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Erosion

Soil erosion is a gradual process that occurs when the actions of water, wind, and other factors eat away and wear down the land, causing the soil to deteriorate or disappear completely. The main agents of soil erosion are wind, water, and tillage. Maintaining a continuous vegetative cover on the soil is usually the best way to control erosion. Soil deterioration and low quality of water due to erosion and run off has often become a severe problem around the world. Many times the problems become so severe that the land can no longer be cultivated and is abandoned. The key to minimizing soil erosion and saving the farm lands is the farmer himself. Ultimately, he is the one who must reduce the level at which erosion sediments are dislodged from his cropland.

Studies in water quality relating to agriculture have shown that, of the four to five billion tons of sediment being deposited in the country's streams each year, over half is coming from croplands. The deposited soil, which contains pesticides, farm chemicals, and nutrients vital to the crops but damaging to ground water, gets there mainly as a result of runoff due to rainstorms and sheet erosion.

Runoff occurs when the rainfall rate exceeds the soil's infiltration capacity. On sloping areas, runoff is a concern since it can carry soil particles, nutrients, and other chemicals with it.

Geological erosion occurs where soil is in its natural environment surrounded by its natural vegetation. This has been taking place naturally for millions of years and has helped create balance in uncultivated soil that enables plant growth. A classical example of the results of geological erosion is the Grand Canyon.

Accelerated erosion can be caused by man's activities, such as agriculture and construction, which alter the natural state of the environment.


Wind Erosion

Wind erosion, or "soil drifting" is caused by the action of wind on exposed soil, especially smooth, unprotected surfaces. Wind picks up finer soil particles and deposits them downwind. Improper tillage practices, low soil moisture, poor soil cover or any combinations thereof can increase the risk of wind erosion.

Drip irrigation is a successful, economical way to water new windbreaks.

The second most common erosion control practice in Canada is the use of windbreaks or shelterbelts, which are lines of trees or bushes planted at the borders of or within fields, normally at right angles to the prevailing winds (maintaining natural vegetation along fencelines has the same effect). This technique is most commonly used in the Prairies (29 to 37 percent of farms), where the flat terrain, minimal natural brush protection, large fields, and frequency of high winds make cultivated land especially vulnerable to wind erosion. Ontario farms also report substantial use of windbreaks (21 percent of farms).


Water Erosion

Water erosion occurs when rain, spring run-off, or floodwater carry soil particles away. This can occur through sheet erosion, where soil materials are removed relatively uniformly, or rill erosion where flowing water creates small channels in the soil, called rills, and larger channels, called gullies. The extent of water erosion depends on the amount of soil cover, soil texture, the length and grade of the field slope, the amount and timing of heavy rainfall, and the tillage and cropping practices used. Raindrops can be a major problem for farmers when they strike bare soil. With an impact of up to 30 mph, rain washes out seed and splashes soil into the air. If the fields are on a slope the soil is splashed downhill which causes deterioration of soil structure. Soil that has been detached by raindrops is more easily moved than soil that has not been detached.

Sheet erosion is caused by raindrops. Sheet erosion is defined as the uniform removal of soil in thin layers from sloping land. This, of course, is nearly impossible; in reality the loose soil merely runs off with the rain.

Rill erosion is the most common form of erosion. Although its effects can be easily removed by tillage, it is the most often overlooked. It occurs when soil is removed by water from little streamlets that run through land with poor surface draining. Rills can often be found in between crop rows.

Gullies are larger than rills and cannot be fixed by tillage. Gully erosion is an advanced stage of rill erosion, just as rills are often the result of sheet erosion.


Tillage

Tillage erosion happens when the action of tilling drags soil downhill. The extent of tillage erosion depends on the shape and gradient of the slope, the type of equipment, depth of tillage, the speed at which tillage equipment is used, and the number of tillage operations.

Tillage and planting practices that reduce erosion include contour cultivation and strip-cropping. Contour cultivation is cultivation that follows the contours of a field, producing furrows that run perpendicular or at angles to the slope-line of a field. This creates an irregular surface that breaks up the downslope movement of water and thus reduces water erosion of the soil. This cultivation technique is practiced in Canada in the Prairies (11 to 18 percent of farms) and Prince Edward Island (10 percent of farms). Strip-cropping, a technique that involves alternating strips (50 to 200 metres wide) of crop and summerfallow or of two crops across a field, is less commonly used in Canada.

