valley bottoms and up the hillsides. By AD 800, the Mayan civilization peaked, and so did erosion. The Maya crumbled over the next 200 years. Montgomery writes: "when the food surpluses that sustained the social hierarchy disappeared, some Mayan cities were abandoned, with buildings half finished." Jungles covered up the cities until Lloyd Stephens rediscovered them in 1840.

Similar stories played out in Mexico, where 1,900 years ago, settlements in the Puebla Tlaxcala highlands were abandoned top to bottom—much as they were in ancient Greece. In New Mexico in Chako Canyon, the Pueblo arrived with maize 3,500 years ago. At the time, this area was a pinyon-juniper woodland. The pueblo cut the trees for shelter and fuel. Today it's a scrub desert.

Like the Mesopotamians, they were living in a rain-fed floodplain, and they had to irrigate their crops. This led to salinization, erosion, intense cultivation and weakened soils as the populations grew. 900 years ago, the region entered a two century long drought and was abandoned.

Now these are, of course, the cautionary stories. I'm saving the success stories for a future episode.

Modern Folly

But the question that we should be asking is: "did we modern people learn from these lessons?" I'll let you be the judge.

When Westerners arrived in the so-called New World, there were 4 to 10 million native North Americans. There were some 40-100 million native South and Central Americans at the time. And the Westerners found a landscape that maybe they didn't realize was actively managed, but not agricultural by nature. Well, they wasted no time in clearing the area for corn. Montgomery writes: "Intensive cultivation of corn quickly exhausted New England's nutrient poor glacial soils. Within decades, colonists began burning the forest to make ash fertilizer for their fields. With more people crowded into less space, New Englanders ran out of fresh farmland faster than their neighbors in the south. Early travelers complained about the stench from fields where farmers used salmon as fertilizer. And in the south, tobacco dominated the slave based economies of Virginia and Maryland, and soil exhaustion dominated the economics of tobacco cultivation. Once individual family farms coalesced into slave-worked tobacco plantations, the region became trapped in an insatiable socioeconomic system that fed on fresh land."

Tobacco was six times more profitable than any other crop at that time. It arguably saved the previously starving Jamestown colony by 1619. The problem is that it leaves the soil exposed, and it uses 10 times as much nitrogen and 30 times as much phosphorus as most food crops. Montgomery writes: "So Virginians grew just enough food for their families and devoted their energy to growing tobacco for European markets." It took just five years to wipe out the soil fertility growing tobacco in this manner. When bare soil and erosion leaves your homestead completely bare, what's a person to do? Move inland.

Montgomery quotes Thomas Jefferson as writing: "The indifferent state of agriculture among us does not proceed from a want of knowledge merely. It is from our having such quantities of land to waste as we please. In Europe, the object is to make the most of their land, labor being abundant. Here it is to make the most of our labor, land being abundant."

Montgomery quotes a settler named John Craven, who wrote about what he saw around the year 1800 when he arrived. John Craven says: "At that time, the whole face of the country presented a scene of desolation that baffles description. Farm after farm had been worn out and washed and gullied so that scarcely an acre could be found in a place fit for cultivation. The whole of the virgin soil was washed and carried off from the ridges into the valleys." The growth of plantation agriculture with slave labor growing tobacco was a perfect storm of soil destruction and established a legacy of poverty, especially in the South.

Now going back to the Old World in the same time period, even in Egypt, the indestructible Nile River Delta came under threat in the early 1800s when Egypt decided to become competitive as a cotton grower. Maybe you've heard of Egyptian cotton. This led to year round irrigation and the predictable result: salt deposits.

Now we haven't talked about China yet, so let's do that now. China's Yellow River used to meander across a vast floodplain until about 2,360 years ago, when the first dikes and levees were built there. Now, unfortunately, as people increased their farming activities in the Loess Plateau, which was the source of the yellow river, erosion and silt increased downstream, and this made the river harder to control.

