Read this essay to learn about soil erosion in India. After reading this essay you will learn about: 1. Definition and Occurrence of Soil Erosion 2. Causes of Soil Erosion 3. Soil Erosion by Wind 4. Soil Erosion by Water 5. Soil Erosion Due to Pollutions 6. Magnitude of Soil Erosion Problem 7. Effects of Soil Erosion 8. Conservation Measures.
List of Essays on Soil Erosion in India
Essay Contents:
- Definition and Occurrence of Soil Erosion
- Causes of Soil Erosion
- Soil Erosion by Wind
- Soil Erosion by Water
- Soil Erosion Due to Pollutions
- Magnitude of Soil Erosion Problem
- Effects of Soil Erosion
- Conservation Measures for Preventing Soil Erosion
Essay # 1. Definition and Occurrence of Soil Erosion:
Soil erosion is defined as the detachment and transportation of soil mass from one place to another through the action of wind, water in motion or by the beating action of rain drops. Erosion extensively occurs in poorly aggregated soils (low humus) and in a higher percentage of silt and very fine sand. Erosion increases when soil remains bare or without vegetation.
Soil erosion occurs when the rate of removal of soil by water/and 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.
It is important to differentiate between natural or backward 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 although in mountainous areas they may be considerably higher.
Some of the highest soil erosion rates have been observed in the less plateau areas of China and in the Himalayan foothills of Nepal. In India gully erosion results in a loss of about 8000ha of land per year.
Materials can be lost from soils in four main forms – gases, solutes, particulate material and vegetation removal. As in the case of additions, the processes involved can usefully be divided into surface and subsurface categories.
Surface losses include gases which are produced during organic matter decomposition and lost to the atmosphere, solutes which are taken up as nutrients by vegetation and then lost when the vegetation is removed, for example by harvesting of crops or removal of trees, particulate material which is lost by water or wind erosion, and the upper parts of profiles which may be removed by erosion or human activity.
In the case of gases and solutes, the significance of losses via the surface will depend on the extent to which they are dissolved and lost by subsurface drainage; which in turn will depend on climate and land use.
Removal of particulate material by wind will be most effective in the case of soils with a high silt or fine sand content, as this size of maternal is more easily entrained than larger, heavier particles or small clay particles which resist entrainment due to their greater aggregation.
Organic matter is also prone to wind erosion, and its lower density relative to mineral material means that larger particles can more easily be carried. Low moisture content, poor aggregation and sparse vegetation covers will also enhance susceptibility to erosion. Small particles (< 0.05mm in diameter) are transported by aerial dispersion and may be carried to elevations of several thousand metres.
Particles of intermediate size (0.05 – 0.5 mm) are transported within a metre or so of the ground surface by the process of saltation. In contrast, large particles (> 0.5 mm) are moved along the ground, largely as a result of impacts from saltating particles, by the process of creep.
Saltation is the most important process of wind erosion in terms of the quantity of material moved, and it is estimated that 55-72% of wind eroded particles are transported in this way.
In the case of erosion by water, soils with weak aggregation and low vegetation covers are with weak aggregation and low vegetation covers are particularly susceptible because the aggregates can be easily broken down by direct raindrop impact.
This can also result in surface compaction and sealing to form a crust which may be several mm in thickness which impedes infiltration, therefore, enhancing the loss of material by surface runoff.
Erosion of land by wind and water has destroyed thousands of hectares of good agricultural land in many countries. The best known of such disasters is the “dust bowl” which formed in parts of Central United States of America in the 1920’s.
It developed following the widespread practice of continuous arable cropping of land which had previously been in grassland or forest. More recently, erosion has given problems following ploughing up of old grassland on the plains of the erstwhile USSR. Some pundits point to the occurrence of occasional wind erosion on peat soils and on some sand lands, claiming they are the beginning of such troubles.
Erosion losses can also occur, for example by glacier ice, if there is a major change in environmental conditions. Losses of material by human activity can occur in many ways, but the most common are associated with the removal of top-soil for use as a resource or during construction.