Tillage practices are used for wind erosion control by producing a rough, cloddy surface that maintains surface residue and conserves soil moisture. When used along with crop residues, also known as stubble mulch tillage, reduced tillage, or conservation tillage, it reduces wind velocity and traps eroding soil.

An implement used for emergency wind erosion control should gently lift the soil, creating as many and as large of clods as possible. Disks and harrow-type implements with several ranks of closely spaced tines generally will not be effective, and should not be used.

In fine or medium textured soils, most types of chisel, lister, or broad shovel points create a ridge and bring clods to the surface. The shank and/or point should produce a gentle lifting action to bring clods to the surface and to avoid breaking them. An angled, wide point which lifts the soil usually creates larger clods and a larger ridge than a point that has a straight, narrow, vertical shape.

Narrow points 2 to 4 inches wide require a shank spacing of about 24 inches for best results. Wider shovels or lister bottoms that create a larger ridge can be spaced 36 to 48 inches apart. Tillage depth to produce maximum roughness generally varies between 4 and 12 inches, depending on soil conditions.

Moist or heavy soils often provide good ridges and clods with tillage depths of 4 to 8 inches. Dry or sandy soils generally require deeper tillage.

Field speed for emergency tillage depends on the implement, soil conditions, and depth of tillage. In general, slow speeds produce more clods while faster speeds provide more ridging effect. Speeds of 3 to 4 mph usually result in the most effective surface. For best results, vary both implement depth and field speed to determine the combination producing maximum overall roughness.

It often is difficult to obtain effective clods and roughness in sandy soils, and the roughness is often short-lived. Wide shovels or lister bottoms spaced 40 to 50 inches apart usually provide the best combination of clods and ridges in sandy soil.

If more than one emergency tillage operation is anticipated, use a shallow depth (4 to 6 inches) the first time. Follow with a deeper tillage the second time, with new furrows spaced between the original furrows. Vary the face angle of the tillage tool, depth of operation, and field speed to obtain the best combination.

In sandy soils it usually is best to anticipate emergency tillage will be required, and time the operation to obtain the best roughness. Some operators obtain best results soon after a rainfall when the soil is moist and the implement shanks follow tractor tire tracks. Clods readily form in sandy soil when the soil surface is moist and has been lightly compacted.

Other operators prefer a soil ripper to bring up large, dry clods when subsurface soil is dry. Still others attempt to time the operation when the top two inches of soil is frozen, to bring up frozen clods. One danger is that the soil may freeze too fast or too deep before the operation is completed.

Emergency tillage can be used in a field planted to winter wheat. If wind erosion occurs, it is better to control the damage early using emergency tillage, rather than risk losing the entire crop. Use narrow chisel points spaced 4 to 6 feet apart, 4 to 6 inches deep. Tillage direction should be perpendicular or at an angle to the wheat row to minimize plant injury.

Data from a five year study at two sites in Kansas suggests this type of emergency tillage has minimal effect on potential yield, but can reduce the damage to growing wheat and can reduce soil loss in moderate erosion situations. This study found emergency tillage caused the most damage to wheat yields when the wheat had just emerged. The least yield reduction was found when the tillage was done in fields with wheat plants already tillered. Emergency tillage is not effective if clods cannot be brought to the surface, and is not possible after the soil has frozen more than 2 inches deep.

Row crops just planted or just emerged often are vulnerable to wind erosion, and can be protected by emergency tillage. Growers often equip their planters with narrow, flat running sweeps to pull clods to the surface during planting. This is especially important between crop rows where tractor or planter tires leave smooth surfaces with no clods.

After planting, rotary hoes, strippers (implements with several rotary hoe type wheels between each crop row) and cultivators are used to create clods on the soil surface. These operations are carried out both in anticipation of wind erosion, and after erosion begins. The most effective time is often after a rain. A heavy rain will melt any clods present and create a soil surface that blows easily.

