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Chapter 3. Signs of Stress: The Biological Base: Soils Eroding
After the earth was created, soil formed slowly over time from the weathering of rocks. It was this soil that supported early plant life on land. As plant life spread, the plants protected the soil from wind and water erosion, permitting it to accumulate and to support even more plant life. This symbiotic relationship facilitated an accumulation of topsoil until it could support a rich diversity not only of plants, but also of the animal life that depends on plants.
The thin mantle of topsoil, measured in inches over most of the earth, is the foundation of civilization. When earlier civilizations lost their productive topsoil from mismanagement and erosion, they crumbled as their food supply shrank. With an estimated 36 percent of the world's cropland now losing topsoil at a rate that is undermining its productivity, our food security is also at risk if this trend continues.50
As pressures to expand food production have climbed, farmers have been forced into marginal areas, plowing land that is too dry or too steeply sloping to sustain cultivation. At some point probably within the last century, the long-term accumulation of topsoil was reversed as erosion losses surpassed new soil formation, leading to a gradual depletion of this basic natural capital.
The United States, the world's breadbasket, has undergone two periods of extensive overplowing, each of which led to heavy losses of topsoil. The first occurred in the early 1930s when a severe multiyear drought led to extensive wind erosion in the southern Great Plains. The resulting environmental devastation not only gave the era its name, the Dust Bowl, but it triggered one of the largest internal migrations in U.S. history as droves of people left the southern Great Plains and headed west for California.51
After new agricultural practices were adopted in response to the Dust Bowl, such as planting windbreaks and strip-cropping land, with alternate-year fallowing, the soil was stabilized. But as demand for food began to climb rapidly after mid-century, and as grain prices reached record highs during the 1970s, farmers again began plowing from "fencerow to fencerow"—planting everything in sight. By 1982, the United States was losing annually an estimated total of 3.08 billion tons of topsoil from its cropland.52
In contrast to the Dust Bowl, when wind erosion in the Great Plains was the problem, this time it was mostly water erosion in the Corn Belt. In states such as Iowa, with its rolling farmland, farmers were losing almost 20 tons of topsoil per hectare each year from water erosion. A dozen U.S. studies analyzing the effect of erosion on land productivity found that losing an inch of topsoil reduced corn and wheat yields an average of 6 percent. With nature needing centuries to form an inch of topsoil, current losses are irreversible if time horizons are measured on a human time-scale.53
One consequence of overplowing is that countries eventually have to pull back and reduce the harvested area. Some have done this through carefully designed programs to convert highly erodible cropland back into grassland or forests. For example, the U.S. Conservation Reserve Program (CRP) launched in 1985 was designed to simultaneously control surplus production and conserve soil by retiring the most erodible land. Initiated and supported by environmental groups, the program encouraged farmers to take their highly erodible land out of production by providing government payments under 10-year contracts to plant the land in grass or trees.54
Within five years, U.S. farmers had converted nearly 15 million hectares of cropland, roughly 10 percent of the national total, to grassland. This reduced excessive soil erosion nationwide by some 40 percent, helping to enhance food security for the entire world. The nonmarket benefits from soil erosion reduction and the provision of habitat by the CRP between 1985 and 2000 are estimated to exceed $1.4 billion.55
The Soviet Union overexpanded its plowing with the Virgin Lands Project between 1954 and 1960. In an effort to boost farm output and become an agricultural superpower, the Soviets plowed up vast areas of grassland in Central Asia, an effort centered in Kazakhstan. During this period, the increase in wheat area in Kazakhstan was equal to the entire wheat area of Canada and Australia combined.56
Unfortunately, not all of this land could sustain cultivation. Much of the wheatland of Kazakhstan, a semiarid country, has eroded to the point where it can no longer support cropping. After the grain area reached 25 million hectares by 1960, it held there until 1984 or so, when it started shrinking as productivity fell and the less productive land was abandoned. By 2001, it had dropped to 12 million hectares. (See Figure 3-2.) Although this loss may have surprised the political leaders in Moscow who engineered the expansion in the 1950s, it did not surprise the soil scientists at the Institute of Soil Management in Alma Alta, who pointed out in 1994 that grain cultivation could be sustained on only half the area originally plowed. Even those estimates may prove to be overly optimistic.57
Whether topsoil loss, declining yields, and the abandonment of cropland in Kazakhstan can be arrested remains to be seen. Even the grainland still being farmed yields less than 1 ton of wheat per hectare—a fraction of the 7 tons per hectare in France, the leading wheat producer in Western Europe.58
If soil erosion proceeds too far, it can convert land to desert, becoming wasteland. At an intermediate stage of degradation, it can be returned to grassland, as in Kazakhstan, retaining some productive value. If the intervention comes early enough in the decline cycle, the land can be saved by managing it responsibly, as was the case during the Dust Bowl period. Or the land can be systematically retired and converted to grassland or woodland. Yet for many developing countries, where populations have doubled or even tripled over the last half-century, this is not always an option.