For example, organic rich soil may be extracted to improve the cultivation capabilities of soil elsewhere. Removal of soil is also often associated with the construction of roads and buildings, or with landscaping programmes.
Subsurface losses can occur in solute or solid form and can involve any of the products of addition and transformation, along with those materials undergoing transfer where conditions for total re-deposition within the soil do not occur.
The extent of solute outputs will clearly depend on the solubility of the material involved, along with factors such as temperature, which will control the rate at which reactions occur, and the speed of water movement, which will determine the time available for reactions to occur.
Material lost in a solid particulate form will only occur with any significance in solids containing large pores or other forms of passage ways. In coarse- textured or un-compacted soils, pore space may be sufficiently large to allow material to move out of the soil and into drainage channels, but particulate losses are more usually associated with the development of soil pipes, whose diameter can range from a few centimetres up to several metres.
These are found in soils which experience cracking, due to the occurrence of either highly expandable clay minerals such as smectite or high organic contents, and which also contain a subsurface layer of restricted permeability. Soil pipes allow large volumes of water to be moved rapidly through them, resulting in the removal of both solid particles and dissolved material.
The extent of soil erosion is governed by a number of factors. Those of particular importance include erosivity of the eroding agent, erodability of the soil, slope steepness and length, land use practices and conservation strategies.
Soil erosion, the removal of soil by water and wind, is the most common and extensive. Natural or geologic erosion ranges from very little in undisturbed lands to extensive in steep arid lands. Geological erosion takes place, as a result of the action of water, wind, gravity and glaciers and it takes place, at such slow rates that the loss of soil is compensated for the formation of new soil under natural weathering processes.
It is sometimes referred to as normal erosion. Accelerated erosion caused by the disturbances of people (cutting forests, cultivating lands, constructing roads and buildings etc.) and is increasing as the population increases. In this erosion, the removal of soil takes place at a much faster rate than that of soil formation.
It is also referred to as abnormal erosion. It is impossible to stop all erosion completely, but can be minimised. Techniques to control water and wind erosion usually result in maintaining or increasing soil productivity also.
Soil erosion today poses grave threat to the agriculture. So it has been identified as the great menace to soil fertility. Any exposed soil-covered region in India is subjected to soil erosion. The effect of any external force directly hampers the equilibrium condition of soil.
Removal of the upper part of soil, i.e., soil erosion, is detrimental to plant growth. Major forces that accelerates the rate of soil erosion are: excess rainfall, frequent floods, alternate glaciation and de-glaciation, continuous wind blowing etc.
Soil erosion may be sub-divided into several groups:
i. Sheet erosion:
It removes the top layer of soil as sheets. It is very widespread in peninsular India and desert region of Rajasthan.
ii. Gully erosion:
When gullies extend vertically, horizontally or in both the direction, those wash away soil. It is very severe in Uttar Pradesh, Bihar, Maharashtra, Andhra Pradesh and Himalaya.
iii. Rill erosion:
When small rivulets, distributaries and small water sources extends, removal of soil takes place. Increased rill erosion is ultimately converted into large scale gully erosion.
These factors are summarized in the universal soil loss Equation:
E = R.K.L.S.C.P.
Where E = Mean annual soil loss
R = rainfall erosivity index
K = Slope erodability
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.
P = Conservation practice factor which represents the ratio of soil loss where contouring & Strip cropping are practiced to that where they are not.
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. Its universal nature has also been questioned particularly in tens of its application to tropical soils. Erosivity is a measure of the potential of the eroding agent to erode and is commonly expressed in terms of kinetic energy.
Essay # 2. Causes of Soil Erosion:
The supreme cause of excessive erosion is removal of vegetational cover from the soil.
The important causes are:
i. Deforestation:
The destruction of forest covers leads to increased run-off of rain water and diminished storage in the soil. The structure of the soil suffers due to lack of organic matter thus run-off increases. The water develops power enough to cause devastating floods. In natural forest, when rain falls gently, the whole is absorbed and violent flood is lessened.
ii. Destruction and Overgrazing of Pastures:
A properly managed, lightly grazed pasture might form a permanent protection to the soil because it provides an efficient cover for preventing erosion and reducing run-off. But when there is overgrazing by cattle, goats and sheep, the soil becomes uncovered as the grass overgrazed.