Effective clods can be created at the soil surface if emergency tillage is done soon after the rain when there is considerable moisture in the top 2 inches of soil. Although emergency tillage can be effective in row crop situations after the soil begins to erode, tillage in moist soil conditions in anticipation of erosion almost always will be better.

Tillage is also very effective in controlling rill and sheet erosion. The rough surface along with crop residues prevents rain water from carrying of soil particles and other organic matter.


Management Practices

Erosion control methods include maintaining a cover on the soil, particularly at times of the year when soil is most vulnerable to erosion. Winter cover crops, such as fall rye and winter wheat, can be planted after fall harvest so that soil is not left exposed over the normally barren and highly erosive fall and spring months. Ontario farms report using winter cover crops at double the figure for all of Canada (20 percent versus 10 percent). Grassed waterways, which are grassy strips in run-off depressions that provide a route for excess water, are generally used more in western Canada and Ontario than in the east.

There are several accepted Best Management Practices (BMP) that are used frequently in controlling erosion factors of both wind and water. They range from better utilization of the natural environment to the construction of artificial devices, but all can be effective in minimizing potential damage. Some of these BMPs include the following:

Crop rotation improves the overall efficiency of nitrogen uptake and utilization in the soil. If certain cover crops are planted in the winter, erosion and runoff is prevented when the ground thaws, and nutrients are trapped in the soil and released to the spring crops. Growing forages in rotations is the most common erosion control practice in Canada; 42 percent of farms report this practice. In general, the semi-arid regions of the Prairies have little opportunity to use forages for erosion control due to inadequate soil moisture during the growing season; in contrast, the important practice of "stubble mulch cropping" is commonly employed in these areas for erosion control.

There are many reasons why crop rotation is an effective way to make farmlands more productive.

  1. The yield advantages of crops being rotated has been proven by data to be much higher than that of continuous crops.
  2. There is evidence that conservation tillage systems which leave much of the prior crop residues on the soil surface are much better adapted to crop rotations than to that of continuous crops.
  3. Rotating crops provides greater yield advantages when using some form of conservation tillage.
  4. Residues from sod crops, corn, and soybeans influence certain soil physical properties that, in turn, influence soil drainage and aeration.
  5. Rotating crops can reduce the potential for serious insect and disease infestations associated with specific residues. This is especially important if continuous corn or soybeans is produced under conservation tillage, since residues are left on the surface year 'round harbor insects and disease.

Contour Cultivation. On gently sloping land, contour cultivation, a special tillage practice carried out on the contour of the field, can reduce the velocity of overland flow. Contour cultivation should not be carried out on steep slopes though, because it will merely make the erosion situation worse.

Strip Cropping. Strip cropping is a technique in which alternate strips of different crops are planted in the same field. There are three main types of this BMP: contour strip cropping, field strip cropping, and buffer strip cropping. This BMP is used to control both wind and water erosion. If the strips are planted along the contour, water damage can be minimized; in dry regions, if the strips are planted crosswise to the contour, wind damage is also minimized.

Terraces

Grass Waterways. When trying to reduce the possibility of severe gully erosion, grassed waterways provide a helpful solution. They force storm runoff water to flow down the center of an established grass strip and can carry very large quantities of storm water across a field without erosion. Grass waterways are also used as filters to remove sediment, but may sometimes loose their effectiveness when too much sediment builds up in the waterways. To prevent this, it is important that crop residues, buffer strips, and other erosion control practices and structures be used along with grass waterways for maximum effectiveness.

Diversion Structures. Diversion structures are channels that are constructed across slopes that cause water to flow to a desired outlet. They are similar to grass waterways and are used most often for gully control.

Drop Structures. Drop structures are small dams used to stabilize steep waterways and other channels. They can handle large amounts of runoff water and are effective where falls are less than 2.5 meters. In channel stabilization, drop structures such as a straight drop spillway are constructed to direct the flow of water through a weir(some type of enclosure such as a fence or dam in a stream to raise the water level or to divert the flow), into a stilling basin where the energy of the water is dissipated before it flows into the channel below. The straight drop spillway may be used with drops only up to ten feet. Chutes and flumes are used much in the same manner for steeper grades.

