For hundreds of years, it wasn't uncommon for farmers in Europe to till their land and plant their crops only to see the soil wash away by year's end. Before they started all over again, many had to carry the lost soil back up to the fields. Piles of dirt overflowed oxcarts or burdened the farmers' backs as they made their way up the eroding hill.1 This Sisyphean effort was not unique to Europe; in the days of Mao, near-starving villagers in China's Loess Plateau worked day and night clearing land and cutting terraces into hillsides, planting every available acre with much-needed food crops. To their dismay, the terrace walls, made of the silty soil characteristic of the plateau, repeatedly crumbled, demanding rebuilding. Or the rains would come, sweeping the soil's precious nutrients and organic matter away. When harvests plummeted, farmers had little choice but to clear more land and expose more soil to rapid erosion.
Inevitably, there is no land left to clear. Even though most of the soil lost from hillsides is redeposited into floodplains and alluvial valleys, erosion takes agricultural uplands out of production, entombing soils into smaller and smaller cultivable areas. In the South Pacific, battles broke out over access to arable land after farmers stripped the soil from most of the Polynesian island of Mangaia.2,3
It's no wonder that some see the start of agriculture, about 10,000 years ago, as our fall from grace: when humans settled down and began domesticating animals and plants, they developed warfare, suffered increased malnutrition, and contracted new diseases such as smallpox and plague.4 For much of this time, humans worked the alluvial soils of fertile river basins: the Yellow River, the Indus, the Tigris, and the Euphrates. But around 4,000 years ago, people began ascending forested slopes and exposing virgin soils to seasonal rains. Manure was an early remedy for the loss of soil nutrients. The use of excrement from livestock is mentioned in many ancient texts. In recounting Odysseus's adventures with Cyclops, Circe, and Calypso, Homer pauses briefly to mention the use of manure. On returning to Ithaca in disguise, Odysseus is recognized by one of his old hunting dogs lying atop piles of dung soon to be spread on nearby fields. The ancient hound pricks up his ears, wags his tail in recognition of his owner, then dies. In seventeenth-century Tokyo, excrement was so valuable that toilets that emptied into streams were banned. There were costs to this technique: cultures steeped in manure had higher rates of infectious disease.5
There are other ways to beat depletion. Without any understanding of the nitrogen cycle, farmers have long practiced crop rotations with legumes: beans in the Americas, peanuts in Africa, soybeans in East Asia. These nitrogen fixers made cities and civilization possible.5 A major breakthrough occurred in 1913, when German chemist Fritz Haber discovered a way to synthesize ammonia from air. With the advent of nitrogen fertilizers, the job of rejuvenating the soil seemed to get easier. When nutrients washed away, there was no need to traverse the hills: a farmer could simply order up some more anhydrous ammonia. We now fix about 160 million metric tons of nitrogen each year, mostly in ammonia factories.6 There are costs to the widespread use of industrial fertilizers: phytoplankton bloom on these nutrients when they're washed to coastal areas, bacteria thrive on the organic material, and the resulting depletion of oxygen kills crabs, fish, and other sea life.7
The negative effects of our present system—soil erosion, chemical contamination, fossil-fuel use, and dead zones—are global problems. According to the Millennium Ecosystem Assessment, agriculture is the largest threat to biodiversity and ecosystem function of any single human activity.8 This is the agriculture of the plow, of the monoculture, of the annual—farming practices that tend to use and pollute more water, store less carbon, emit more greenhouse gases, and support less biodiversity than the ecosystems they replace.8 In the last 200 years, the United States has lost about 30 percent of its agricultural land to soil erosion—erosion that strips the soil of its nutrients and organic matter.9 It reduces soil depth and crop productivity. Every year, each hectare of U.S. cropland loses an average of 10 tons of soil to water and wind erosion, a rate that is about 10 times faster than the soil formation rate. This erosion costs the United States roughly $38 billion a year.10 In 2008, rainstorms in the Midwest caused extensive erosion: 200-foot gullies carved through the grain lands of Iowa. Downstream, a dead zone the size of Connecticut hugs the coast of Louisiana. Phytoplankton blooms, caused by the runoff of nitrogen fertilizers and other nutrients from upstream farms in the Mississippi Valley, deplete oxygen in the water column and along the ocean floor, leading to the death of marine life. The release of these nutrients is especially high from the farming states of Illinois, Iowa, Indiana, Missouri, and Arkansas, where corn and soybean agriculture is common.11
When it is used and abused, soil becomes a nonrenewable resource, like fossil fuels. But there's no Big Soil, with friends and lobbyists on Capitol Hill. So how do we turn this around? Many farmers and scientists tend to look at the problem through a contemporary lens:12 How can we breed better annuals, plants that have to be reseeded year after year? How can we produce less destructive monocultures? Can we eat closer to home? Efforts to eat local are laudable, but they won't solve the crisis: if most of the calories New Yorkers consumed were grown on the relatively thin soils of the state, there would be few trees left and much-degraded land. For the foreseeable future, the bulk of the food consumed by Northeasterners will come directly or indirectly from grain crops grown in the Midwest and Great Plains. We need to take the longer view, restoring ecological health to agricultural landscapes and supporting the economic and cultural stability of rural communities. But how do we get there?