Raindrops begin to fall directly on the soil puddling the surface and clogging up the pores with mud, infiltration into the soil is reduced and the run-off of the water increases, thus causing soil erosion.
iii. Shifting Cultivation:
Man’s ruthless destruction of the forest for shifting cultivation has also decreased the area under forest. Shifting or jhuming cultivation is chiefly practiced by the tribal communities for raising food for them.
According to this system of farming, the forests are cleared and cultivated for 2-3 years. After two or three year’s crop, the soil is exhausted and then another felling of forest takes place and the first is abandoned for 5-15 years.
iv. Faulty Methods of Cultivation:
When the virgin land is ploughed and naked soil is exposed to the rain the loss of the fertile soil is enormous, particularly on the steeper slopes. On the slopes or hills, tillage practices along the slope increases run-off and erosion.
Essay # 3. Soil Erosion by Wind:
Wind erosion often known as ‘blowing’, starts with a process known as ‘saltation’, which is a sort of jumping motion of the smallest, most erodible particles or aggregates of soil. Particles which become airborne in gusts of wind fall gradually back to the ground in a trajectory rather like that of a bullet after covering a distance of three or four metres.
The impact of these particles hitting the ground moves other particles of a similar size and larger particles. The larger particles slide and roll along the surface in a process known as ‘avalanching’ until stopped by ditches or hedges while finer material is projected higher into the air to form dust clouds.
The erosion process sorts the soil particles according to their size, moving the coarser ones only short distances, while depositing the finest much greater distances, often as much as kms. downwind. With successive blows the eroded soil becomes more coarse as most of the fine material is blown away.
The velocity of the wind at the soil surface is one of the most important factors affecting erosion. A speed of about 30-40 km/hr is needed before blowing starts. Moist soils are much less liable to erode than dry ones because moist particles stick to one another to some extent.
A warm dry wind which rapidly dries out the surface is much more liable to give trouble than a cool humid one, and soils in low- rainfall areas are more susceptible to blowing than soils in wet areas. Flat or gently undulating land is more susceptible to erosion than hilly country which slows down the speed of the wind.
Bare land is much more susceptible than cropped land because the stems and leaves of plants slow down the surface wind speed; and the roots of closely drilled crops, such as cereals, tend to bind the soils together.
The roots of widely spaced row crops, such as sugar beat, give the least protection. A loose surface with a fine filth gives the greatest opportunity for the wind to start erosion, and a coarse cloudy surface is least susceptible.
Soil erosion by wind has caused an accumulation of eroded particles in loess, a type of soil which makes up some of the world’s most fertile and productive regions. Soil conditions conducive to wind erosion are most commonly found in arid and semi-arid areas where rainfall is insufficient and no vegetative cover on the land.
The most serious damage caused by wind erosion is the change in soil texture. Since the finer soil particles are subject to movement by wind, wind erosion gradually removes silt, clay and organic matter from the top soil, leaving the coarser soil material.
Movement of Soil Particles by Wind:
Movement of soil particles is caused by wind forces exerted against or parallel to the surface of the ground. The erosive wind is turbulent at all heights except in a paper thin zone along the surface layer where the flow is smooth or laminar.