Riparian Strips. Riparian strips are merely buffer strips of grass, shrubbery, plants, and other vegetation that grow on the banks of rivers and streams and areas with water conservation problems. The strips slow runoff and catch sediment. In shallow water flow, they can reduce sediment and the nutrients and herbicides attached to it by 30% to 50%.

Conservation Tillage. Regular conventional tillage provides a smooth, unridged soil surface that can encourage serious runoff and erosion problems on sloping crop land. Instead, conservation tillage is any tillage planting system that leaves at least 30% of the field surface covered with crop residue after planting is completed and involves reduced or minimum tillage.

There are several types of conservation tillage currently being used in the Midwest Corn Belt as effective BMPs. They include:

Artificial Devices. Such artificial devices include earthen dams, broken rock, rock barriers, slat/brush fences, board walls, log, timber, or brick barriers, and verticle burlap windbreakers provide protection against wind water erosion. Brush matting, gravel, rock or spray-on adhesive may be used on the surface itself for protection from erosion. There are many BMPS that may be utilized, depending on the situation, severity, and surroundings of each case.

Earthen Dams. The main reasons for building dams are:

  1. To trap sediment.
  2. To stabilize drainage ways and reduce erosion.
  3. To store excess water temporarily to reduce flood damage.
  4. To store water for livestock, irrigation, household, or municipal use.

There are several types of dams, which include soil-saving dams, grade-stabilization dams, and flood control dams.

Broken Rock. Stone and broken rock coverings are a simple and long used technique to reduce erosion in waterways and gullies. "Riprap," which is a loose covering of stone on the soil surface, has been widely employed for this purpose. It has also been used on the front slopes of earthen dams to prevent wave action from wearing the front of the dam. The stones have been sorted and placed by hand in the past, but are now usually merely dumped over the surface and smoothed over with a machine. More rock is required this way, but the amount of labor is reduced. Broken rock is a very expensive technique that is being used less and less except for in areas where rock is a widely available natural resource.

Rock Barriers. A barrier or series of barriers is often needed to reduce the erosive power of water in steeply sloping waterways and in many gullies so vegetation can be established. Erosion is reduced by the flatter slope between barriers, and vegetation has a chance to grow on the more level areas.

Slat/Brush Fences. To anchor brush barriers in place, two rows of posts are driven vertically into the soil across the waterway or gully bed. Loose branches or small trees are packed tightly in between the rows of posts, making an impermeable barrier. The ends of the brush piles should be dug into the channel walls and the soil should be packed tightly around them. The top of the brush pile normally is low in the middle so no water will flow around the ends.

Log Barriers. Logs may be used to form barriers in larger gullies. Sturdy posts are driven deeply into the channel sides and bottom as for brush barriers. The logs often must be dug into the bottom as well as the sides so they make firm contact with the soil.

Timber Barriers. Heavy dimension lumber or timber, or a series of thick posts driven closely together can also serve as a barrier. Posts should be driven vertically into the soil, deeper than the length of the exposed part above ground so the force of the water cannot overtop the barrier. Large thick pieces of termite-resistant wood help guarantee the long life of the structure.

Brick Barriers. Brick barriers can be used to stop gully erosion. A good foundation such as poured concrete or layered rock is necessary for any barrier built with bricks or blocks. This, along with supporting butresses, should resist the force of the water where the barrier meets the gully wall.


Soil Abrasion and Erosion Control

Dry soil conditions can present problems with wind erosion. Under windy conditions, dry, loose soil particles can become dislodged and airborne. This had been a serious problem in other parts of the country prior to implementing erosion control conservation practices, such as wind breaks and cover crops. Many microirrigated fields result in dry row middles and other non-cropped areas of the field. Similarly, fields between crop cycles may have bare, non-cropped soil conditions which become susceptible to drying and potential erosion.

Airborne soil particles, particularly sands, can also become abrasive to plants and fruit. These abrasions may provide an entrance on the surface of the plant tissue for plant pathogens or they may simply scar the surface of the fruit. Either situation can result in lower quality plants and fruit.

Drought tolerant cover crops may assist in preventing erosive conditions by taking advantage of natural rainfall. However, sometimes these crops may need initial irrigation water for germination or a periodic irrigation during periods of very low or infrequent rainfall.


