Dennis Zeedyk-Dirt: The Erosion of Civilizations 

Book Report by Dennis Zeedyk 

Title: Dirt: The Erosion of Civilizations 

Author: David Montgomery 

Publication: 2008 

Pages: 246 

Completion: 5/28/25 

Why I read this book: A friend & fellow agricultural economist from The Ohio State University sent me a copy of this book. Given my farm background and agronomy minor, coupled with my love of history, made this a very interesting book to read. 

What I learned from this book: 

1. While the world’s population keeps growing, the amount of productive farmland began declining in the 1970’s and the supply of cheap fossil fuels used to make synthetic fertilizers will run out later this century. I am not sure I agree entirely with this. Crude oil is currently at $60/barrel. I don’t think the author has taken into consideration the full effects of the shale oil revolution & fracking. New technology may allow for some crops like corn to begin fixing nitrogen, reducing the need for nitrogen fertilizers (but not phosphorus, potash or micronutrients). Also, there is negative population growth in all European and many Asian countries, as well as in North America. 
2. The history of life is inextricably related to the history of soil. 
3. Billions of microscopic bugs can live in a handful of topsoil. Those in a pound of fertile dirt outnumber the Earth’s human population. 
4. An impressive array of physical & chemical processes help build soil. Burrowing animals like gophers, termites & ant mix broken rock into the soil. Roots pry rocks apart. Big rocks break into little mineral grains from wetting & drying, freezing & thawing or heating by wildfires. 
5. Climate strongly influences soil formation. Temperature & rainfall control the plant communities that characterize different ecosystems. 
6. There are ~20,000 specific soil types recognized in the U.S. 
7. Proportionally, Earth’s skin (soil) is much thinner and more fragile than human skin is to people. 
8. You can see evidence of soil erosion downstream along the major rivers, where ports become inland towns as sediments derived from soil stripped off hillsides further upstream pushed the land seaward. 
9. Agriculture developed independently in: 
10. Mesopotamia 
11. People here were forced into labor intensive agriculture due to a small Ice Age (Younger Drya) in 10,000 B.C. that affected their ability to hunt & gather.
12. They began cultivating wild rice & wheat that survived the transition to a colder, more arid climate. Soon barley & peas were added to the mix.
13. Most farm animals were domesticated from 10,000 to 6,000 B.C. Sheep & goats were domesticated in 8,000 B.C. & cattle in 6,000 B.C. Domesticated livestock helped with the labor needed to produce harvests, but also added manure to help replenish soil nutrients. There were “4 million people on Earth at this time. As agricultural societies developed, humanity began doubling every thousand years, reaching 200 million by the time of Christ. 
14. All the good fertile land in Mesopotamia was being farmed by 4500 B.C. It was being irrigated to maximize output. As the water evaporated, it left behind salts. Salinization began affecting early societies.
15. Extensive erosion from the upland hills filled the Tigris & Euphrates Rivers. Once a thriving seaport, ruins of Abraham’s hometown of Ur now stands 150 miles inland.
16. Egypt 
17. The floodplain of the Nile proved ideal for sustained agriculture. The difference is that the Nile’s life-giving flood reliably brought little salt and a lot of fresh silt to fields along the river each year.
18. In 1964, the Aswan dam across the Nile brought the above to an end. Under the desert sun, six feet of water evaporate off the top of the lake each year. The even greater problem is that the 130 million tons of dirt that the Nile carried off from Ethiopia settled out in the bottom of Lake Nasser and no longer replenished the land of Egypt along the Nile.
19. Salinization is an issue for Egypt, reducing crop yields on 10% of the fields in the Nile delta.
20. Northern China 
21. Chinese people overwhelmingly live on the alluvial plains where great rivers descending from the Tibetan Plateau deposit much of their load of silt. Flooding has been a problem for thousands of years on the Huanghe (Yellow River). It is called the Yellow River because of the color of dirt eroded from the river’s deforested headlands. 
22. In 340 BC, levees & dikes were constructed to protect the people in the floodplain. When the river hit the plains, it would drop its silt load between the levees instead of in the floodplain. The people continuously rebuilt the levees ever higher to contain the floodwaters ensured the riverbed climbed above the alluvial plain about a foot per century. By the 1920’s, the surface of the river towered 30 feet above the floodplain during high-water season. This guaranteed that any flood that breached the levees was devastating.
23. Today the cradle of Chinese civilization is an impoverished backwater lacking fertile topsoil, much like Mesopotamia. 
24. Central America 
25. The first Central American communities grew to regional prominence after maize was domesticated around 2,000 B.C.
26. Mayan farmers terraced hillsides to create flat planting surfaces, slow erosion and divert water to fields. Where these terraces remained intact, they held 3-4 times more soil that lied on adjacent cultivated slopes. 
27. In other parts of Central America, there was no soil conservation efforts & sedimentation into lakebeds increased substantially from 250 BC to 900 AD. While not necessarily responsible for the collapse of the Mayan civilization, soil erosion peaked shortly before it unraveled when the food surpluses that sustained the social hierarchy disappeared. 
28. Modern farmers in Peru’s Colca Valley still use ancient terraces cultivated for more than 15 centuries. They also do not till the soil, but insert seeds into the ground using a chisel-like device that minimally disturbs the soil. These long-cultivated soils have A horizons that are typically 3-4 feet thicker than neighboring uncultivated soils and are full of earthworms with higher concentrations of C, N & K. 

