Terracing

Modern practices

Worldwide methods

The word terrace is applied to geological formations, architecture such as a housing complex built on a slope, or an island between two paved roads. However, the act of terracing specifies an agricultural method of cultivating on steeply graded land. This form of conservation tillage breaks a hill into a series of steplike benches. These individual flat structures prevent rain-water from taking arable topsoil downhill with it. The spacing of terraces is figured mathematically by comparing the gradient of the land, the average rainfall, and the amount of topsoil which must be preserved.

Different forms of terracing are required, depending upon how steep the ground is that is intended for cultivation. The bench is the oldest type, used on very steep territory. A little dam called a riser marks off each bench, and can slow down rainwater runoff on slopes as extreme as 30%. Just the way a steplike or “switchback” layout of railroad tracks prevent trains from having to go up one steep grade, the effect of gravity is lessened by bench terracing. Climate as well as soil condition and farming methods must be taken

into account, so the Zingg conservation bench is a type of flat-channel terrace constructed in semiarid climates. Slopes between each bench store runoff water after each rain.

Newer formats were developed to accommodate for mechanized farm equipment, so now variations such as the narrow-base ridge terrace and the broad-base terrace are used for less extreme gradients. Two approaches to broadbase terracing are used, depending upon the conditions of the topsoil and its vulnerability. The Nichols or channel variation is a graded broadbase terrace for which the soil is cultivated from above. Water is channeled off by this construction at a steady rate. The Mangum or ridge type is a level broadbase terrace used in permeable soil. This type shores up the topsoil from above and below. A less ambitious form than the broadbase is the steep-backslope terrace, which takes soil from the downhill side of a ridge, but this backslope cannot be used as cropland.

Modern practices

Parallel terraces are a recent innovation in conservation farming. This method incorporates land forming or landscaping by moving earth to make the terraces more uniform. The resulting formation allows room for the use of heavy machinery, and prevents “point rows,” which are areas that cannot be efficiently cultivated without doubling back over the same area. Modern terrace planning incorporates the use of topological maps, known more simply as contour maps, which take into account the surface variations of an area slated for cultivation. Otherwise, there is no need for special equipment for terracing, which can be done with an old-fashioned moldboard plow or with mechanized rigs like the bulldozer.

Worldwide methods

In Africa a certain method called “fanya juu” comes from the Swahili phrase meaning “make it up.” It began in Kenya during the 1950s, when standard Western practices could not control the fierce erosion in the area and also took too much arable land out of circulation. Fanya juu produces embankments by carving out ditches and depositing the soil uphill to form embankments. The ditches can be used to grow banana plants while another crop is planted on the embankments. A variation involving Western channel terracing is called “fanya chini,” but this is less popular because the ditches must be desilted of churned-up topsoil on a regular basis. Additionally, in very steep areas only bench terracing can be truly effective.

KEY TERMS

Agroecosystem —A agricultural ecosystem, comprised of crop species, noncrop plants and animals, and their environment.

Arable —An agricultural term describing fertile ground or topsoil, which can be cultivated as cropland.

Contour farming —The modern term for horizontal plowing or contour plowing, often used in conjunction with terracing to further prevent erosion.

Erosion —Damage caused to topsoil by rainwater runoff. There are various special terms for patterns of erosion caused in the soil, like sheet, rill, or gully erosion.

Point rows —These crop areas are “dead ends” in a field, which cannot be cultivated with modern heavy farm equipment without requiring the machines to turn and pass over them a second time, in order to reach the rest of the crops. These areas are prevented during terracing by moving arable turf to a more easily farmed area and smoothing.

Topographic map —A map illustrating the elevation or depth of the land surface using lines of equal elevation; also known as a contour map.

Yemeni mountain land was once cultivated widely by farmers, but it made for a difficult living. So when oil became a bigger economy than agriculture in the surrounding countries, the farmers slowly migrated to places like Saudi Arabia in order to seek greater fortunes in a new business. The agroecosystem left behind began to slowly contribute to soil erosion, because the arrangement of bench terraces, small dams and irrigation or runoff conduits was decaying. By 1987, one researcher found that thin or shoestring rills were deepening into gullies on the mountainsides.

The benches of Lebanon, some of which have existed for over two and a half thousand years after being instituted by the Phoenicians, were threatened by the battles of civil conflict in the area. Farmers were driven away to safer and more convenient living conditions in cities or in other countries. An investigation in 1994 warned of long-term damage to untended terraced lands including an increased possibility of landslides, and the chance that the land may be rendered eventually unfarmable.

Jennifer Kramer

Terracing

The word terrace is applied to geological formations, architecture such as a housing complex built on a slope, or an island between two paved roads. However, the act of terracing specifies an agricultural method of cultivating on steeply graded land. This form of conservation tillage breaks a hill into a series of steplike benches. These individual flat structures prevent rainwater from taking arable topsoil downhill with it. The spacing of terraces is figured mathematically by comparing the gradient of the land, the average rainfall, and the amount of topsoil which must be preserved.