Synthetic Polymer for Soil Erosion Control

Results from a USDA Agricultural Research Service study in Kimberly, Idaho indicated that polyacrylamide, a synthetic polymer, can reduce soil erosion under furrow-irrigated agriculture to nearly zero. The scientists found that just 10 parts per million (equal to about a pinch of salt in 10 gallons of water) of polyacrylamide added to irrigation water prevented water from
carrying soil particles away as it flowed down furrows. The treatment was effective even when added during the first hour of the 8-12 hour irrigation period.

More than 23 million acres of U.S. corn, beans, barley, and other crops are watered by furrows. While furrow irrigation per se is not practiced in Virginia, other forms of irrigation, e.g. travelling gun, employed in the production of furrowed crops, i.e. potatoes, tobacco, etc., possess as much or greater potential for soil erosion. Over two billion tons of soil wash off the world's irrigated croplands annually and a soil additive such as polyacrylamide may have application in other situations where erosion hazards exist.

In another study, straw mulching and polyacrylamide injection treatments for furrow erosion control were evaluated in an on-farm comparison under deficit irrigation for irrigation performance, erosion reduction and crop yield under two slope conditions. Both treatments greatly reduced erosion and significantly affected irrigation performance.


Geomembranes

This material is used to line ponds in areas where the soil continues to seep water. It is also used to cover and protect equipment and other items from the elements.


Intercropping System for Erosion Control

According to a recent study from India, trees and woody tree crops on your farm may control erosion on sloping sites, improve soil physical conditions, fertility, hydrological characteristics. When interplanted with food crops, yields may decline, but the long term benefit to the soil gained from such an intercropping system is considerable.

The experiment was carried out on sloping laterite soils of south India, and included plantings of: Eucalyptus tereticornis, Leucaena leucocephala, cassava, groundnut, and french beans/cowpea.

Each crop was grown in monoculture as well as in intercropped plots. Five types of intercropping treatments were performed: 1 tree crop + cassava; 2 tree crop + cassava + groundnut; 3 tree crop + cassava + cowpea; 4 tree crop + groundnut; 5 tree crop + cowpea. Each set of treatments were carried out once with Leucaena and again with Eucalyptus.

Effects on Yields. Yields of both cassava and the seasonal intercrops were reduced when grown in association with one of the tree crops. The pod yields of groundnut and cowpea were higher when intercropped with cassava and lower when grown in association with one of the tree crops + cassava. While intercropping with cassava reduced yields of Leucaena, it improved that of Eucalyptus. Forage yield of Leucaena was lowest (4.83 t/ha) when grown in association with cassava, and greatest (7.50 t/ha) when grown with cassava + groundnut.Eucalyptus benefited from association with cassava, as indicated by pre-harvest trunk girth. Cassava + groundnut intercropping resulted in the best growth of Eucalyptus, as judged by percent of trees with a girth greater than 30 cm. The maximum air dried wood yield (43.5 t/ha), however, was reached when the tree was grown with cassava + cowpea. Intercropping had a definite positive effect on Eucalyptus yield since monocropped plantings of Eucalyptus yielded only 30.1 t/ha of wood.

The benefit of intercropping tree crops with cassava is in the reduced run off and soil loss. The disadvantage of intercropping trees with cassava was that yields fell after the first year. Leucaena and Eucalyptus are very efficient in removing nutrients from the soil.

Effect on Soil Qualities. Initially the soil in all the plots was acidic, the organic carbon content was medium to high, and the nutrient availability was low to medium. The pH did not change after three years of cropping. The organic carbon content of the soil improved in plots of monocropped cassava and in plots of cassava intercropped with the tree crops, and showed a decline where tree crops were grown alone. Mono-cropping of Leucaena and Eucalyptus also reduced the available nutrients of the soil. During all three years the nutrient removal by cassava was greater when grown alone, as compared to the cassava-tree crop combinations. Of those combinations, cassava + Eucalyptus had the lowest nutrient removal rate.