In the majority of developing countries, the growing demand for food has forced agriculture onto marginal lands. In China, for instance, a doubling of population since 1950 combined with record rises in income since 1980 have nearly tripled the demand for grain.59
China's loss of cropland to the construction of factories, roads, and expanding cities, particularly in the prosperous coastal provinces, led to mounting concern in Beijing about the country's shrinking cropland area. The result was an attempt to offset these losses by plowing more land in the semiarid northwest. But the newly plowed land, much less productive, was highly vulnerable to wind erosion.60
As described at the beginning of this chapter, in recent years dust storms in China have become more frequent and more intense, often covering cities in the northeast with layers of dust. In May 2000, the China Daily reported, "Disastrous sand storms that hit several major cities recently in North China have alarmed the nation about the devastating consequences of the development strategy that turned a blind eye on the environment." The desertification now under way in northwest China aroused public concern as "dust-laden blasts began to bury villages, blow into cities, and suffocate residents."61
These new reports, coupled with scientific studies, indicate that a dust bowl is forming in northern China. The April 2001 dust storm mentioned earlier was one of the largest ever recorded. U.S. scientists in Colorado measured the dust in this storm above them in Boulder at altitudes up to 10,700 meters (35,000 feet). China is losing millions of tons of topsoil, a depletion of its natural capital that it can ill afford.62
In Africa, population growth and the degradation of cropland are also on a collision course. Rattan Lal, an internationally noted agronomist at Ohio State University's School of Natural Resources, has made the first estimate of yield losses due to soil erosion for the continent. Lal concluded that soil erosion and other forms of land degradation have reduced Africa's grain harvest by 8 million tons, or roughly 8 percent. Further, he expects the loss to climb to 16 million tons by 2020 if soil erosion continues unabated.63
Among the countries experiencing unusually heavy soil losses are Nigeria, Rwanda, and Zimbabwe. Nigeria, Africa's most populous nation, is suffering from extreme gully erosion. Lal reports gullies 5-10 meters deep and 10-100 meters wide. In January 2001, Alhaji Sanni Daura, Nigeria's Minister of Environment, announced that the country was losing some 500 square kilometers of cropland to desertification each year. Daura is concerned that unless this desert encroachment can be reversed, Nigeria may soon face severe food shortages.64
On the northern edge of the Sahara, Algeria is also faced with the desertification of cropland. In December 2000, the agriculture ministry announced a four-year plan to halt the advancing desertification that they fear will soon threaten the fertile northern areas of the country. The plan is to convert the southernmost 20 percent of its grainland into tree crops, including fruit and olive orchards and vineyards. The government hopes that this barrier of permanent vegetation will halt the northward march of the Sahara. Out of desperation, Algeria, a country already dependent on imports for 40 percent of its grain, is willing to convert one fifth of its grain-producing land to tree crops in an attempt to protect the remaining four fifths.65
In East Africa, governments are facing a similar situation. Countries such as Ethiopia, Kenya, and Somalia are experiencing land degradation and cropland abandonment. Kenya's 1950 population of 6 million has increased to 31 million, putting unsustainable pressure on local forests, rangelands, and croplands. During the severe drought of 2000, the Masai, in an act of desperation, drove their cattle into Nairobi to feed on the grass in well-watered parks and residential lawns.66 The failure of Africa's governments to address the soil erosion threat effectively is depleting Africa's most essential natural capital—its soil. The next generation of farmers in Africa must try to feed not the 800 million people of today, but the projected 2 billion in the year 2025—and with far less topsoil.67
In Mexico, many of the 900,000 migrants who leave rural communities in arid and semiarid regions of the country each year are doing so because of desertification. Some of these environmental refugees end up in Mexican cities, others cross the northern border into the United States. U.S. analysts estimate that Mexico is forced to abandon 1,036 square kilometers (400 square miles) of farmland to desertification each year.68
The World Bank, citing studies for Costa Rica, Malawi, Mali, and Mexico, concludes that the gradual losses of agricultural productivity from soil erosion now translate into annual losses in farm output equal to 0.5-1.5 percent of these countries' gross domestic products. The toll of soil erosion on the earth's productivity can be seen in the abandoned villages in Ethiopia, where there is not enough soil left to support even subsistence-level agriculture. And in the former Soviet Union, land degradation, mostly from erosion, helped convert some 20 percent of the land in grain in 1977 either to soil-conserving forage crops, to alternate-year fallowing, or, where there was no effort to save the soil, to forest or wasteland by 1993.69
Unfortunately, many countries have not taken the initiative to reduce soil erosion and are paying a high price. For example, lost productivity on Africa's rain-fed cropland, virtually all from soil erosion, has reduced the annual harvest by an estimated $1.9 billion.70
The challenge is to arrest the excessive loss of topsoil on all land everywhere, reducing it to or below the level of new soil formation. The world cannot afford this loss of natural capital. If we cannot preserve the foundation of civilization, we cannot preserve civilization itself.