As wind moves over the surface, a gradient in velocity exists, the velocity is lowest near the ground and increases in proportion to the logarithm of the height above the surface. Movement of soil particles are shown in Fig. 27.2
Wind erodes the soil in three steps:
Initiation of movement, transport either in the air or along the surface, and deposition of soil in a new site. Each step is influenced by the condition of air, ground surface and the soil. After such movement is started, the soil particles are carried by the wind in three types namely saltation, suspension and surface creep.
i. Saltation:
Saltation is a process of soil movement in a series of bounces or jumps. Soil particles having sizes ranging from 0.05 to 0.5 mm generally move in this process. Saltation movement is caused by the pressure of the wind on the soil particle, and collision of a particle with other particles. The height of the jumps varies with the size and density of the soil particles, the roughness of the soil surface, and the velocity of the wind.
ii. Suspension:
Suspension represents the floating of small sized particles in the air stream. Movement of such fine particles in suspension is usually started by the impact of particles in saltation. Once these fine particles are picked up by the particles in saltation and enter the turbulent air layers, they can be lifted upward in the air by eddy currents and they are often carried for several miles before being re-deposited elsewhere.
Dust particles will fall on the surface only when the wind subsides or the rain washes them down.
iii. Surface Creep:
Surface creep is the rolling or sliding of large soil particles along the ground surface. They are too heavy to be lifted by the wind and are moved primarily by the impact of the particles in saltation rather than by direct force of the wind. The coarse particles tend to move closer to the ground than the fine ones.
Threshold Velocity:
Threshold velocity is the minimum wind velocity required to initiate the movement of soil particles. The fluid threshold velocity is defined as the minimum velocity required initiating movement from the impact of soil particles carried in saltation. Threshold velocity varies with the soil conditions and nature of ground surface.
Some factors that influence the wind erosion are listed below:
(i) Characteristics of wind viz. speed, direction, structure, temperature, humidity and burden carried etc.
(ii) Characters of surface viz. roughness, vegetative cover obstructions and temperature.
(iii) Topography viz. flat, undulating and broken soil.
(iv) Nature and properties of soil viz., texture, structure, organic matter and moisture content.
In addition to these factors, soil cloudiness, surface roughness and crop residues are also the most important factors which contributed 75 per cent of the variability in the amount of wind erosion.
Soil Conditions:
Degree of cloudiness, mechanical stability of clods, presence or absence and stability of the surface crust, bulk and size of erodible soil fractions etc. also affect the wind erosion to a large extent. Consolidation of surface soil particles either as a crust or as clods holds them in large clusters to prevent erosion.
The cloddy soil was found to reduce the erosive capacity of the wind by decreasing the velocity of wind. Clods and ridges were found to act as soil traps and thereby decrease the severity of wind erosion.
Erodibility of soil can be related with the equivalent diameter of the particles. The equivalent diameter is equal to the product of bulk density and the diameter of soil particles divided by the particle density (2.65) of soil.
Equivalent diameter (de) =Bulk density × diameter of the soil particle/Particle density (2.65)
The most erodible soil particles are about 0.1 mm in equivalent diameter.
Surface Roughness:
Rough soil surface is more resistant to wind erosion than a smooth one. The degree of surface roughness depends on height and density of vegetative cover and on size, shape and lateral frequency of clods, ripples and ridges. Alternate ridges and furrow also provide for trapping of salting particles thus stopping the normal, build-up of eroding material down wind.
Crop Residues:
Living or dead vegetative matter greatly protects the soil surface from wind action. It not only reduces wind velocity at the soil surface, but also absorbs much of the force exerted by the wind. Vegetative materials trap drifting soil particles.
There are generally four basic methods that can control or reduce soil erosion caused by the wind.
(i) Protection of the soil surface with a vegetative cover or crop residues.
(ii) Bringing aggregates or clods to the surface soil because aggregates or clods are larger enough to resist the wind force.
(iii) By making surface roughness for the reduction of wind velocity.
(iv) Establishment of barriers or trap strips and wind breaks at suitable intervals at right angles to the most erosive winds to reduce wind velocity and soil drifting.
Essay # 4. Soil Erosion by Water:
In much the same way that wind erosion is caused by rapidly moving air, water erosion is caused by water moving rapidly across bare soil. As it flows down a slope, water tends to take into suspension first the finest material, the clay, and as it speeds up so it picks up progressively silt and then fine sand.
Three more or less distinct types of erosion are recognized, known as sheet, rill and gully erosion. In sheet erosion soil is removed fairly uniformly all ones the slope. In rill erosion numerous shallow gully’s or ‘rills’ are formed.
