Here is a compilation of essays on ‘Soil Erosion’ for class 5, 6, 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Soil Erosion’ for school and college students.
Essay on Soil Erosion
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Essay Contents:
- Essay on the Meaning of Soil Erosion
- Essay on the Occurrence of Soil Erosion
- Essay on the Causes of Soil Erosion
- Essay on the Impact of Soil Erosion
- Essay on the Process of Soil Erosion
- Essay on the Measurement of Soil Erosion
- Essay on the Conservation of Soil Erosion
Essay # 1. Meaning of Soil Erosion:
All land use activities, particularly those which are poorly managed, involve destruction or disturbance, to a greater or lesser extent, of natural and semi-natural ecosystems. Almost invariably, however, it is those ecosystems, in equilibrium with their environment, which offer most effective protection to the soil that supports them.
A major consequence of ecosystem destruction and disturbance is that of soil degradation. This has been defined as the decline in soil quality caused through its misuse by human activity. More specifically it refers to the decline in soil productivity through adverse changes in nutrient status, organic matter structural stability and concentrations of electrolytes and toxic chemicals.
Soil degradation incorporates a number of environmental problems, some of which are interrelated, including erosion compaction, water excess and deficit, acidification, salinization and sodification and toxic accumulation of agricultural chemicals and urban/industrial pollutants.
In many instances, these have led to a serious decline in soil quality and productivity and it is only in recent decades that the finite nature of soil as a resource has become widely recognised. Soil degradation is not a new phenomenon. Archeological evidence suggests that it has been on-going since the beginning of settled agriculture several thousand years ago.
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The decline of many ancient civilizations, including the Mesopotamians of the Tigris and Euphrates valleys in Iraq, the Harappans of the Indus valley in Pakistan and the Mayans of Central America, was due in part to soil degradation.
More recently an event of major significance was the dustbowl which occurred in the Great Plains of the American Midwest during the 1930s.
At this time, intensive agricultural practices, employed in the eastern states, were transferred to the drier Midwest where the soils are lighter textured and more susceptible to erosion. A number of years of drought, combined with crop failure and destruction of the protective organic-rich topsoil, resulted in severe wind erosion.
According to the Global Assessment of Soil Degradation project, about 15 per cent of the global land area between 72°N and 57°S is degraded. Of this, an area slightly less than that of India (about 300 million hectares) is strongly degraded, largely as a result of deforestation (113 million hectares), inappropriate management of cropped land (83 million hectares) and overgrazing (75 million hectares).
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In recent decades, the global rate of soil degradation has increased dramatically and is likely to increase further as we approach the twenty-first century; in 1983 it was estimated at 5-7 million ha a-1 and is set to rise beyond 10 million ha a-1 by the year 2000.
The effects of soil degradation are not restricted to the soil alone, but have a number of off-site implications. Soil erosion, for example, is often associated with increased incidence of flooding, siltation of rivers lakes and reservoirs and deposition of material in low-lying areas.
These problems may be compounded in areas where infiltration capacity is reduced due to compaction, hard setting or induration of soils. Salinisation and sodification of soils are often associated with poor quality irrigation water while soil acidification is commonly linked with acidification and aluminium contamination of surface waters.
Leaching of fertilizers and pesticides from agricultural soils may also lead to contamination of surface and shallow ground waters.
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In addition, contamination of soils by urban and industrial pollutants, such as heavy metals and radionuclides, may lead to toxic accumulation in arable produce and in herbage for grazing animals, thus having important implications for human health.
The extent of soil degradation is influenced by a number of factors, many of which are interrelated, namely soil characteristics, relief, climate, land use and socio-economic and political controls (Fig. 23.1).
In many studies of soil degradation and its wider environmental implications, the socio-economic and political controls are often overlooked, or at least not examined in any detail, perhaps because of the difficulties associated with the collection of reliable and comparable data.
Increasingly, however, these controls on land use systems are being viewed as central to the issue of soil degradation, particularly in the developing world.
Management of soil degradation, whether at a global, regional or local scale, is clearly a complex issue and represents one of our most challenging environmental problems.
Emphasis should be placed on sustainable, rather than exploitative land use practices; this theme was highlighted by the World Soil Charter which called for a commitment by governments, agencies and land-users to ‘manage the land for long term advantage rather than short term expediency’ .
