The most overlooked, yet most crucial, material that sustains life on earth is dirt—or to use the more technical term, soil. David R. Montgomery's Dirt: The Erosion of Civilizations presents a cultural history of the degradation of this vital resource and aims to show how soil exhaustion has shaped the course of human civilizations. Montgomery, a professor of earth and space sciences at the University of Washington, uses an approach similar to the one taken by Jared Diamond in Collapse (Dirt and Collapse even share some case histories: Easter Island, Hispaniola, and the Mayan empire). Montgomery looks at environmental failures of the past to deduce lessons about the future of societies.
The book documents how societies have overused soils despite depending on them for the provision of drinking water, the production of food, and a range of other environmental services. The author refers to a multitude of cultures, from the first agricultural civilizations in Mesopotamia to the Greek, Roman, and Mayan empires; to central European societies; and finally to colonial North America. (Sometimes the jumps between places and eras are quite sudden.) He identifies a common pattern in most of these societies: the development of agriculture in fertile valleys leads to a growing population, the rising food demands of a growing population trigger the farming of marginal land, these sensitive lands soon become eroded, and agricultural yields decrease. In the end, soil degradation predisposes civilizations to failure, unless societies are able to shift their unsustainable demands for agricultural land elsewhere: for example, central European states that had access to “fresh land” in their colonies overseas, and the United States, which step by step absorbed the wealth of previously undeveloped agricultural land in the American West.
The failure to maintain the thin organic layer between rocks and vegetation in the long run is not merely a problem of the past. The book reveals alarming figures: More than 10 percent of the world's land surface is affected by desertification, an area the size of China and India combined has been degraded by moderate to extreme soil erosion since 1945, and around 1 percent of the world's arable lands are lost every year. Montgomery attributes such land degradation to the use of heavy farm machinery and of agrochemicals—the fundamentals of modern industrial agriculture—pointing out that the discovery and large-scale supply of mineral fertilizers made nutrient provision from soils seem superfluous, which led to neglect of soil fertility, the segregation of crop production from animal husbandry, and the rise of large-scale monocultures. But by freeing agriculture from local soil conditions, the introduction of machinery, mineral fertilizer, and pesticides created a new dependency—on fossil fuels.
Some people consider advances in biotechnology, nanotechnology, and other technologies to be a pathway to sustainable farming (e.g., Lal 2007). Montgomery does not. He doubts the promises of greatly improved crop yields from genetic engineering, and points out the social and environmental risks. Nor does Montgomery consider hydroponics—the cultivation of food under conditions that allow full control of vegetative growth through the manipulation of water, light, and nutrients—a plausible option for feeding the world on a large scale.
Rather, he expressly proposes an array of low-tech solutions to restore soils, to make them fertile and rich in organic matter. The book calls for the application of sound agroecological principles, and especially for the use of locally adapted practices stemming from both traditional insights and knowledge and modern ecology. Two agroecological strategies that seem particularly promising are organic and no-till agriculture, both of which are designed to sustain soil fertility and indeed may offer solutions to at least some of the negative aspects of industrial farming. To reduce the dependency of food production on petroleum, the book further suggests an “unglobalization” of agriculture to be achieved by strengthening small, local markets. Montgomery emphasizes that every acre of agricultural land will be needed in the future and pleads for an end to the conversion of farmland to other uses, which is now a dominant feature of many parts of the world.
An unusual case history from Cuba demonstrates how necessity can promote alternative farming at the national scale, at least in a totalitarian state. Cuba faced a severe shortage of fossil fuels, fertilizer, and pesticides after the fall of the Soviet Union. The country had needed to double its food production while the supply of inputs required by conventional agriculture was halved. Cuba responded with the development of low-input and no-till farming methods, including traditional farming, organic agriculture, and small-scale urban agriculture. It thus became an unexpected experiment in how to scale up these techniques.
In my opinion, Montgomery's most important contribution is his critique of the worldwide homogenization of farming through large agribusinesses and his proposal that agricultural practices be adapted to local environmental conditions (and not vice versa). His narrative of environmental degradation throughout the history of civilizations appears too generalized over time and space and seems pessimistic to me. For example, Grove and Rackham (2001) conclude that the Mediterranean Basin— which Dirt describes as a case of environmental degradation—is far from being a “ruined landscape.” The long-lasting human impact on the Mediterranean landscapes, according to their account, has rather created resilient ecosystems with high species diversity, productivity, and utility to society. I wonder whether it wouldn't be more instructive to draw lessons from civilizations that succeeded in managing their environments than to focus just on societal collapses. Many cultures have developed agricultural systems that sustained agricultural productivity, conserved or improved soil fertility, and moreover supported a unique biodiversity over long periods of time—the parklands of Western Africa, the terraced olive groves of the Aegean, ancient agricultural systems in the Andes, and the home gardens of the Pacific Islands are but a few. These intensive, diversified, and permanent farming practices demonstrate that dense population and soil erosion do not have to be inevitably linked, as Montgomery suggests (compare, e.g., with Netting ).
Dirt is a mixture of disciplinary depth (focusing on soil geomorphology) and an impressive interdisciplinary breadth (combining aspects of archaeology, geology, and environmental sciences). The meaningful historical photographs and sketches are especially worth mentioning. The book uses accessible language, but it does not match the brilliant standard of Diamond's Collapse, and its structure is a bit difficult to grasp. However, all in all, the book offers fascinating insights into what may be our most precious natural resource and gives important pointers toward sustainable land management.