Clay imparts stability to soil, so soils containing more than about 35% clay are less susceptible to water erosion than soils low in clay, but the speed of water movement is the most important factor. This mainly depends on the steepness of the slope, but is also affected by the length of the slope.
Whether the water runs off rather than soaks into the soil depends to some extent on the steepness of the slope, but the intensity of the rain and the type of soil have even greater effects. The intensity of the rain and its duration determine the amount of water which the soil has to dispose of.
Water erosion of soil starts when raindrops strike bare soil peds and clods, resulting the finer particles to move with the flowing water as suspended sediments. The soil along with water moves downhill, scouring channels along the way. Each subsequent rain erodes further amounts of soil until erosion has transformed the area into barren soil.
Water erosion is due to the dispersive action, and transporting power of water—water as it descends in the rain and leaves the land in the form of run-off. Water erosion caused by people who remove protective plant covers by tillage operation, burning crop residues, overgrazing, over cutting forests etc. inducing loss of soil.
i. Raindrop Splash Erosion:
Rain drop splash erosion results from soil splash caused by the impact of falling rain drops.
There are four factors that determine the rate of rain drop erosion namely:
(i) Climate (mostly rainfall and temperature),
(ii) Soil—its inherent resistance to dispersion and its infiltration rate,
(iii) Topography particularly steepness and length of slope, and
(iv) Vegetative cover—either living or the residues of dead vegetation.
The continued impact of raindrops compacts the soil and further seals the surface—so that water cannot penetrate into the soil and as a result causing more surface run-off. The impact of rain drops per unit area is determined by the number and size of the drops, and the velocity of the drops.
ii. Sheet Erosion:
Sheet erosion is the removal of a fairly uniform layer of surface soil by the action of rainfall and run-off water. This type of erosion, though extremely harmful to the land, is usually so slow that the former is not conscious of its existence.
It is common on lands having a gentle or mild slope, and results in the uniform “skimming off of the cream” of the top soil with every hard rain. In this erosion, shallow soils suffer greater reduction in productivity than deep soils. Movement of soil by rain drop splash is the primary cause of sheet erosion.
iii. Rill Erosion:
Rill erosion is the removal of surface soil by running water, with the formation of narrow shallow channels that can be leveled or smoothed out completely by normal cultivation. Rill erosion is more apparent than sheet erosion.
Rills develop when there is concentration of run-off water and if neglected, they grow into large gullies. Rill erosion is more serious in soils having a loose shallow top soil. This type of soil erosion may be regarded as a transition stage between sheet and gully erosion.
iv. Gully Erosion:
Gully erosion is the removal of soil by running water, with the formation of channels that cannot be smoothed out completely by normal agricultural operation or cultivation. Gully erosion is an advanced stage of rill erosion.
Unattended rills get deepened and widened every year and begin to attain the form of gullies. During every rain, the rain water rushes down these gullies, increasing their width, depth and length. Gully erosion is more spectacular and therefore, more noticeable than any other erosion.
v. Stream Channel Erosion:
Stream channel erosion is the scouring of material from the water channel and the cutting of banks by flowing or running water. ‘This erosion occurs at the lower end of stream tributaries and to streams that have nearly continuous flow and relatively flat gradients.
Stream but erode either by run-off flowing over the side of the stream bank, or by scouring or undercutting. Scouring is influenced by the velocity and direction of flow, depth and width of the channel and soil texture.
The nature and properties of soils affect water erosion through influencing the rate of infiltration and dispersion of soils. Soil texture and structure also influences the soil erosion indirectly through the influence of infiltration and permeability. A compact surface is responsible for low infiltration and high run-off.
A coarse sandy soil has very high rate of infiltration of water and permits very little runoff. On the other hand, a fine textured clay and clay loam soils containing high amount of micr4opores which results low rate of infiltration and thereby accelerate soil erosion through surface run-off.