All of nature's ecosystems feature perennials grown in mixtures. More than 85 percent of North America's native plant species are perennials, plants with deep root systems, capable of staying in the ground year after year.13 These species mixtures build soil and offer a host of ecosystem services, including maintaining water quality, providing wildlife habitat, and sequestering carbon.14
The Land Institute's 50-Year Farm Bill, as seen in the Solutions feature article by Wes Jackson, calls for a profound transition in U.S. agriculture, from the current system dependent on soil-eroding annual monocultures to one reliant on soil-building perennial polycultures. This plan will not only save our soils, but it will help alleviate climate change, create jobs, and improve water quality for all people—in 2001, it was estimated that approximately 40 percent of the U.S. freshwater supply was unfit for recreational or drinking purposes because of contamination from agricultural runoff and erosion.10 Perennials, with their deep roots and reduced fertilizer needs, are carbon sinks, outsequestering conventional farms with annual monocultures. By reducing the use of fertilizers, we will stop fueling our ocean's dead zones. And because perennials will require more eyes per acre—more people working the land—we will be creating jobs for farmers across the nation. Agriculture offers an excellent opportunity to demonstrate large-scale transformation toward sustainability. The proof of this renewal will be in the soil itself.
The Worldwatch Institute's Mitigating Climate Change through Food and Land Use emphasizes agriculture's potential to help reduce greenhouse gas emissions and proposes strategies to make farming more sustainable.15 While the land-use sector has long been one of the most significant contributors to climate change—more than 30 percent of all greenhouse gas emissions are a result of agriculture, forestry, and other land uses—terrestrial carbon sequestration offers what is likely to be our greatest possibility for large-scale removal of greenhouse gases from our atmosphere. Soil and plants hold three times as much carbon as does the atmosphere; recognizing and protecting this tremendous carbon sink—and reinforcing it with the help of perennial crops—would be a great step toward a more sustainable world.
The authors of the Worldwatch report suggest five major strategies for reducing and sequestering terrestrial greenhouse gas emissions:
- Farming with perennials.
- Enriching soil carbon, with alternative practices such as no-till agriculture.
- Producing climate-friendly livestock, with practices such as rotational grazing systems, manure management, methane capture for biogas production, and improved feeds and feed additives. Corn agriculture currently occupies about 80 million acres in the United States, a chunk of land almost the size of California. At least half of that acreage is used to grow corn to feed livestock. Returning cows to a grass diet, fed largely by perennials, will revolutionize farming, shrinking the carbon footprint, decreasing the need for chemical fertilizers, and promoting more humane farming practices.
- Restoring degraded watersheds and rangelands—a win-win strategy for addressing climate change, rural poverty, and water scarcity.
- Protecting natural habitat. A shift to perennial agriculture must be accompanied by increased protection of existing wild spaces. The nearly 10 billion acres of forests and 12.4 billion acres of natural grasslands are a massive reservoir of carbon, removing carbon from the atmosphere as they grow. Deforestation, grassland and forest fires, and land clearing are major sources of greenhouse gas emissions. Incentives, such as product certification and payments to protect habitats and sequester carbon, will be essential to encourage farmers and land users to maintain natural vegetation.
Agricultural changes can be profitable and sustainable, with a great potential for large-scale adoption, impact, and permanence. Perennial agriculture can reduce emissions through less aggressive tillage and controlled use of nitrogen fertilizers. Animal agriculture can capture and flare methane from dairies and feedlots and look for opportunities to aggressively use a pasture base for production. Agriculture also has the greatest influence on the second-largest carbon sink on the planet, the Earth's soils. Farmers manage soil on a daily basis. Continuous payments to farmers can be reserved for protecting and restoring natural areas.
As the 50-Year Farm Bill shows, we have the opportunity to take one of the most important steps in our approach to food and land use since we first started down the road to agriculture 10,000 years ago, stopping the deficit spending of ecological capital that has been the norm for millennia. There is no time, and no more soil, to lose. As one of us (Wes Jackson), recently told a congressional aide, "Salvation doesn't come at any old time, you know."
- Lowdermilk, WC. Conquest of the land through seven thousand years. Agricultural Information Bulletin 99, 1–30 (1953).
- Kirch, PV. Microcosmic histories: Island perspectives on "global" change. American Anthropologist 99, 30–42 (1997).
- Montgomery, DR. Soil erosion and agricultural sustainability. Proceedings of the National Academy of Sciences 104, 13268–13272 (2007).
- Larsen, CS. Biological changes in human populations with agriculture. Annual Review of Anthropology 24, 185–213 (1995).
- McNeill, JR & Winiwarter, V. Breaking the sod: Humankind, history, and soil. Science 304, 1627–1629 (2004).
- Socolow, RH. Nitrogen management and the future of food: Lessons from the management of energy and carbon. Proceedings of the National Academy of Sciences 96, 6001–6008 (1999).
- Rabalais NN, Turner, RE & Scavia, D. Beyond science into policy: Gulf of Mexico hypoxia and the Mississippi River. BioScience 52, 129–142 (2002).
- Cassman, KG & Wood, S. Cultivated systems. In Ecosystems and Human Well-being 745–794 (Island Press, Washington DC, 2005).
- Pimentel, D et al. Environmental and economic costs of soil erosion and conservation benefits. Science 267, 1117–1123 (1995).
- Pimentel, D & Pimentel, M. Food, Energy, and Society 3rd edn (CRC Press, Boca Raton, FL, 2008).
- Alexander, RB et al. Differences in phosphorus and nitrogen delivery to the Gulf of Mexico from the Mississippi River Basin. Environmental Science and Technology 42, 822–830 (2007).
- Glover, J et al. Future farming: A return to roots? Scientific American Magazine 297, 82–89 (2007).
- Chiras, DD & Reganold, JP. Natural Resource Conservation: Management for a Sustainable Future 9th edn (Prentice Hall, Upper Saddle River, NJ, 2004).
- Jordan, N et al. Sustainable development of the agricultural bio-economy. Science 316, 1570–1571 (2007).
- Scherr, SJ & Sthapit, S. Mitigating Climate Change through Food and Land Use (Worldwatch Institute, 2009).