The problem requires a holistic, multidisciplinary approach involving the collaborative and coordinated efforts of ecologists, agronomists, soil scientists, hydrologists, engineers, sociologists and economists. Moreover, the involvement of government and non-government organisations, aid agencies and the farmers themselves is essential to the success of research and development in this area.
Such involvement should facilitate the implementation of education, training and incentive programmes. Imposition from above of high-technology, high-cost solutions by technical experts from developed countries is certainly not the answer in the developing world.
Inevitably, such solutions are not economically viable and low-technology, low-cost options—such as low external input agriculture, agroforestry and social forestry—are often the only answer.
Hence, the approach to soil conservation has shifted in recent years from a rather techno centric standpoint to a more eco-centric position. Central to this approach are the concepts of land husbandry and sustainable development, which place emphasis on the land-users themselves rather than on the technical experts and advisors.
This chapter aims to examine a selection of the most pressing soil degradation problems and, in each case, the causal factors, on and off site effects and management strategies will be considered.
Essay # 2. Occurrence of Soil Erosion:
Soil erosion occurs when the rate of removal of soil by water and/or wind exceeds the rate of soil formation. Generally, rates of soil formation are very low, with profiles developing at a rate of about 1 cm every 100-400 years; assuming an average bulk density of 1.33g cm-3, this equates to about 0.3 – 1.3 t ha-1 a-1.
It is important to differentiate between natural or background erosion and erosion which has been accelerated largely as a result of human activity.
Background erosion rates are often similar to rates of soil formation at < 1.0 t ha-1 a-1, although in mountainous areas they may be considerably higher. In contrast, rates of accelerated erosion commonly exceed 10 t ha-1 a-1 and sometimes exceed 100t ha-1 a-1
Some of the highest soil erosion rates have been observed in the Loess Plateau area of China and in the Himalayan foothills of Nepal, where values in excess of 200 t ha-1 a-1 have been recorded. Similarly, in India, gully erosion results in a loss of about 8,000 ha of land per year.
The extent of soil erosion is governed by a number of factors. Those of particular importance include erosivity of the eroding agent, erodibility of the soil, slope steepness and length, land use practices and conservation strategies.
These factors are summarised in the Universal Soil Loss Equation which has been used widely in the modelling and prediction of soil erosion e.g., Colby-Saliba:
E = R.K.L.S.C.P.
where, E = mean annual soil loss, R = rainfall erosivity index, K = soil erodibility index, L = slope length, S = slope steepness, C = cropping factor which represents the ratio of soil loss under a given crop to that from bare soil, and P = conservation practice factor which represents the ratio of soil loss where contouring and strip-cropping are practiced to that where they unused.
Although widely used, this model has been the subject of extensive criticism. For example, it assumes that a vegetation cover is always protective which is not necessarily the case; erosion on land with a good cover of crops planted in rows can be greater than on land which is sparsely vegetated. It is also water erosion based and cannot be used in areas affected extensively by wind erosion.
More specifically, it focuses on rill and inter-rill erosion and is not easily applied to areas where gully and stream bank erosion are widespread. Its universal nature has also been questioned particularly in terms of its application to tropical soils.
Furthermore, it should be emphasised that this model does not consider the wide range of socio-economic and political factors which play a crucial role in terms of their influence on the degree of soil erosion which will be examined later. Alternative models include SLEMSA (Soil Loss Estimator for Southern Africa) and CREAMS (Chemicals Run-off and Erosion Arising From Agricultural Management Systems).
Land use is perhaps the most significant factor influencing soil erosion, for two main reasons. First, many land use practices leave the soil devoid of a protective vegetation cover, or with only a partial cover, for significant periods of time and second, they involve mechanical disturbance of the soil.
Specific aspects of land use often associated with accelerated soil erosion include expansion and intensification of arable cultivation, overgrazing, deforestation, certain forestry practices, site clearance in preparation for urban and industrial construction and a number of recreational activities such as walking and skiing.
Arable cultivation has expanded and intensified dramatically in recent decades. Relatively steep slopes, formerly covered by grass or tress, have been converted to arable cropping, while an increased use of heavy agricultural machinery has resulted in compaction of the soil. This, in turn, has led to reduced infiltration capacity, particularly along wheel tracks, thus resulting in increased surface run-off and erosion.