2. Even Plato & Aristotle recognized signs that land use like extensive tilling & grazing on hillsides had degraded their region’s soils. They may not have known about the fertilizing properties of manure. 
3. In the 3rd century B.C., North Africa faced constant pressure to produce as much grain as possible to feed the Roman Empire. The Libyan coast produced copious harvests until soil erosion so degraded the land that the desert began encroaching from the south. 
4. European Agriculture. 
5. England’s cereal production & population both doubled between 1750 & 1850. 
6. At the start of the 1800’s, most Europeans survived on 2,000 calories per day or less, below the average for Latin America & North Africa today. 
7. The eruption of Indonesia’s Tomboro volcano in 1815 caused the coldest summer on record, producing catastrophic crop failures in Europe. A potato blight in Ireland in 1844-45 showed how insecure food production had become. About 1 million people died of starvation and another million emigrated, with another 3 million emigrating over the next 50 years. 
8. Relatively few people from northwest Europe left for America until late 1800’s when fertile land became more difficult to obtain. One reason the Dutch started taking land from the sea is that they were surrounded by powerful neighbors and could not expand that way. 
9. Europe solved its perennial hunger problem by importing food & exporting people. About 50 million people left Europe during the wave of emigration between 1830 & 1930. 

13) American Agriculture. 

1. Initially, frontier communities generally exhausted their soil because of the economic imperative to grow the highest value cash crop, which was tobacco starting in about 1617. Within a century, annual exports of tobacco to Britain soared a thousand-fold to more than 20 million lbs. Despite its toll on the land, tobacco fetched more than six times the price of any other crop and could survive the long journey across the Atlantic. In 1677, the royal treasury pocketed 100,000 British pounds from import duties on Virginian tobacco & another 50,000 from Maryland. Virginia returned more to the royal pocketbook than any other colony; more than four times the revenue from the East Indies. Tobacco reigned supreme as the undisputed king of the southern colonies. Meanwhile there appeared to be general ignorance towards the use of manure as a fertilizer. It was cheaper to buy newly cleared land than to care for existing land. 
2. New land was constantly being cleared and old land abandoned because a farmer could only count on 3-4 highly profitable tobacco crops from newly cleared land. Tobacco strips more than ten times the nitrogen and thirty times the phosphorus from the soil than typical food crops. 
3. Cotton & tobacco dominated agriculture so much that before the Civil War the South was a net importer of grains, vegetables and farm animals. 
4. In a way, the intensity of soil erosion helped trigger the Civil War. Tobacco & cotton monoculture required slavery to turn a profit – it was critical to the export-oriented, cash-crop monoculture common throughout the South. Involuntary labor rarely produces quality results as even the best slaves generally do not exhibit initiative, care and skill. Slavery was consistently moving west as southeastern soils were exhausted. If slavery was banned in the West (as proposed the government), slaves would lose their value, wiping out half the South’s wealth. Lincoln’s election threatened slave owners with financial ruin.
5. The immediate causes of soil exhaustion in the antebellum South were well-known. There was continuous planting without crop rotation, inadequate provision for livestock to provide manure and tilling hillsides straight up and down, leaving bare soil exposed to rainfall and erosion. By the early 1900’s, more than 5 million acres of formerly cultivated land in the South lay idle because of the detrimental effects of soil erosion.
6. In the early 1900’s, the US Geological Survey concluded that the semi-arid High Plains from Nebraska to Texas were fatally vulnerable to rapid erosion if plowed. The first major windstorm of 1933 swept through South Dakota on November 11th. Some farms lost all of their topsoil in a single day. In May 1934, fields from Montana & Wyoming were ripped up by high winds. In spring of 1935, strong winds tore through parched fields of KS, TX, CO, OK & NE. With the fields freshly plowed, there was no vegetation to hold the soil in place. This erosion was partly responsible for the loss of US farms during the 30’s. 
7. New England’s agriculture was more diversified from the start because no lucrative export crops grew there. 

