Earth Policy Institute on October 6, 2010
By Lester R. Brown
The literature on soil erosion contains countless references to the “loss of protective vegetation.” Over the last half-century, clearcutting, overgrazing, and overplowing have removed so much of that protective cover that the world is quickly losing soil accumulated over long stretches of geological time (see “Civilization’s Foundation Eroding”). Preserving the biological productivity of highly erodible cropland depends on planting it in grass or trees before it becomes wasteland.
Soil Conservation: The American Experience
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 with permanent vegetative cover under 10-year contracts. Under this program, farmers were paid to plant fragile cropland to grass or trees. The retirement of those 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 between 1982 and 1997. The U.S. approach offers a model for the rest of the world.
Another tool in the soil conservation toolkit—and a relatively new one—is conservation tillage, which includes both no-till and minimum tillage. Instead of the traditional cultural practices of plowing land and discing or harrowing it to prepare the seedbed, and then using a mechanical cultivator to control weeds in row crops, 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 addition to reducing erosion, this practice retains water, raises soil carbon content, and greatly reduces energy use for tillage.
In the United States, where farmers during the 1990s were required to implement a soil conservation plan on erodible cropland in order to be eligible for commodity price supports, the no-till area went from 7 million hectares in 1990 to 27 million hectares (67 million acres) in 2007. Now widely used in the production of corn and soybeans, no-till has spread rapidly in the western hemisphere, covering 26 million hectares in Brazil, 20 million hectares in Argentina, and 13 million in Canada. Australia, with 12 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.
Farming practices that reduce soil erosion and raise cropland productivity usually also lead to higher carbon content in the soil. Among these are the shift to minimum-till and no-till farming, the more extensive use of cover crops, the return of livestock and poultry manure to the land, expansion of irrigated area, a return to more mixed crop-livestock farming, and the forestation of marginal land.