Since the early 1980s, many farmers have adopted a new approach called conservation till­age, in which residues from previous crops are left in the soil, partially covering it and helping to hold it in place. The several types of conservation tillage include reduced tillage and no-tillage. Re­duced tillage, in which the subsurface soil is tilled without disturbing the topsoil, greatly reduces the amount of soil erosion. No-tillage leaves even the subsurface soil undisturbed, because special ma­chines punch tiny holes in the soil for seeds.

Conservation tillage increases the organic material in the soil, which in turn improves water-holding capacity. Decomposing organic matter releases nutrients more gradually than when conven­tional tillage methods are employed. Although conservation tillage is an effective way of reducing soil erosion, it requires greater use of herbicides to control weeds. Research is needed to develop alter­native methods of weed control for use with conser­vation tillage.

Crop Rotation

Farmers who practice effective soil conservation measures often use a combination of conservation tillage and crop rotation, the planting of a series of different crops in the same field over a period of years. When the same crop is grown continuously, pests tend to accumulate to destructive level so crop relation lessens damaged by insects and disease.

Also, many scientific studies haw .shown that continuously "rowing the same crop over a period of years depletes the soil of certain essential nutrients faster and makes soils more prone to erosion. Crop rotation is therefore effective in maintaining soil fertility and in reducing erosion.

A typical crop rotation would be corn soybeans-oats-alfalfa. Soybeans and alfalfa, both members of the legume family, actually increase soil fertility through their association with bacteria that fix atmospheric nitrogen into the soil. Thus, soybeans and alfalfa help produce higher yields of the grain crops with which they alternate in crop

Contour Plowing, Strip Cropping, and Terracing

Hilly terrain must be cultivated with care because it is more prone than flat land to soil erosion. Con­tour plowing, strip cropping, and terracing help control erosion of farmland with variable topogra­phy.

In contour plowing, fields are plowed and planted in curves that conform to the natural con­tours of the land, rather than in straight rows. Fur­rows run around, rather than up and down, hills.

Strip cropping, a special type of contour plow­ing, produces alternating strips of different crops along natural contours. For example, alternating a row crop such as corn with a closely sown crop such as wheat reduces soil erosion. Even more effective control of soil erosion is achieved when strip crop­ping is done in conjunction with conservation till.

In mountainous terrain, terracing produces level areas and thereby reduces soil erosion. Nutrients and soil are retained on the hor­izontal platforms instead of being washed away. Soils are preserved in a somewhat similar manner at low lying areas that are liked to make rice paddies.

Soil Reclamation

It is possible to reclaim land that is badly damaged from erosion. The United States has largely re­versed the effects of the 19 30s Oust Bowl, far exam­ple, and China has reclaimed badly eroded land in Inner Mongolia (northern China). Soil reclama­tion involves two steps: (1) stabilizing the land to prevent further erosion and (2) restoring the soil to its former fertility. In order to stabilize the land, the bare ground is seeded with plants; they eventually grow to cover the soil, holding it in place. For ex­ample, after the Dust Bowl, land in Oklahoma and Texas was seeded with drought-resistant grasses. One of the best ways to reduce the effects of wind on soil erosion is by planting shelter/belts, rows of trees that lessen the impact of wind.

The plants that have been established to stabi­lize the land start to improve the quality of the soil almost immediately, as dead portions are converted to humus. The humus holds mineral nutrients in place and releases them a little at a time; it also improves the water-holding capacity of the soil.

Restoration of soil fertility to its original level is a slow process, however. During the soil's recov­ery, use of the land must he restricted: it cannot be farmed or grazed. Disaster is likely if the land is put back to use before the soil has completely recov­ered. But restriction of land use for a period of sev­eral to many years is sometimes very difficult to accomplish. How can a government tell landown­ers that they may not use their own land? How can land use be restricted when people's livelihoods and maybe even their lives depend upon it?

Soil Conservation Policies in the United States

The disastrous effects of the Dust Bowl years on U.S. soils focused attention on the fact that soil is a valuable natural resource. Upon passage of the Soil Conservation Act in 1935, the Soil Conservation Service was formed; its mission is to assess soil dam-aye and develop policies to improve and sustain our soil resource.

Historically, farmers have been more likely to practice soil conservation during hard financial limes and periods of agricultural surpluses, both of which translate into lower prices for agricultural products. When prices are high, with a good market for agricultural products, farmers have more incen­tive to put every parcel of land into production, including marginal, highly erodible lands. During

times when the farm economy has been strong, federal soil conservation programs have actually contributed to production on marginal lands by relying on voluntary rather than mandatory compliance. Ik¹ federal government has traditionally used in­centives, miner .than penalties for noncompliance, to encourage .soil conservation practices.

In a different approach, the Conservation Re­serve Program (CRP), which is part of the Food Security Act of 1985, pays farmers to stop producing crops on highly erodible farmland. It requires planting grasses or trees on such land and then "retiring it from further use for ten years. This land may not be grazed, nor may be harvested for hay during that period. The CRP required that as of 1990, all land designated as highly erodible he placed either in the CRP or in a locally approved soil conservation program. The provisions of the CRP must he fully implemented by 1995 or farmers will not be eligible for any fed­eral program benefits, such as diversion payments, Farmers Home Administration loans, federal crop insurance, and conservation reserve payments. When the CRP is fully implemented, soil erosion from the most vulnerable lands should be reduced considerably.

The U.S. government is also trying to reduce soil erosion in drought-prone areas of the West and Southwest by retiring marginal farmlands and al­lowing them to revert to their natural states. The U.S. Department of Agriculture (USDA) shares with farmers the cost of planting ground covers to stabilize this land.