50. Wali et al., op. cit. note 5; WRI, op. cit. note 5.
51. Robert Henson, Steve Horstmeyer, and Eric Pinder, "The 20th Century's Top Ten U.S. Weather and Climate Events," Weatherwise, November/December 1999, pp. 14-19.
52. Grain prices from IMF, International Financial Statistics (Washington, DC: various years); topsoil loss from USDA, Economic Research Service, Agri-Environmental Policy at the Crossroads: Guideposts on a Changing Landscape, Agricultural Economic Report No. 794 (Washington, DC: January 2001), p. 16.
53. Loss of topsoil from water erosion from USDA, Summary Report: 1997 Natural Resources Inventory (Washington, DC: December 1999, rev. December 2000), pp. 46-51; effect of topsoil loss on yields in Leon Lyles, "Possible Effects of Wind Erosion on Soil Productivity," Journal of Soil and Water Conservation, November/December 1975, discussed in Lester R. Brown, "Conserving Soils," in Lester R. Brown et al., State of the World 1984 (New York: W.W. Norton & Company, 1984), pp. 62-65.
54. USDA, op. cit. note 52.
56. FAO, The State of Food and Agriculture 1995 (Rome: 1995), pp. 174-95; USDA, op. cit. note 5.
57. Figure 3-2 and Institute of Soil Management from FAO, op. cit. note 56; USDA, op. cit. note 5.
58. USDA, op. cit. note 5.
59. United Nations, op. cit. note 6; IMF, op. cit. note 49; USDA, op. cit. note 5.
60. Hong Yang and Xiubin Li, "Cultivated Land and Food Supply in China," Land Use Policy, vol. 17, no. 2 (2000).
61. "Combating Desertification," China Daily, 25 May 2000.
62. NCAR, op. cit. note 2; "Drought Promotes Sandstorms in North China," People's Daily, 10 March 2001; "Sandstorms to Increase in China," Xinhua, 10 April 2000; Gareth Cook, "Massive Dust Cloud to Travel Over N.E.," Boston Globe, 20 April 2001; Philip P. Pan, "In Inner Mongolia, Nature Lets Loose a Blizzard of Calamity," Washington Post, 21 January 2001; Dong Zhibao, Wang Xunming, and Liu Lianyou, "Wind Erosion in Arid and Semiarid China: An Overview," Journal of Soil and Water Conservation, vol. 55, no. 4 (2000).
63. Rattan Lal, "Erosion-Crop Productivity Relationships for Soils of Africa," Soil Science Society of America Journal, May-June 1995.
64. Ibid.; Samuel Ajetunmobi, "Alarm Over Rate of Desertification," This Day (Lagos, Nigeria), 23 January 2001.
65. "Algeria to Convert Large Cereal Land to Tree-Planting," Reuters, 8 December 2000.
66. United Nations, op. cit. note 6; Mark Turner, "You Can't Blame it All on the Weather," Financial Times, 14 October 2000.
67. United Nations, op. cit. note 6.
68. Michelle Leighton Schwartz and Jessica Notini, Desertification and Migration: Mexico and the United States, U.S. Commission on Immigration Reform Research Paper (San Francisco: fall 1994).
69. World Bank, World Development Report 1992 (New York: Oxford University Press, 1992), p. 56; soil erosion in Ethiopia from personal observation; grain area in the former Soviet Union from USDA, op. cit. note 5.
70. M. Kassas, "Desertification: A General Review," Journal of Arid Environments, vol. 30 (1995), p. 118.
Copyright © 2001 Earth Policy Institute