Conserving and Rebuilding Soils
In reviewing the literature on soil erosion, references to the "loss of protective vegetation" occur again and again. Over the last half-century, we have removed so much of that protective cover by clearcutting, overgrazing, and overplowing that we are fast losing soil accumulated over long stretches of geological time. Eliminating these excesses and the resultant decline in the earth's biological productivity depends on a worldwide effort to restore the earth's vegetative cover, an effort that is now under way in some countries.
The 1930s Dust Bowl that threatened to turn the U.S. Great Plains into a vast desert was a traumatic experience that led to revolutionary changes in American agricultural practices, including the planting of tree shelterbelts -- rows of trees planted beside fields to slow wind and thus reduce wind erosion -- and strip-cropping, the planting of wheat on alternate strips with fallowed land each year. Strip-cropping permits soil moisture to accumulate on the fallowed strips, while the alternating planted strips reduce wind speed and hence erosion on the idled land.
In 1985, the U.S. Congress, with strong support from the environmental community, created the Conservation Reserve Program (CRP) to reduce soil erosion and control overproduction of basic commodities. By 1990 there were some 14 million hectares (35 million acres) of highly erodible land in permanent vegetative cover under 10-year contracts. Under this program, farmers were paid to plant fragile cropland to grass or trees. The retirement of 14 million hectares under the CRP, together with the use of conservation practices on 37 percent of all cropland, reduced U.S. soil erosion from 3.1 billion tons to 1.9 billion tons during the 15 years from 1982 to 1997. The U.S. approach to controlling soil erosion by both converting highly erodible cropland back to grassland or trees and adopting soil conservation practices offers a model for the rest of the world.
The conversion of cropland to nonfarm uses is often beyond the control of farmers, but the losses of soil and eroded land from severe erosion are not. Lowering soil losses caused by wind and water erosion below the gains in new soil formed by natural processes will take an enormous worldwide effort. Preserving the biological productivity of highly erodible cropland depends on planting it in grass or trees before it becomes wasteland. The first step in halting the decline in inherent land fertility is to pull back from this fast-deteriorating margin.
Terracing, a time-tested method for dealing with water erosion, is 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.
Another tool in the soil conservation toolkit -- and a relatively new one -- is conservation tillage, which includes both no-till and minimum tillage. In addition to reducing erosion, this practice helps retain water, raises soil carbon content, and reduces the energy needed for crop cultivation. Instead of plowing land, discing or harrowing it to prepare the seedbed, and then using a mechanical cultivator to control weeds, farmers simply drill seeds directly through crop residues into undisturbed soil, controlling weeds with herbicides. The only soil disturbance is the narrow slit in the soil surface where the seeds are inserted, leaving the remainder of the soil undisturbed, covered by crop residues and thus resistant to both water and wind erosion.
In the United States, where farmers during the 1990s were required to implement a soil conservation plan on erodible cropland to be eligible for commodity price supports, the no-till area went from 7 million hectares in 1990 to 25 million hectares in 2004. Now widely used in the production of corn and soybeans in the United States, no-till has spread rapidly in the western hemisphere, covering 24 million hectares in 2004 in Brazil, 18 million hectares in Argentina, and 13 million in Canada. Australia, with 9 million hectares, rounds out the five leading no-till countries.
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. Recent reports from the United Nations Food and Agriculture Organization describe the early growth in no-till farming over the last few years in Europe, Africa, and Asia.
Algeria, trying to halt the northward advance of the Sahara Desert, announced in December 2000 that it is concentrating its orchards and vineyards in the southern part of the country, hoping that these perennial plantings will halt the desertification of its cropland. In July 2005, the Moroccan government, responding to severe drought, announced that it was allocating $778 million to cancel farmers' debts and to convert cereal-planted areas into less vulnerable olive and fruit orchards.
There are similar concerns about the expanding Sahara on the southern edge of the desert as well. President Olusegun Obasanjo of Nigeria has proposed planting a Great Green Wall of trees, a band five kilometers wide stretching 7,000 kilometers across Africa, in an effort to halt the desert's advance. Senegal, which is on the western end of this proposed wall and is losing 50,000 hectares of productive land each year, strongly supports the idea. No one knows how long this project would take, but Senegalese environment minister Modou Fada Diagne observes, "Poverty and desertification create a vicious cycle.”¦ Instead of waiting for the desert to come to us, we need to attack it." China also is trying to halt the advance of deserts with its own Great Green Wall. In addition, it is paying farmers in the threatened provinces to plant their cropland in trees. The goal is to plant trees on 10 million hectares of grainland, easily one tenth of China's current grainland area.
In Inner Mongolia, efforts to halt the advancing desert and to reclaim the land for productive uses rely on planting desert shrubs to stabilize the sand dunes. And in many situations, sheep and goats have been banned entirely. In Helin County, south of the provincial capital of Hohhot, the planting of desert shrubs on abandoned cropland has now stabilized the soil on the county's first 7,000-hectare reclamation plot. Based on this success, the reclamation effort is being expanded.
The Helin County strategy centers on replacing the large number of sheep and goats with dairy cattle, increasing the number of dairy animals from 30,000 in 2002 to 150,000 by 2007. The cattle are kept in enclosed areas, feeding on cornstalks, wheat straw, and the harvest from a drought-tolerant forage crop resembling alfalfa, which is grown on reclaimed land. Local officials estimate that this program will double incomes within the county during this decade.
To relieve pressure on the country's rangelands, Beijing is asking herders to reduce their flocks of sheep and goats by 40 percent. But in communities where wealth is measured in livestock numbers and where most families are living in poverty, such cuts are not easy or, indeed, likely, unless alternative livelihoods are offered pastoralists along the lines proposed in Helin County.
The only viable way to eliminate overgrazing on the two fifths of the earth's land surface classified as rangelands is to reduce the size of flocks and herds. Not only do the excessive numbers of cattle, and particularly sheep and goats, remove the vegetation, but their hoofs pulverize the protective crust of soil that is formed by rainfall and that checks wind erosion. In some situations, the only viable option is to keep the animals in enclosures, bringing the forage to them. India, which has successfully adopted this practice for its thriving dairy industry, is the model for other countries. Protecting the earth's remaining vegetation also warrants a ban on the clearcutting of forests in favor of selective harvesting, simply because with each clearcut there are heavy soil losses until the forest regenerates. Thus with each subsequent cutting, productivity declines further. Restoring the earth's tree and grass cover protects soil from erosion, reduces flooding, and sequesters carbon. It is one way we can restore the earth so that it can support our children and grandchildren.
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This piece follows "Losing Soil," on-line at www.earthpolicy.org/Books/Seg/PB2ch05_ss3.htm.
Adapted from Chapter 8, "Restoring the Earth," in Lester R. Brown, Plan B 2.0: Rescuing a Planet Under Stress and a Civilization in Trouble (New York: W.W. Norton & Company, 2006), available on-line at www.earthpolicy.org/Books/PB2/index.htm
Additional information at www.earthpolicy.org
Source: Earth Policy Institute