14) Desertification

1. Erosion rates of 2-3/4 inches of soil per year are reported in semiarid regions of North Africa once the native perennials are gone.
2. More than a tenth of Earth’s land is desertifying – about 1/3 of the planet’s dry lands. 
3. Before WWII, Western Europe was the world’s only grain importing region with North America, Latin America, Eastern Europe and Africa all exporting or being self-sufficient. Today, North America, Australian and New Zealand are the only major grain exporters. I disagree with this statement as there are significant exports from Argentina & Eastern Europe as well. 
4. Across the planet, moderate to extreme soil erosion has degraded 1.2 billion hectares of land since 1945. Average cropland erosion of 10-100 tons/hectare removes soil faster than it can form. 

15) Progress

1. Improvements in equipment, crop rotations, and land drainage doubled both European and Chinese crop yields between the 13th & 19th centuries. 
2. The development of nitrogen & phosphate fertilizers in 1843 allowed for increased crop yields. 
3. Guano (bird poop) was exported from Peru in starting in the 1850’s, peaking in 1856 and completely gone by 1870. This was used as fertilizer in the US and other countries. 
4. In the US, the National Defense Act dammed the Tennessee River at Muscle Shoals, AL to generate cheap electricity to produce synthetic nitrogen fertilizer or munitions- whichever was in greater demand. One plant was operating when Japan bombed Pearl Harbor; ten were in operation by 1945. The International Fertilizer Development Center is based in Muscle Shoals.
5. Global production of ammonia more than doubled in the 1960’s and doubled again in the 1970’s. Natural gas remains the principle feedstock for about 80% of global ammonia production. Global use of nitrogen fertilizers tripled between WWII and 1960, tripled again by 1970 and doubled again by 1980. From 1961-2000, there is an almost perfect correlation between global fertilizer use and global grain production.
6. Much of the increased demand for nitrogen fertilizer reflects the adoption of new high-yield strains of wheat & rice developed to feed the world’s growing population – known as the Green Revolution (GR). GR crops now account for more than 34’s of the rice grown in Asia. Almost half of third-world farmers use GR seeds, which doubled the yield per unit of nitrogen fertilizer. 
7. Per capita food production since the 1960’s has increased faster than the world’s population. World hunger persists because of unequal access to food, a social problem of distribution & economics rather than inadequate capacity. At present, agriculture consumes 30% of our oil use. As oil supplies dwindle, oil & gas become too valuable for fertilizer production. I disagree with this statement for multiple reasons. First, because of the shale revolution, we have plenty of foreseeable cheap oil & gas. Secondly, technology keeps increasing food production, especially now that the world population growth is slowing and thirdly, if oil & gas are too expensive for fertilizer production, which means it is by default too expensive for food production and nothing is too expensive when it comes to not starving to death. Lastly, many of the crops currently going towards biofuels can be transitioned directly to food crops if relative prices of food vs. fuel changes in a positive direction (e.g. growing sweet corn instead of feed corn). 
8. Recent USDA estimates show soil erosion from U.S. cropland as dropping from 3 billion tons in 1982 to under 2 billion tons in 2001. Contour tillage, cover crops, no-tillage and crop rotations are all helping to arrest soil erosion. 
9. Retaining soil organic matter is the key to sustaining high intensity farming. Organic matter helps retain moisture, improve soil structure, helps liberate nutrients from clays and is itself a source of plant nutrients. Soil is an ecological system in which microbes provide a living bridge between soil humus and living plants.
10. US farmers are becoming world leaders in soil conservation. No-till captures the benefits of plowing without leaving soils bare and vulnerable to erosion. In the 1960’s, almost all land was plowed, but over the past 30 years adoption of no-till methods has grown rapidly. No-till reduces soil erosion by 90-98% and can increase organic matter content of the top few inches by 1% per decade.