Similarly, increased reliance on tillage activities, throughout the cropping cycle, has rendered soils more susceptible to erosion. This problem has been compounded by the decline in levels of soil organic matter and hence structural stability, largely in response to increased use of inorganic fertilizers.
In addition, the tendency to increase field sizes on arable land has meant that there are fewer physical breaks and barriers in the landscape, such as tree lines, hedgerows and walls, to restrict erosion. Susceptibility to erosion is further increased if land is cultivated with the slope rather than parallel to the contours.
Overgrazing is particularly common in drought-affected parts of the developing world, such as the Sahel region of sub-Saharan Africa and the rangelands and communal lands of eastern and southern Africa.
In a study of the impact of grazing on soils of the Savanna region of Nigeria, for example, Aweto and Adejumbobi (1991) attribute enhanced surface run-off and erosion to compaction of the soil and destruction of the protective vegetation cover by grazing animals and to the adoption of inappropriate burning strategies.
Deforestation, largely for logging and wood fuel purposes, is also common in many parts of the developing world.
Trees are well-known for their ability to protect soils from erosion, particularly on steeply sloping terrain. Their root systems and the organic material which they supply help to stabilise the soil, while water uptake and canopy interception serve to reduce the frequency and intensity of surface run-off.
In addition to deforestation, many forestry practices are associated with accelerated soil erosion, including the needle leaf forestry programmes which have become widespread in many areas of upland Britain. Here, erosion is most serious during the pre-planting stages of land preparation and drainage and after harvesting.
In relation to urban and industrial land use, construction and associated disturbance of land may lead to increased soil erosion. Even certain recreational activities have been implicated in this problem, including walking and skiing.
A number of socio-economic and political factors have been associated with accelerated soil erosion, particularly in the developing world. These include population pressure, skewed land resource distribution; poverty and marginalization, increasing demand for wood fuel, inappropriate land tenure and farm policies, small size of land-holdings and poor infrastructure.
In many developing countries, population growth is rapid and the demand for agricultural land and wood fuel is ever increasing (Table 23.4).
Furthermore, agricultural systems are characterised by a skewed land resource distribution where a minority of affluent and powerful landowners control a majority of the land area.
The poorest farmers are thus forced onto marginal land, which is particularly susceptible to erosion, and often end up in a vicious spiral of debt. Rural-urban migration, abandonment of land and increased soil erosion are often responsible to this poverty trap situation (Fig. 23.2).
In many parts of the developing world, large areas of land are utilised for mono-cultivation of cash crops, which are not necessarily best-suited to soil conditions, rather than for indigenous mixed food cropping. Such commercial pressure on agricultural systems, as well as contributing to the problem of marginalization discussed above, has a detrimental effect on soil quality and is unlikely to be sustainable in the long term.
There is also little political support in terms of education, training and incentive schemes to encourage farmers to adopt more sustainable land use practices. The establishment of appropriate and comprehensive soil conservation and land husbandry programmes is further hindered by the small size of land-holdings and the large number of farmers involved (Table 23.5).
The on and off-site effects of soil erosion are considerable. At the global scale, it is estimated that unless soil conservation measures are introduced on all cultivated land, 544 million ha of potentially productive rain-fed crop land will be lost and agricultural production expected to decrease by almost 20 per cent, by the year 2000-2005.
Undoubtedly, these effects will be felt most severely in those developing countries which are least able to cope with the problem. It should be noted that the deterioration in soil productivity is disproportionate to the amount of soil eroded, as it is the nutrient rich and structure- supporting constituents in the topsoil which are lost most readily.
Essay # 3. Causes of Soil Erosion:
These are as follows:
(i) Overcropping:
Overcropping causes the soil to deteriorate when too many crops are grown on the same land without the farmer replacing lost mineral and organic material. In natural conditions, as plants grow, they extract the valuable mineral and organic plant nutrients from the soil; when they die, they decay and release their nutrients, returning them to the soil which is thus enriched for other plants that come after them.
But when men cultivate crops, they harvest them and carry the crops elsewhere to be sold or consumed. There is no replacement at all. If the farmer year after year, grows cotton which is very exhaustive of nitrates, and does not add any manure or fertilizers, the soil is bound to become poorer until the farm has to be abandoned.
