The process of raising the world’s food has not always been kind to the environment. Many of the adverse environmental impacts resulting from agriculture are connected either to the loss of natural habitat that occurs when land is converted to agricultural purposes or to the use (or misuse) of pesticides and fertilizers. Yet soil degradation has also been a factor, and one with implications for food production as well.
By 1990, poor agricultural practices had contributed to the degradation of 562 million hectares, about 38 percent of the roughly 1.5 billion hectares in cropland worldwide . (See Degraded Soil Means Less Food.) Some of this land was only slightly degraded, but an appreciable amount was damaged severely enough to impair its productive capacity or to take it out of production completely. Since 1990, losses have continued to mount year by year, with an additional 5 million to 6 million hectares lost to severe soil degradation annually .
|Degraded Soil Means Less Food|
|Human-Induced Soil Degradation by Region and by Cause, 1945 to Late 1980s|
Source: World Resources Institute in collaboration with the United Nations Environment Programme and the United Nations Development Programme, World Resources 1992-93 (Oxford University Press, New York, 1992), Table 19.4, p. 290.
Degradation comes in several forms, the best known of which is soil erosion. Most soil erosion – about two thirds – is caused by water washing away topsoil, with another third caused by wind . One analysis of global soil erosion estimates that, depending on the region, topsoil is currently being lost 16 to 300 times faster than it can be replaced . Soil-making processes are notoriously slow, requiring from 200 to 1,000 years to form 2.5 centimeters of topsoil under normal agricultural conditions .
Farmland can be degraded in several other ways besides erosion. Physical degradation from mechanical tilling can lead to soil compaction and crusting. Repeated cropping without sufficient fallow periods or replacement of nutrients with cover crops, manure, or fertilizer can deplete soil nutrients. In addition, overapplication of agricultural chemicals can kill beneficial soil organisms .
Poor water management on irrigated cropland is a leading cause of degraded farmland. Inadequate drainage can lead to waterlogging of the soil or to salinization, in which salt levels build up in the soil to toxic levels. With some 10 to 15 percent of all irrigated land suffering some degree of waterlogging and salinization, these two problems alone represent a significant threat to the world’s productive capacity . (See Food Supply Increasingly Relies on Irrigation.)
Often, when climate and human activities combine to turn once-healthy soil into wasteland, the degradation is seemingly irreversible. However, many forms of degradation can be remedied through painstaking reconstruction of the soil’s health .
How much has damage to the world’s arable lands affected global food supply? Because total global food production has continued to increase over the years even in the face of significant soil degradation, it is tempting to view soil decline as a minor matter. However, factors such as increased fertilizer use, extension of irrigated lands, and higher cropping densities have masked the effects of soil degradation so far. Substantial yield losses have already occurred in certain regions, though few studies have attempted to quantify these losses. One 1994 study estimated that soil degradation between 1945 and 1990 lowered world food production some 17 percent . Regional studies have localized these losses. In Africa, production losses from soil erosion alone are estimated at just over 8 percent . Data from several different studies indicate that the decline in productivity resulting from soil degradation may exceed 20 percent in a number of Asian and Middle Eastern countries .
References and notes
1. L.R. Oldeman, “The Global Extent of Soil Degradation,” in Soil Resilience and Sustainable Land Use (CAB International, Oxon, U.K., 1994), p. 115.
2. United Nations Environment Programme (UNEP), Global Environment Outlook (Oxford University Press, New York, 1997), p. 236.
3. World Resources Institute in collaboration with the United Nations Environment Programme and the United Nations Development Programme, World Resources 1992-93 (Oxford University Press, New York, 1992), p. 114.
4. C. Barrow, Land Degradation (Cambridge University Press, Cambridge, U.K., 1991), cited in Henry Kendall and David Pimentel, “Constraints on the Expansion of the Global Food Supply,” Ambio, Vol. 23, No. 3 (1994), p. 200.
5. Henry Kendall and David Pimentel, “Constraints on the Expansion of the Global Food Supply,” Ambio, Vol. 23, No.3 (1994), p. 200.
6. Op. cit. 3, p. 115.
7. Nikos Alexandratos, ed., World Agriculture: Towards 2010 (Food and Agriculture Organization of the United Nations and John Wiley and Sons, Chichester, U.K., 1995), p. 359.
8. Sara Scherr and Satya Yadav, Land Degradation in the Developing World: Implications for Food, Agriculture, and the Environment to 2020, a synthesis of recommendations from an international workshop; Food, Agriculture, and the Environment Discussion Paper No. 14 (International Food Policy Research Institute, Washington, D.C., 1996), p. 3.
9. Pierre Crosson, “Degradation of Resources as a Threat to Sustainable Agriculture,” paper presented at the first World Congress of Professionals in Agronomy, Santiago, Chile, September 5-8, 1994.
10. Rattan Lal, “Erosion-Crop Productivity Relationships for Soils of Africa,” Soil Science Society of America Journal, Vol. 59, No. 3 (1995), pp. 661-667.
11. Op. cit. 8, pp. 1-2.