So imagine yourself living in this flood plain, building these dikes, just basically building these walls of soil intended to hold the river in a particular direction. And the dikes get up to one meter, two meters, three meters, eventually 10 meters tall, and sometimes the river floods right up to the edges of the dike and you're going, "Uh-oh. Boy, I sure hope it doesn't jump the dike." It must've been a very tense situation.

Unfortunately, in 1852, the river did jump its dike, and when it did, it was a colossal disaster. The resulting flood and famine killed two million people.

Let's talk about this Loess Plateau, which is the source of the Yellow River. Loess or as we call it here in the United States, loess, is a thick blanket of fine grained soil that is mainly a result of glacial till from the poles. It covers about 1/10 of the land on the earth. It's mainly silt with a little bit of clay, and it's very mineral rich. Now, it doesn't stay put. It tends to pile up in windblown deposits. And today these are found in Argentina, Central Asia, Tajikistan, Kazakhstan, in China, New Zealand, in Europe, south of England, north of France, Germany, Poland, Ukraine. And here in the United States you'll find it along the Mississippi River, plus Nebraska, Kansas, Indiana, Ohio and the Dakotas.

Now the little secret about loess is that it's the best agricultural soil on the planet—if you treat it well. Fortunately, nature had done this in the high plains of the United States. There's evidence that the short grass sod in the High Plains was manured by Buffalo for 200-250 thousand years. When settlers arrived, they found that their plows couldn't cut through the thick roots of this turf. That is, until 1838, when John Deere introduced an unstoppable steel plow. Combined with Cyrus McCormic's mechanized harvester, settlers found that they could liberate the fertility of 15 times more land per person than any prior farmers could. Now, farmers were limited only by their ability to attract capital and investors.

Now do you see a problem here? This is very fine-grained soil in a high, dry, windy land, and it's held together by the roots of this sod—which suddenly settlers are able to cut through with a steel plow.

The U.S. Geological Survey saw trouble brewing as early as 1902, and said in its 22nd annual report that the High Plains are essentially held together by sod. They recommended that the region be used perhaps for grazing, but never tilling.

By 1928, the United States as a whole was losing soil ten times faster than it formed. On November 11th, 1933, McCormick writes, "The first major windstorm swept through South Dakota. Some farms lost all their topsoil in a single day. The next morning, the sky remained dark until noon: one part air to three parts dust."

This was followed by storms in 1934-5 that darkened skies and dumped dust as far away as Chicago and New York City. Montgomery writes: "On April 2nd, 1935, Hugh Bennett testified before the Senate Public Lands Committee about the need for a national soil conservation program. Bennett knew that a great dust storm from the Plains was descending on Washington. With help from field agents, who called to report the progress of the dirt cloud, he timed his testimony so that the sky went dark as he presented it. Duly impressed, Congress appointed Bennett head of a new soil conservation service."

The Erosion Research station in Tyler, Texas recorded soil loss events 200 to 800 times the natural rate. From Ohio to Oklahoma, cotton cultivation increased soil loss 10,000 times the natural rate.

Now, lest you think that this was strictly a problem that we faced in Western society, the Soviet Union's first 5-year plan in 1929 committed the Russian steppe to factory farming. This was expanded in the 1950s and 60s for cotton growing, and it led to a Dust Bowl in the Caspian Sea in 1969 that blew Russian soils all the way to Poland. Another storm in 1984 blew Russian soils all the way to France.

Seeking cotton independence, Russia built some 600 dams and thousands of kilometers of canals to divert water from the Aral Sea, which, as you might imagine, dried out. By the 1990s, Dust Bowls dropped salt and silt on Russian farms 1,600 kilometers away, and the Aral region emptied out.

Modernization did little for the West African Sahel, where nomad herds had grazed crop stubble and manured the fields for generations. The French colonial cotton plantations and ranchers reduced fallow periods, introduced new taxes and broke up the land in political boundaries that interrupted the migrations of the nomads and their herds. In 1972, there was a drought that killed 100,000 people in the region and without the manure from the nomads' herds, the topsoil loss proved irreversible. No plants to hold the soil, so the soil blew out. No soil for plants to grow, and so that was it.

