14-3 Soil Erosion and Degradation

What Causes Soil Erosion? The Big Three

Land degradation occurs when natural or human-induced processes decrease the future ability of land to support crops, livestock, or wild species. One type of land degradation is soil erosion: the movement of soil components, especially surface litter and topsoil, from one place to another.

The two main agents of erosion are flowing water and wind, with water causing most soil erosion.

oil erosion has two major harmful effects. One is loss of soil fertility through depletion of plant nutrients in topsoil. The other harmful effect occurs when eroded soil ends up as sediment in nearby surface waters, where it can pollute water, kill fish and shellfish, and clog irrigation ditches, boat channels, reservoirs, and lakes.

How Serious Is Global Soil Erosion? Mostly Bad News

According to a study by the Consultative Group on International Agricultural Research, soil erosion and degradation has reduced food production on about 17% of the world’s croplands.

Some analysts contend that erosion estimates are overstated because they underestimate the abilities of some local farmers to restore degraded land. The UN Food and Agriculture Organization (FAO) also points out that much of the eroded topsoil does not go far and is deposited farther down a slope, valley, or plain. In some places, the loss in crop yields in one area could be offset by increased yields elsewhere.

Case Study: Soil Erosion in Canada

Wherever soil is left exposed, it can be eroded by wind and water. This natural process can be accelerated by human activities such as forestry, construction, agriculture, and land management.

Cultivated land that receives heavy precipitation is most likely to be affected by water erosion. In addition to the obvious loss to agriculture it causes, the displaced soil resulting from water erosion transports pesticides and fertilizers, fills canals and dams, and destroys fish habitat. By compromising water quality, it increases the cost of water treatment.

Case Study: Environmental Lessons Learned from the Dust Bowl

The agricultural activities of the settlers set the stage for severe wind erosion and crop failures. Before settlers began planting crops in the prairies, the deep and tangled root systems of native prairie grasses anchored the fertile topsoil firmly in place. But plowing the prairie tore up these roots, and the agricultural crops the settlers planted annually in their place had less extensive root systems. After each harvest, the land was plowed and left bare for several months, exposing it to high winds.

In the aftermath of the dust bowl experience, drought-alleviation programs were established in Canada and the United States. Measures to prevent further soil erosion included converting marginal farmland into pasture and planting hedgerows to serve as barriers against the wind.

What Is Desertification, and How Serious Is It? Decreasing Land Productivity

In desertification, the productive potential of arid or semi-arid land falls by 10% or more because of a combination of natural climate change that causes prolonged drought and human activities that reduce or degrade topsoil. The process can be moderate (a 10–25% drop in productivity), severe (a 25–50% drop), or very severe (a drop of 50% or more, usually creating huge gullies and sand dunes).

How Do Excess Salts and Water Degrade Soils? Crop Losses from Too Much Salt and Water

The one-fifth of the world’s cropland that is irrigated produces almost 40% of the world’s food. But irrigation has a downside. Most irrigation water is a dilute solution of various salts, picked up as the water flows over or through soil and rocks. Irrigation water not absorbed into the soil evaporates, leaving behind a thin crust of dissolved salts (such as sodium chloride) in the topsoil.

Repeated annual applications of irrigation water lead to the gradual accumulation of salts in the upper soil layers. This accumulation of salts is called salinization. It stunts crop growth, lowers crop yields, and eventually kills plants and ruins the land.