CONCLUSIONS (with Dennis Zeedyk’s thoughts in italics) 

1. As long as soil erosion continues to exceed soil production, it is only a matter of time before agriculture fails to support a growing population. Erosion rates in the US are already falling & government incentives promote filter strips, cover crops & no-tillage to reduce erosion. 
2. Throughout history, societies grew & prospered as long as there was new land to plow or the soil remained productive. New land has not been brought into production in the US since probably the early 1900’s. All of the increase in production has come about from increased yields. The main country where new land has been planted is probably Brazil & even the rate of this is declining due to environmental concerns. 
3. Under the right circumstances any one, or any combination of political turmoil, climatic extremes, or resource abuse can bring down a society. Shifting climate patterns and depleted oil supplies collide with accelerated soil erosion and loss of farmland. Should world fertilizer or food production falter, political stability could hardly endure. The shale revolution will keep crude oil cheap for the foreseeable future, so the production of nitrogen & phosphorus should not be an issue. 
4. Agro-technology fixes become progressively more difficult to maintain as soil thins because crop yields decline exponentially with soil loss. Coupled with the inevitable end of fossil-fuel-derived fertilizers, the ongoing loss of cropland and soil poses the problem of feeding a growing population from a shrinking land base. The shale revolution should keep crude oil prices low to keep the production of nitrogen fertilizers going well into the future. GE crops may soon be able to fix their own nitrogen like legumes. World population growth is slowing and is negative in the US. 
5. Globally about 1.5 billion hectares are now in agriculture production. Feeding a doubled human population without further increasing crop yields would require doubling the area presently under cultivation. But we are already out of virgin land that could be brought into long-term production. Simply staying even in terms of food production will require major increases in per hectare crop yields, increases that may not be achievable despite human ingenuity. We are still waiting for the next innovation to crank up food production despite the reality that over the coming decades, further increases of more than 1% are needed to meet projected demand for wheat, rice & maize. Growth in crop yields has already slowed until the cost of research to bring even incremental increases in crop production has skyrocketed. There are multiple incorrect assumptions in the above paragraph. First, the world population is only growing at X%, primarily in Africa, Middle East and South Asia. Most of the increase in food production over the past century is because of increased yields & I don’t expect this to change. Secondly, what will change will be the mixture of crops produced. If maize & soybeans in the US ceased to go into biofuels and this land was converted to grow food like potatoes, edible beans, vegetables & fruits – there would be an almost incalculable increase in edible food available. Lastly, if food prices changed massively due to huge decreases in production, there would be a simultaneous change in consumption patterns. For example, less meat and more plant proteins might be consumed. Beef (which requires 5-10 times the amount of food to produce a kilo of meat) will be changed to chicken or farmed fish, which are much more efficient producers of protein.
6. We need to know how much soil it takes to support a person, and how far we can reduce that amount. The most intensively farmed areas use about 0.2 hectares to support a person. If the US changes the mixture of crop production away from corn & soybeans, more than enough edible food will be produced on an amount of land much greater than 0.2 hectares/person. 
7. Global reserves, the amount of grain stored on hand at any given time, fell from a little more than a year’s worth in 2000 to less than a quarter of annual consumption in 2002. This could be a short- term anomaly. Change over two years of global reserves is not enough to show a true trend. Trends over a longer period of time would be a better predictor of global reserves. Also, there can be some substitution between grains (less wheat & more rice) or change between types of wheat (red winter wheat vs. spring wheat vs durum wheat). 
8. We need a new agricultural model, a new farming philosophy. We need another agricultural revolution. We need to adapt what we do to where we do it. One option might be using the downstream end of modern sewage systems to close the loop on nutrient recycling by returning the waste from livestock & people back to the soil. There is a law in Ohio, and presumably other states, about the use of human sewage on direct food. It can go onto crops like soybeans or field corn that requires further processing or goes into animal feed. In any case, nearly all manure produced by livestock & a portion of human sewage in the US is returned to the land. It is not wasted.
9. A different approach is to promote the prosperity of small farms in developing countries, keeping more people on the land, practicing intensive organic agriculture on smaller farms, using technology but not high capitalization. We need to enable peasant farmers to feed themselves, and generate an income capable of lifting them out of poverty while making them stewards of the land through access to knowledge, the right tools, and enough land to both feed themselves and grow a marketable surplus. This is a lofty goal, but the large majority of surplus food will still come from large farms. It must because that is how people in the cities will be food.
10. Many factors may contribute to ending a civilization, but an adequate supply of fertile soil is necessary to sustain one. Using up the soil and moving on to new land will not be a viable option for future generations. This has not been an option (except in South America) for a long time. Future excess food growth will be as a result of new ag technology and changes in production of various food products (from biofuels to direct food) on existing or a slightly declining land base.