Water erosion causes various damages to the lands as follows:
i. Loss of Top Fertile Soil:
The surface soil lost as run-off consists of fertile soils and fresh or active organic matter. The eroded soil deposited in a river bed or reservoir is not only unavailable for agricultural use but is definitely harmful.
ii. Accumulation of Sand or Other Unproductive Coarse Soil Materials on Other Productive Lands:
In the plains, fertile lands have been made unproductive by the deposition or accumulation of soil material brought down from the hills by streams and rivers.
iii. Silting of Lakes and Reservoirs:
Soil erosion from the catchment areas of reservoirs results in the deposition of soil, thus reducing their storage capacity and minimising their useful life.
iv. Silting of Drainage and Water Channels:
Deposition of silt in drainage ditches in natural streams and rivers reduces their depth and capacity to handle run-off and at the same time the demand on these outlets is increased. As a result, overflows and flooding of downstream areas increase with damage to agricultural crops and also disaster to man-made structures.
v. Decreases Water Table:
With the increase in run-off, the amount of water available for entering the soil is decreased. This reduces the supply of water to replenish the ground water in wells, the yield of well is reduced.
vi. Fragmentation of Land:
Water erosion especially gully erosion may divide the land into several valleys and ridges and thus fields become smaller and more numerous. Crop rows are shortened, movement from field to field is obstructed and a result the value of land is decreased.
The major factors affecting water erosion are climate, topography, vegetation and soils. This can be written as,
Ew =f(c, t, v, s)
where,
Ww = Erosion due to action of water, c—climate, t—topography,
v—vegetation, and s—soils.
This equation comprises two types of variables—controllable and uncontrollable. Climate, the intensity of slope, and some physical characteristics of soils cannot be directly controlled. There effects, however, may be altered indirectly through the use of bunds and terraces which reduce the length of the slope.
i. Climate:
The major climatic factors influencing run-off and erosion are rainfall, temperature and wind, of which rainfall is the most important. Wind also influences the angle and impact of raindrops. The amount, intensity, frequency and duration of rainfall have a very definite effect on the amount and rate of the resultant run-off.
A large total rainfall may not cause much erosion if the intensity is low. Frequent rain maintains high moisture content of the soil and a low intake capacity and this increases run-off and erosion.
ii. Topography:
On flat or leveled lands, erosion is usually not a problem. The sloping lands experience increasingly greater problems of soil erosion. The intensity and length of slopes are the most important components of topography that affect soil erosion.
Velocity of the run-off water is influenced mainly by the intensity of slope. If the land slope is increased four times, the velocity of water flowing over it is approximately doubled and thereby erosive or cutting capacity is increased approximately by four times following the kinetic energy of the flowing water.
The length of slope is another factor which influences the soil erosion to a greater extent. Soil loss by erosion is proportional to the length of slope to the 0.5 power. Convex or dome-shaped slopes have more soil erosion as compared to concave or cup-shaped slopes.
iii. Vegetation:
A good vegetative cover like thick growth of grass or a dense forest may nullify the effects of climate, topography and soil on erosion. The important implications of vegetation on soil erosion are given below:
a. Interception of Rainfall:
A part of the rainfall intercepted by the canopy of vegetation never reaches the soil, but is evaporated directly from the leaves and stems. This part of the rainfall does not contribute to the run-off. Vegetative cover also minimises the dispersion of soil which in turn results less erosion.
b. Reducing Run-Off Velocities:
Well-distributed, close growing vegetation not only reduces the rate at which water travels down the slope, but also tends to prevent or concentration of water.
c. Root Effects:
The knitting and binding effect of root systems in the surface layer of soils, aggregate the soil into granules and increase its resistance to erosion.
d. Biological Influences:
The soil under a thick forest cover is permeated with channels of earthworms, beetles and other life. These channels increase the permeability of the soil. Vegetation, in addition, increases soil aeration which provides a better environment for the activity of beneficial bacteria.
e. Transpiration Effects:
Vegetation increases the storage capacity of the soil for rainfall, by the transpiration of large amounts of moisture from the soil.
