Dirt: The Erosion of Civilizations

  • David R. Montgomery
University of California Press: 2007. 295 pp. $24.95, £15.95 0520248708 | ISBN: 0-520-24870-8

If everyday expressions offer clues to what we value, then the common use of 'dirt-cheap' to describe anything inexpensive speaks poorly of our appreciation for soil. Like water andair, soil is not efficiently traded and priced in the marketplace, and yet we could not live without it. It doesn't take a rocket scientist to figure out that food security and human well-being depend on fertile soil. That expression implies admiration for the intelligence of rocket scientists, and similar praise is due to Earth scientist David Montgomery, whose new book insightfully chronicles the rise of agricultural technology and the concomitant fall of soil depth just about everywhere in the world, from prehistoric to modern times. The topic could not be more timely, as recent large-scale expansion of maize (corn) in the United States and sugar cane in Brazil for biofuel production signals a new era of competition between the energy and food sectors for the globally finite resource of arable land and the remaining good soil.

Dust in the wind: civilizations collapse when their soil runs out. Credit: B. FORSTER/GETTY IMAGES

Montgomery catalogues a tragically recurrent pattern. Starting with the first farmers in the Tigris and Euphrates River basins, across the Mediterranean of the ancient Greeks and Romans, through bronze, iron and industrial ages, repeated in the Americas and in Asia, and up to contemporary practices on industrial mega-farms and smallholder slash-and-burn fields. In each case, agriculture expanded on good land, which fuelled population growth, followed by further agricultural expansion onto marginal land, ultimately leading to soil erosion, declines in agricultural productivity, and often societal collapse and emigration.

Perhaps owing to the repetitive nature of this story, the writing is not as captivating as Jared Diamond's in Collapse (Viking, 2004), which similarly charts the interplay between the prosperity and longevity of civilizations and their husbandry of several kinds of inherited natural capital. Equally provocative, however, Montgomery asserts that the rise and fall of many civilizations, generally lasting from 800 to 2,000 years, roughly corresponds to how long it takes for their soils to erode away.

Not all is gloomy. A precious few examples of good soil management are described. Montgomery also cites philosophers, agronomists, and soil scientists from ancient Greece onwards, showing that we have known for a long time how to obtain good crop yields and simultaneously conserve soil. Reasons that such sage advice has seldom been followed include perverse economic incentives and land tenure laws, imposed by govenments that reward mining the soil for short-term profits. Montgomery offers a wealth of interesting examples.

The Lincoln Memorial in Washington DC now stands where colonial ships once sailed in the Potomac River and is built on the sediments washed downstream from former colonial tobacco farms. High prices paid for tobacco in Europe, a plentiful supply of cheap land in the American colonies, and tax revenue for the British government generated from tobacco sales motivated both private and government sectors to seek maximum crop yields rather than promote sound agricultural management. These shocking changes become obvious over many decades and centuries, but soil often slips away at a rate that a farmer may not perceive during a single lifetime.

Further advances in technology will probably increase crop productivity, and some expansion of agricultural land is still possible, but Montgomery argues that soil has become a scarce resource. More than a history lessonof the legacies of past civilizations, the book raises a critical concern for modern times. We are currently losing soil at least 20 times faster, on average, than it is being replaced through natural processes. To meet the demands for food and, more recently, energy, we need Montgomery's scholarly, historical perspective, as well as the ability to project current trends of land management to future scenarios.

In the final chapter, the author offers a vision of organic farming for both large and small farms. Soil conservation can also be promoted without going totally organic, and I doubt that we can feed 7–10 billion people entirely without fertilizers and pesticides. We probably need the proverbial cleverness of rocket scientists to figure out what sustainable agriculture fully entails, but it is clear that soil conservation must be its central tenet.

When I talk to elementary school classes about soil, I start by distinguishing it from dirt. Kids quickly catch on that soil nourishes plants in forests, grassland, farms, and gardens, whereas dirt is soil transported to places where it is unwanted, such as under fingernails, on the living room carpet and in sediments of reservoirs and estuaries. The greatest strength of this book is its persistent and forcefuldemonstration of a lesson that adult societies have yet to embrace — societies prosper and persist best when they figure out ways to keep their soil where it belongs and not treat it as if it were dirt cheap.