Overcropping may occur in several ways:
(a) Monoculture:
This is the growing of a single type of crop, year after year, such as cotton or wheat. The crop is constantly using up particular types of minerals from the soil which it needs. As a result some minerals in the soil may be completely exhausted and fertility may decline if fallow periods, fertilizers or crop rotations are not used to balance soil properties.
(b) Multicropping:
This is the constant use of the land for several crops every year. If there is not a constant supply of fertilizer this quickly exhausts the soil and yields rapidly decline.
(c) Shifting cultivation:
This type of cultivation of forest clearings can be very harmful. The destruction of the trees by fire means that the soil is no longer protected from the full force of heavy tropical rain, nor is it consolidated and held together by plant roots. It is therefore quickly washed away. After the ladangs are abandoned the forest is allowed to grow again, and, if the plot is not cleared again for a long time (about 20 years), the rest or fallow period is long enough for the soil to regain its humus and mineral content.
If, however, as usually happens, the plots are re-cleared after only a few years or one plot is occupied for too many years, the soil cannot recuperate and it becomes permanently infertile. It may be eroded into deep gullies or invaded by lalang grass and is thus made useless either for farming or for forest.
(ii) Overgrazing:
Animal grazing is dependent upon either natural or man-sown grasses and herbs, which are eaten by the cattle, sheep, goats or horses. The number of animals that can be grazed depends on the carrying capacity of the pasturage, that is the number of animals which can graze on the pasture without completely killing the grasses or other plants.
If the number of animals is within the carrying capacity, the grass is able to grow again, but if there are too many animals it may not have sufficient time to recover and may be killed. If this happens the vegetative cover becomes too thin to protect the soil and rain and wind are able to erode the soil.
This in turn reduces the amount of grass that can grow in the area. In parts of Mediterranean Europe, West and East Africa and India, overgrazing by cattle, or worse still by sheep or goats which nibble down every bit of grass, has caused acute soil erosion.
(iii) Deforestation:
When men remove the natural forest cover of an area either for agriculture or for timber this usually exposes the area to soil erosion because the soil is no longer protected by the leafy canopy of the forest from heavy rain or strong winds. The bad effects of deforestation are worst when all the trees, even the smallest, are removed and when new seedlings are not planted to replace the felled timber.
(iv) Slope Cultivation:
Soil erosion is always enhanced when the cleared area of land is on a steep slope, because this allows gully erosion to take place. The soil on slopes, too, is easily moved by gravity when it is loosened. The effects of shifting cultivation, overgrazing and deforestation are all worse on steeply sloping land.
Where cultivation takes place on steep slopes erosion is greatly aggravated if plants are arranged slope-wise, i.e. in rows up and down the hill slope. This practice of slope-wise cultivation produces ready-made channels down which rain-water can flow carrying away the topsoil.
(v) Cultivation of Dry Areas:
In semi-arid areas the cultivation of marginal agricultural lands may lead to erosion because the removal of the natural vegetation and the ploughing of the land loosens the soil and this enables the wind to blow it away. In marginal areas such as this, special dry-farming techniques have to be adopted unless a ‘Dust Bowl’ situation is to arise.
Essay # 4. Impact of Soil Erosion:
The rapid erosion of soil by wind and water has been a problem ever since land was first cultivated. The consequences of soil erosion occur both on- and off-site.
On-site effects are particularly important on agricultural land where the redistribution of soil within a field, the loss of soil from a field, the break-down of soil structure and the decline in organic matter and nutrient result in a reduction of cultivable soil depth and a decline in soil fertility. Erosion also reduces available soil moisture, resulting in more drought-prone conditions.
The net effect is a loss of productivity which, at first, restricts what can be grown and results in increased expenditure on fertilizers to maintain yields, but later threatens food production and leads, ultimately, to land abandonment. It also leads to a decline in the value of the land as it changed from productive farmland to wasteland.
Offsite problems result from sedimentation down stream or downwind which reduces the capacity of rivers and drainage ditches, enhances the risk of flooding, blocks irrigation canals and shortens the design life of reservoirs. Many hydroelectricity and irrigation projects have been ruined as a consequence of erosion.
Sediment is also a pollutant in its own right and, through the chemicals adsorbed to it, can increase the levels of nitrogen and phosphorus in water bodies and result in eutrophication.
