Why is erosion a problem

The amount and rate of surface runoff can affect erosion and sediment transport. Thus, soil conservation practices are important in reducing soil erosion. Improving the soil infiltration rate, resulting in less surface runoff, can lead to reduction of soil erosion.

Agronomic, cultural, or structural practices are available for controlling soil erosion. Structural practices involve physical changes in the shape and topography of the land. All these practices are not mutually exclusive.

Some situations may require both management and structural changes, where the topography is highly complex. In other situations, erosion control can be achieved by implementing a single practice, where the erosion is minimum, such as the establishment of grassed waterways. The most effective way to control erosion is to maintain a permanent surface cover on the soil surface, such as pasture or meadow.

Therefore, areas that are highly susceptible to water or wind erosion need to be considered for soil conservation programs. Soil losses in Iowa due to water erosion and surface runoff can contribute a great deal to surface water quality concerns. Many studies indicate that soil erosion results in large decreases in soil productivity.

In a study conducted at Iowa State University on 40 soil associations, Craft and coworkers Proceedings of the National Symposium on Erosion and Soil Productivity , reported that the impact of soil erosion on soil productivity was largely determined by subsoil properties because they effect root growth, soil water availability, and plow layer fertility.

Thus, the loss of the topsoil can have considerable impact on yield, where nutrient availability, root growth environment, and soil water availability are essential for plant development. In soils with unfavorable subsoil conditions, erosion can have a large effect on productivity, if the plow layer soil fertility is not restored.

Plant residue management is another way of controlling soil erosion by intercepting raindrops, thereby reducing surface runoff and protecting soil surface particle detachment by raindrop impact. Crop residue can provide an excellent soil cover after harvest and enhance snow harvesting during the off season, improve soil water intake by preventing soil surface sealing due to raindrop impact, and consequently, reduce surface runoff.

Equally important in minimizing soil erosion is the adoption of a cropping system along with conservation tillage practices such as no-till, strip-till, and ridge-till.

In the USA, soil erodes at an average rate of 9 to 12 tonnes per acre per year. Soil erosion increased far more.

By , USA farmers were losing an estimated six tons of soil for every ton of grain they produced. Almost half of America's cropland is losing soil faster than it can be replaced. A survey measured the annual loss at 3.

In developing countries erosion rates per acre are twice as high as the USA, partly because population pressure forces land to be more intensively farmed. Worldwide, farmers are losing an estimated 24 billion tonnes of topsoil each year, roughly the amount of topsoil covering all of Australia's wheatlands. New topsoil is constantly being formed, of course, but at nature's leisurely pace of about 1.

The difference between creation and loss represents an annual loss of 7. Erosion has now reached unprecedented proportions and, should it continue at the current rate, one-third of the world's arable land will be depleted within the next 20 years. Perhaps the grimmest soil erosion report in recent years came in when a dispatch from the USA Embassy in Addis Ababa indicated that an estimated 1 billion tonnes of topsoil were washing down from Ethiopia's highlands each year, presaging the recurrent famines that have followed.

In parts of northern Ethiopia, as for cropland degradation throughout the Third World, there is simply not enough topsoil left to sustain even subsistence-level farming. According to a report, nearly two-thirds of Haiti's 6 million people depended on agriculture for a living. Over the years they have burnt trees and bushes to make room for crops — and to produce charcoal, which they sell.

Farmers have exhausted the land by planting too many crops too often. The lack of trees was wearing away the topsoil, which means that even fewer things would grow in the years ahead. With two percent of its forests left, more than one-third of the country was so affected by topsoil loss as to be unreclaimable for farming. Soil washed into the streets of Port-au-Prince had to be cleared with bulldozers in the rainy season. It is currently published as a searchable online platform with profiles of world problems, action strategies, and human values that are interlinked in novel and innovative ways.

These connections are based on a range of relationships such as broader and narrower scope, aggravation, relatedness and more. By concentrating on these links and relationships, the Encyclopedia is uniquely positioned to bring focus to the complex and expansive sphere of global issues and their interconnected nature. Recognizing that international associations are generally confronting world problems and developing action strategies based on particular values , the initial content was based on the descriptions, aims, titles and profiles of international associations.

Partially incorporated residues and residual roots are also important as these provide channels that allow surface water to move into the soil. The effectiveness of any protective cover also depends on how much protection is available at various periods during the year, relative to the amount of erosive rainfall that falls during these periods.

Crops that provide a full protective cover for a major portion of the year e. Crop management systems that favour contour farming and strip-cropping techniques can further reduce the amount of erosion.

The potential for soil erosion by water is affected by tillage operations, depending on the depth, direction and timing of plowing, the type of tillage equipment and the number of passes. Generally, the less the disturbance of vegetation or residue cover at or near the surface, the more effective the tillage practice in reducing water erosion.

