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Chapter 5. Protecting Cropland: Conserving Topsoil
In contrast to the loss of cropland to nonfarm uses, which is often beyond the control of farmers, the losses of soil and eroded land from severe erosion are within their control. Reducing soil losses caused by wind and water erosion to below the rate of new soil formation will take an enormous worldwide effort. Based on the experience of leading food producers such as China and the United States, as well as numerous smaller countries, easily 5 percent of the world’s cropland is highly erodible and should be converted back to grass or trees before it becomes wasteland. The first step to halting the decline in inherent land fertility is to pull back from this fast-deteriorating margin. 33
The key to controlling wind erosion is to keep the land covered with vegetation as much as possible and to slow wind speeds at ground level. Ground-level wind speeds can be slowed by planting shrubs or trees on field borders and by leaving crop residues on the surface of the soil. For areas with strong winds and in need of electricity, such as northwestern China, wind turbines can simultaneously slow wind speeds and provide cheap electricity. This approach converts an agricultural liability—strong winds—into an economic asset.
One time-tested method for dealing with water erosion is terracing, as is so common in rice paddies throughout the mountainous regions of Asia. On less steeply sloping land, contour strip farming, as found in the U.S. Midwest, works well. 34
Another tool in the soil conservation toolkit—and a relatively new one—is conservation tillage, which includes both no-till and minimum tillage. Farmers are learning that less tillage may be better for their crops. Instead of the traditional cultural practices of plowing land, discing or harrowing it to prepare the seedbed, and then planting with a seeder and cultivating row crops with a mechanical cultivator two or three times to control weeds, farmers simply drill seeds directly through crop residues into undisturbed soil. Weeds are controlled with herbicides. The only soil disturbance is the creation of a narrow slit where the seeds are inserted just below the surface. 35
This practice, now widely used in the production of corn and soybeans in the United States, has spread rapidly in the western hemisphere over the last two decades. (See Table 5–3.) Data for crop year 2003/04 show the United States with nearly 24 million hectares of land under no-till. Brazil had nearly 22 million hectares, Argentina 16 million, and Canada 13 million. Australia’s 9 million hectares rounds out the five leading no-till countries. 36
In the United States, the combination of retiring highly erodible land under the landmark Conservation Reserve Program that began in 1985, and required farmers to develop conservation plans on cropland eroding excessively, has sharply reduced soil erosion. In addition to the no-till cropland, 19 million more hectares were minimum-tilled, for a total of 43 million hectares of conservation tillage. Conservation tillage was used on 37 percent of the corn crop, 57 percent of the soybean crop, and 30 percent of wheat and other small grains. 37
Once farmers master the practice of no-till, its use can spread rapidly, particularly if governments provide economic incentives or require farm soil conservation plans for farmers to be eligible for crop subsidies. In the United States, the no-till area went from 7 million hectares in 1990 to nearly 24 million hectares in 2003/04, more than tripling. Recent FAO reports describe the growth in no-till farming over the last few years in Europe, Africa, and Asia. In addition to reducing both wind and water erosion, and particularly the latter, this practice also helps retain water, raises soil carbon content, and reduces the energy needed for crop cultivation. 38
|Table 5-3. Cropland Under No-Till in Key Countries, 2003/04|
|Source: See endnote 36.|
33. U. S. experience in 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; loss of topsoil from water erosion from USDA, op. cit. note 9; China from Chen Xiwen, Deputy Director, Development Research Center of the State Council, and colleagues, discussion with author in Beijing, 16 May 2002.
34. R. Neil Sampson, Farmland or Wasteland (Emmaus, PA: Rodale Press, 1981), p. 242.
35. USDA, Natural Resources Conservation Service, CORE4 Conservation Practices Training Guide: The Common Sense Approach to Natural Resource Conservation (Washington, DC: August 1999); Rolf Derpsch, “Frontiers in Conservation Tillage and Advances in Conservation Practice,” in D. E. Stott, R. H. Mohtar, and G. C. Steinhardt, eds., Sustaining the Global Farm, selected papers from the 10th International Soil Conservation Organization Meeting, at Purdue University and USDA-ARS National Soil Erosion Research Laboratory, 24–29 May 1999 (Washington, DC: 2001), pp. 248–54.
36. Table 5–3 from Rolf Derpsch and J. R. Benites, “Agricultura Conservacionista no Mundo,” presented at the Brazilian Soil Science Conference, Santa Maria, Brazil, July 2004.
37. USDA, Farm Service Agency Online, “History of the CRP,” in The Conservation Reserve Program, at www.fsa.usda.gov/dafp/cepd/12crplogo/history.htm, viewed 16 September, 2004; Derpsch and Benites, op. cit. note 36; Conservation Technology Information Center (CTIC), Purdue University, “1990–2002 Conservation Tillage Trends,” from 2002 National Crop Residue Management Survey, at www.ctic.purdue.edu/Core4/CT/CTSurvey/NationalData.html, viewed 23 September 2004; CTIC, Purdue University, “Crop Residue Management,” National Crop Residue Management Survey Data, at www.ctic.purdue.edu/Core4/CT/CT.html, viewed 23 September 2004.
38. CTIC, “1990–2002 Conservation Tillage Trends,” op. cit. note 37; Derpsch, op. cit. note 35; FAO, “Intensifying Crop Production With Conservation Agriculture,” at www.fao.org/ waicent/faoinfo/agricult/ags/AGSE/agse_e/general/CONT1.htm, viewed 30 September 2004.
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