Chemical assays of plant parts indicated that cassava utilized more soil nutrients when planted alone, and considerably less when grown with Eucalyptus. These results further demonstrate the aggressive habit of fast growing tree crops; they effectively utilize available nutrients and moisture at the expense of companion crops, and they considerably reduce soil fertility when grown continuously for three years, especially in monocultural plantation forests. If cassava were intercropped with the tree crops, however, the fertility status of the soil could be maintained without much deterioration.

Soil erosion was most effectively controlled in the two tier cropping of tree crop + cassava. Here the soil loss was 70%-80% less than mono crops of cassava, Eucalyptus, or Leucaena. Runoff and soil loss were effectively reduced when cassava was grown on staggered soil mounds along with Eucalyptus and Leucaena, due to better canopy coverage of the soil surface. Canopy coverage by Leucaena and Eucalyptus was restricted by harvesting, thus reducing their erosion and runoff control potential. Intercropping of cassava has great potential to decrease soil loss substantially. Soil erosion which is normally accelerated by deforestation of tropical rain forests can be successfully minimized by a proper combination of agricultural crops with forest species.


Tropical Erosion/Conservation

Since the 1950s, the residents of Leon, in western Nicaragua, suffered from choking duststorms that blanketed houses and streets with pesticide-laden dirt. Fifteen years ago, landowners rejected a soil-conservation program intended to help solve the problem, but now they have embraced a resurrection of the project that more directly involves them.

The duststorms began when the trees that once covered the flat lands of Leon were cleared to make way for extensive cotton cultivation. Because of the resulting severe wind erosion, soils soon lost their fertility, while the dust-laced air caused serious respiratory illnesses. Villagers planted rows of trees, which totaled 744 miles (1,200 kms.) and covered 99,000 acres (40,000 hectares). Leafy curtains impeded the dusty winds, while tree roots helped hold soils in place. Each curtain was 10 meters wide, made of five rows of trees, with 400 meters between curtains.They planted mostly eucalyptus because it grows quickly and is wind resistant.

But local landowners were less than thrilled that their property had been usurped for the windbreaks. Some burned the trees while others cut them down for firewood or simply bulldozed them to the ground. An inventory taken in 1986 showed that only 384 miles (620 kms.) of windbreaks remained intact. With a total of $1.4 million from Finland, the project was re-introduced in 1992, this time with local participation. Project technicians worked alongside farmers to cultivate organic soybeans, peanuts, sesame seeds, melons and watermelons instead of cotton. They have restored the tree curtains to the original size. Many farmers have received training in how to sustainably manage the windbreaks by harvesting just a few trees at a time. They can use the eucalyptus as a natural medicine, for firewood, and building material.


Animal Wastes/Erosion Management Practice

A BMP (best management practice) means a land-use practice, or combination of practices that is determined to be the most effective, practicable, economical, and technologically sophisticated means to better manage and utilize farm animal wastes and prevent or reduce soil erosion while at the same time protecting water quality.

A wide selection of voluntary, low-cost, easy-to-install BMP's that will help both small and large farm animal owners and breeders better manage, utilize, and dispose of manure are available. Also crops, vegetable, and nursery farm owners can increase soil fertility and soil water-holding campacity, and eliminate water drainage problems by installing BMP's.

BMP's for Manure Management and Soil Conservation Include:


United States Governments Involvement

Government involvement as well as involvement from other planning agency in preventing the effects of soil erosion is not only important, but essential. In 1935 the Soil Conservation Service was established. It administers a broad program of assistance in soil and water conservation on the land in cooperation with Conservation Districts. This service provides these kinds of assistance at the request of farmers, ranchers, and other landowners:

  1. Determining soil suitability guidelines based on the soil surveys for agriculture, housing, recreation, waste disposal, and road construction.
  2. Recommending Best Management Practices for erosion control and water protection.
  3. Designing sediment interception systems.
  4. Designing water facilities such as farm ponds.
  5. Planning recreational facilities.
  6. Designing terrace, irrigation, and drainage systems.
  7. Developing cropping systems to reduce erosion.
  8. Recommending pasture plantings.
  9. Developing range management guidelines.
  10. Promoting wildlife and woodland conservation.
  11. Supplying adapted planting materials for conservation planting.
  12. Promoting surface mine reclamation guidelines.
  13. Providing expertise on land use planning.

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This page was last updated on December 09, 2007