Different forms of terracing are required, depending upon how steep the ground is that is intended for cultivation. The bench is the oldest type, used on very steep territory. A little dam called a riser marks off each bench, and can slow down rainwater runoff on slopes as extreme as 30%. Just the way a steplike or "switchback" layout of railroad tracks prevent trains from having to go up one steep grade, the effect of gravity is lessened by bench terracing. Climate as well as soil condition and farming methods must be taken into account, so the Zingg conservation bench is a type of flat-channel terrace constructed in semiarid climates. Slopes between each bench store runoff water after each rain.

Newer formats were developed to accommodate for mechanized farm equipment, so now variations such as the narrow-base ridge terrace and the broadbase terrace are used for less extreme gradients. Two approaches to broadbase terracing are used, depending upon the conditions of the topsoil and its vulnerability. The Nichols or channel variation is a graded broadbase terrace for which the soil is cultivated from above. Water is channeled off by this construction at a steady rate . The Mangum or ridge type is a level broadbase terrace used in permeable soil. This type shores up the topsoil from above and below. A less ambitious form than the broadbase is the steep-backslope terrace, which takes soil from the downhill side of a ridge, but this backslope cannot be used as cropland.

Modern practices

Parallel terraces are a recent innovation in conservation farming. This method incorporates land forming or landscaping by moving earth to make the terraces more uniform. The resulting formation allows room for the use of heavy machinery, and prevents "point rows," which are areas that cannot be efficiently cultivated without doubling back over the same area. Modern terrace planning incorporates the use of topological maps, known more simply as contour maps, which take into account the surface variations of an area slated for cultivation. Otherwise, there is no need for special equipment for terracing, which can be done with an old-fashioned moldboard plow or with mechanized rigs like the bulldozer.

Worldwide methods

In Africa a certain method called "fanya juu" comes from the Swahili phrase meaning "make it up." It began in Kenya during the 1950s, when standard Western practices could not control the fierce erosion in the area and also took too much arable land out of circulation. Fanya juu produces embankments by carving out ditches and depositing the soil uphill to form embankments. The ditches can be used to grow banana plants while another crop is planted on the embankments. A variation involving Western channel terracing is called "fanya chini," but this is less popular because the ditches must be desilted of churned-up topsoil on a regular basis. Additionally, in very steep areas only bench terracing can be truly effective.

Yemeni mountain land was once cultivated widely by farmers, but it made for a difficult living. So when oil became a bigger economy than agriculture in the surrounding countries, the farmers slowly migrated to places like Saudi Arabia in order to seek greater fortunes in a new business. The agroecosystem left behind began to slowly contribute to soil erosion, because the arrangement of bench terraces, small dams and irrigation or runoff conduits was decaying. By 1987, one researcher found that thin or shoestring rills were deepening into gullies on the mountainsides.

The benches of Lebanon, some of which have existed for over two and a half thousand years after being instituted by the Phoenicians, were threatened by the battles of civil conflict in the area. Farmers were driven away to safer and more convenient living conditions in cities or in other countries. An investigation in 1994 warned of long-term damage to untended terraced lands including an increased possibility of landslides, and the chance that the land may be rendered eventually unfarmable.

Resources

books

Moldenhauer, et al., eds. Development of Conservation Farming on Hillslopes. The Soil and Water Conservation Society, 1991.

Turner, B.L. Once Beneath the Forest. Boulder, CO: Westview Press, 1983.

periodicals

"Bench Terracing in the Kerinci Uplands of Sumatra." Journal of Soil & Water Conservation (September/October 1990).

"Rehabilitating the Ancient Terraced Lands of Lebanon." Journal of Soil & Water Conservation (March/April 1994).

"Terrace Channel Design and Evaluation." Transactions of theASAE (September/October 1992).

Jennifer Kramer

KEY TERMS

Agroecosystem

—A agricultural ecosystem, comprised of crop species, noncrop plants and animals, and their environment.

Arable

—An agricultural term describing fertile ground or topsoil, which can be cultivated as cropland.

Contour farming

—The modern term for horizontal plowing or contour plowing, often used in conjunction with terracing to further prevent erosion.

Erosion

—Damage caused to topsoil by rainwater runoff. There are various special terms for patterns of erosion caused in the soil, like sheet, rill, or gully erosion.

Point rows

—These crop areas are "dead ends" in a field, which cannot be cultivated with modern heavy farm equipment without requiring the machines to turn and pass over them a second time, in order to reach the rest of the crops. These areas are prevented during terracing by moving arable turf to a more easily farmed area and smoothing.

Topographic map

—A map illustrating the elevation or depth of the land surface using lines of equal elevation; also known as a contour map.

Terracing

A procedure to reduce the speed at which water is removed from the land. Water is directed to follow the gentler slopes of the terrace rather than the steeper natural slopes. Terracing is usually recommended only for intensively used, eroding cropland in areas of high-intensity rainfall. Terraces are costly to construct and require annual maintenance, but are feasible where arable land is in short supply or where valuable crops can be grown. In order to become self-sufficient in food production, ancient civilizations in Peru often constructed terraces in very steep, mountainous areas. Today, in Nepal, people living in the foothills of the Himalayas use terraces in order to have enough land available for food production.