Minimum till or no-till practices are effective in reducing soil erosion by water. Tillage and other practices performed up and down field slopes creates pathways for surface water runoff and can accelerate the soil erosion process.

Cross-slope cultivation and contour farming techniques discourage the concentration of surface water runoff and limit soil movement. Sheet erosion is the movement of soil from raindrop splash and runoff water. It typically occurs evenly over a uniform slope and goes unnoticed until most of the productive topsoil has been lost.

Deposition of the eroded soil occurs at the bottom of the slope Figure 3 or in low areas. Lighter-coloured soils on knolls, changes in soil horizon thickness and low crop yields on shoulder slopes and knolls are other indicators.

Figure 3. The accumulation of soil and crop debris at the lower end of this field is an indicator of sheet erosion. Rill erosion results when surface water runoff concentrates, forming small yet well-defined channels Figure 4. These distinct channels where the soil has been washed away are called rills when they are small enough to not interfere with field machinery operations.

In many cases, rills are filled in each year as part of tillage operations. Figure 4. The distinct path where the soil has been washed away by surface water runoff is an indicator of rill erosion.

Gully erosion is an advanced stage of rill erosion where surface channels are eroded to the point where they become a nuisance factor in normal tillage operations Figure 5. There are farms in Ontario that are losing large quantities of topsoil and subsoil each year due to gully erosion. Surface water runoff, causing gully formation or the enlarging of existing gullies, is usually the result of improper outlet design for local surface and subsurface drainage systems.

The soil instability of gully banks, usually associated with seepage of groundwater, leads to sloughing and slumping caving-in of bank slopes. Such failures usually occur during spring months when the soil water conditions are most conducive to the problem. Gully formations are difficult to control if corrective measures are not designed and properly constructed. Control measures must consider the cause of the increased flow of water across the landscape and be capable of directing the runoff to a proper outlet.

Gully erosion results in significant amounts of land being taken out of production and creates hazardous conditions for the operators of farm machinery. Figure 5. Gully erosion may develop in locations where rill erosion has not been managed. Natural streams and constructed drainage channels act as outlets for surface water runoff and subsurface drainage systems. Bank erosion is the progressive undercutting, scouring and slumping of these drainageways Figure 6.

Poor construction practices, inadequate maintenance, uncontrolled livestock access and cropping too close can all lead to bank erosion problems. Figure 6. Bank erosion involves the undercutting and scouring of natural stream and drainage channel banks. Poorly constructed tile outlets also contribute to bank erosion.

Some do not function properly because they have no rigid outlet pipe, have an inadequate splash pad or no splash pad at all, or have outlet pipes that have been damaged by erosion, machinery or bank cave-ins. The direct damages from bank erosion include loss of productive farmland, undermining of structures such as bridges, increased need to clean out and maintain drainage channels and washing out of lanes, roads and fence rows.

The implications of soil erosion by water extend beyond the removal of valuable topsoil. Crop emergence, growth and yield are directly affected by the loss of natural nutrients and applied fertilizers. Seeds and plants can be disturbed or completely removed by the erosion.

Organic matter from the soil, residues and any applied manure, is relatively lightweight and can be readily transported off the field, particularly during spring thaw conditions. Pesticides may also be carried off the site with the eroded soil. Soil quality, structure, stability and texture can be affected by the loss of soil. The breakdown of aggregates and the removal of smaller particles or entire layers of soil or organic matter can weaken the structure and even change the texture.

Textural changes can in turn affect the water-holding capacity of the soil, making it more susceptible to extreme conditions such as drought. The off-site impacts of soil erosion by water are not always as apparent as the on-site effects. Eroded soil, deposited down slope, inhibits or delays the emergence of seeds, buries small seedlings and necessitates replanting in the affected areas. Also, sediment can accumulate on down-slope properties and contribute to road damage. Sediment that reaches streams or watercourses can accelerate bank erosion, obstruct stream and drainage channels, fill in reservoirs, damage fish habitat and degrade downstream water quality.

Pesticides and fertilizers, frequently transported along with the eroding soil, contaminate or pollute downstream water sources, wetlands and lakes. Because of the potential seriousness of some of the off-site impacts, the control of "non-point" pollution from agricultural land is an important consideration.

Wind erosion occurs in susceptible areas of Ontario but represents a small percentage of land — mainly sandy and organic or muck soils.

Under the right conditions it can cause major losses of soil and property Figure 7. Figure 7. Wind erosion can be severe on long, unsheltered, smooth soil surfaces. Soil particles move in three ways, depending on soil particle size and wind strength — suspension, saltation and surface creep.