In 1964 Egypt dammed the Nile, ending a 7,000 year run of natural fertility. Once the dam was in place, the resulting lake lost 14 cubic kilometers of water to evaporation every year that would have otherwise proceeded downstream to irrigate and fertilize the region. With all the silt being dumped into the lake, the delta has started to erode. Constant irrigation again for cotton salts the fields, and the area is now dependent on heavy fertilizer to make up for lost humus and minerals.

Now the so-called Green Revolution focuses on fertilizers to prop up fertility as the soils literally die. This masks the underlying problem of erosion and physical soil loss. Moreover, unlike the ultra high technology of living soil, the green revolution depends on just a very small number of chemicals that are mostly fossil in nature. These are guano, and nitrates, which are produced in energy intensive and hence oil intensive processes. Since the 1980s, India's agricultural output per ton of fertilizer has fallen by 2/3 according to Montgomery. In the same time frame, West Java's fertilizer and pest costs ate up all of their profits. Asia's fertilizer use has increased by 3 to 40 times, and according to a U.S. Department of Agriculture report from 1981, the United States lost more soil in the 1970s than it did during the Dust Bowl of the 1930s.

Status Today

Where does that leave us today? Right now, we farm a tenth of the planet and graze or pasture another 25%. Montgomery writes: "Globally, average soil cropland erosion of 10 to 100 tons per hectare per year removes soil about 10 to 100 times faster than it forms." He further adds "Across the planet, moderate to extreme soil erosion has degraded 1.2 billion hectares of agricultural land since 1945: an area the size of China and India combined."

Stop and think about that a moment. We're basically doing on a global scale what Rome did when it was on its way out. And we've lost in a single lifetime, as much soil as the entire area of the two most populous nations on Earth.

The way we do agriculture has other consequences as well. According to Montgomery, 30% of oil use is agricultural. A third of the carbon dioxide buildup in the atmosphere is due to degradation of soil organic matter. In other words, mistreating the soil is a major contributor to climate change.

Civilizations have a lifespan which is equal to the top soil depth divided by the net rate of loss. Given that we're now losing soil hundreds of times faster than we should be, the end is in sight.

Design Takeaways

What are our takeaways as designers from this morbid history?

Well, first of all, it should be clear that as much as possible, we want to avoid bare soils. Another thing we need to do is stay off the hills as much as possible: the hilltops and the steep slopes. That's just been a constant through history and across the world that when people start farming those areas, they massively increase erosion. We need to work on contour (I'll get into that in the next episode: this was something that the Romans didn't attend to and that many New World farmers failed to do properly). We need to do everything we can to restore nutrients with fallows, rotations and manure. We need to work at appropriate scale, neither too large, as in the case of large plantations with slave labor or with huge machinery that, like slavery, is not sensitive to the nuances of the land or the long term needs of the soil. But we also need to avoid working too small, because vulnerable populations have, throughout history and across the world, been forced to retreat into the hills and desperately carve out a living to the destruction of all. And more than anything, local ownership and control at the appropriate scale is something that we need to design into our future civilizations.

Close [music]

Please join me in the next episode for the thrilling conclusion to the soil saga. We'll take the takeaways and cautionary tales from today, plus all of the success stories that I left out of today (there's quite a few of them) and modern research and results, to build a resilient soil building strategy for Edenicity.

If you enjoyed Episode 14, please be sure to subscribe so you don't miss a show. If you haven't already done so, please visit the news link at to download a copy of the Reference Design (you'll need that for the next episode). Until next time. I'm Kev Polk, and this has been Edenicity.


David R. Montgomery, Dirt: The Erosion of Civilizations. University of California Press (Berkeley and Los Angeles: 2007).

Edenicity 14: Losing Soil

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