Essay # 5. Process of Soil Erosion:
Soil erosion is a two-phase process, consisting of the detachment of individual particles from the soil mass and their transport by erosive agents such as running water and wind. When sufficient energy is no longer available to transport the particles, a third phase—deposition—occurs.
Rain splash is the most important detaching agent. The soil is also broken up by weathering processes, both mechanical, by alternate wetting and drying, freezing and thawing and frost action and biochemical. Soil is disturbed by tillage operations and by the trampling of people and livestock. Running water and wind are further contributors to the detachment of soil particles.
All these processes loosen the soil so that it is easily removed by the agents of transport. The severity of erosion depends upon the quality of material supplied by detachment and the capacity of the eroding agents to transport it.
There are a number of factors that control erosion:
1. Erosivity of the eroding agent;
2. Erodibility of the soil;
3. Slope of the land; and
4. Nature of the plant cover.
In the field, soil erosion status may be surveyed and data are recorded as per proforma (Table 23.6) for further interpretation.
Essay # 6. Measurement of Soil Erosion:
Those designed to determine soil loss from relatively small sample areas or erosion plots often as part of an experiment and those designed to assess erosions over a larger area such as a drainage basin.
In erosion plot, a standard size of 22 m long and 1.8 m wide are used. The plot edges are made of sheet metal, wood or any material which is stable, does not leak and is not liable to rust. At the downslope end is positioned a collecting trough or gutter, covered with a lid to prevent the direct entry of rainfall, from which sediment and runoff are channelled into collecting tanks.
For large plots or where run-off volumes are very high, the overflow from a first collecting tank is passed through a divisor which splits the flow into equal parts and passes one part, as a sample, into a second collecting tank. A flocculating agent is added to the mixture of water and sediment collected in each tank.
The soil settles to the bottom of the tank and the clear water is then drawn-off and measured. The volume of soil remaining in the tank is determined and a sample of known volume is taken for drying and weighing. The sample weight multiplied by the total volume gives the total weight of soil in the tank.
The total soil loss from the plot is the weight of the soil in the first tank plus, assuming one-fifth of the overflow from the first tank passes through the divisor into the second tank, five times the weight of soil in the second tank.
Where automatic sediment sampling occurs, the sediment concentration is determined for each sample. Since the time that each sample was taken during the storm is known, the data can be integrated over time to give a sediment graph.
Investigation of sediment production in a catchment or drainage basin must be carried through an elaborate layout of erosion plot investigation in the stream slopes of various orders.
Essay # 7. Conservation of Soil Erosion:
Soil conservation design most logically follows a sequence of events (Fig. 23.3) beginning with a thorough assessment of erosion risk, followed by designing a sound land use plan based on what the land is best suited for under present or proposed economic and social conditions, land tenure arrangements and production technology and what is compatible with the maintenance of environmental stability.
However, the approach of soil conservation varies from place to place and also based on type of land use. For instance, erosion control in cultivated land is dependent upon good management which implies establishing sufficient crop cover and selecting appropriate tillage practices.
Thus soil conservation relies strongly on agronomic methods combined with sound soil management whilst mechanical measures play only a supporting role. On the whole, the conservation strategies are aimed at establishing and maintaining good ground cover.
The details are given in Table 23.7:
Further, it is recognised that strategies for soil improving traditional systems instead of imposing entirely new techniques from outside and on enhancing land husbandry (Fig. 23.4, Table 23.7).
In addition there are a number of mechanical field practices used to control the soil erosion.
Three methods are normally employed in conjunction with agronomic measures:
1. Contouring i.e., carrying out ploughing, planting and cultivation on the contour can reduce soil loss from sloping land compared with cultivation up and down the slope.
2. Contour bunds i.e., these are earth banks 1.5 – 2m wide thrown across the slope to act as a barrier to run-off, to form a water storage area on their upslope side.
3. Terraces—these are earth embankments constructed across the slope to intercept surface runoff and convey it to a stable outlet at a non-erosive velocity and to shorten slope length.
4. Waterways—to convey run-off at a non-erosive velocity to suitable disposal part viz., diversion ditches, terrace channels, grass waterways etc.
5. Stabilisation structures—this is a specialised structure build up to produce small dams (0.4 to 2 meter height) by locally available materials for gully erosion control.