Soil erosion caused by water is lessened by reducing either soil detachment or soil sediment transport or both.
i. Controlling Soil Detachment:
Soil detachment can be controlled by cropping or other vegetative cover practices that keep the soil covered as much as possible. As rain drops fall on the vegetation then the water gently slides off to be absorbed into the soil.
Stubble mulches help to control soil erosion through the prevention of direct fall of raindrops on the soil surface. The practice of using deep or subsurface tillage implements that leaves much of the crop-residues standing on the surface of the soil is stubble mulch farming, an effective technique of wind erosion control.
ii. Controlling Soil Sediment Transport:
Soil sediments transportation is hindered by slowing the eroding water, decreasing the steepness of slope, and by erecting barriers namely brushes dams, terraces, contour cultivation and contour strip cropping. Different kinds of terraces are shown in Fig. 27.1.
Terracing is generally recommended only for intensively used eroding crop land. Contour cultivation means tilling and planting at right angles to the natural slope of the land. i.e., on terraced fields, contour tillage should be parallel to the terraces.
Ridges formed during contour tillage are effective in reducing erosion. Contour tillage combined with terracing or contour strip cropping is more effective than contour alternate strips of intensively cultivated crops with strips of sod-forming crops.
Erosion sediments from the tilled strips are filtered out and retained on the sod like crop strips. The greater the proportion of sod-crop strips to cultivated strips, the less the erosion.
Essay # 5. Soil Erosion Due to Pollutions:
In recent decades, the use of inorganic fertilizers has increased dramatically at the expense of more traditional organic nutrient treatments. Between 1950 and 1985, the global use of fertilizers increased from the million tones to 125 million tones, an increase of almost 900%.
Inorganic fertilizers are used in preference to organic treatments because the nutrients are in a more readily available form and are released rapidly after application. Organic material releases its nutrients slowly, through decomposition processes, and only when conditions are suitable. Fertilizers are applied in a variety of forms – solution, suspension, emulsion and solid.
The solid forms vary in particle size from fine powders to coarse granules, and are spread evenly over the soil surface or mechanically placed, by drilling, into the rhizosphere; generally the rate of nutrient release decreases with increasing particle size.
Fertilizers are based on compounds of plant macro-nutrients, and micro-nutrients and a variety of nutrient combinations are available depending on the nature of the nutrient problem.
There are five main types of fertilizers applied to the soil – plant and animal uptake an exchange in the soil, leaching and loss in soluble form through drainage, volatilization and gaseous losses to the atmosphere and surface loss in solid form by run off and erosion. In terms of plant uptake, the percentage recovery of nutrients varies between the different types of fertilizers.
During the first year of application, the recovery of nitrogen from inorganic nitrogen fertilizers is about 50-65%, where as from organic manures it is only about 20- 30%. Similarly, the recovery of phosphorous and potassium from organic and inorganic fertilizers is about 5-15% and 75% respectively.
In terms of fixation in the soil, many of the phosphorous and potassium fertilizers are of relatively low solubility and the nutrients released are often strongly absorbed. In contrast many of the nitrogen fertilizers are highly soluble, nutrient release is rapid and in most soils absorption is limited.
The differences in degree of immobilization by plants and animals, and in the extent of fixation in the soil. This is why leaching losses of nitrogen are usually far greater than those of phosphorous and potassium.
Leaching is most common in coarse – textured and well drained soils, where as de-nitrification losses are the greatest in fine-textured, waterlogged and poorly aerated soils. Similarly, surface losses are greatest at sites which are most susceptible to surface run off and erosion.
In terms of the environmental problems associated with fertilizer use, perhaps the area which has received most attention is nitrate leaching. In the last few decades, levels of nitrates in water supplies have increased dramatically, particularly in intensively cultivated areas where inputs of nitrogen fertilizer have been high.
The main factors which, influence the extent of nitrate leaching include land use, soil characteristics and climate. In terms of land use, nitrate leaching tends to the greatest when there is no crop cover to utilize the nitrate released from fertilizers or organic reserves.
Tillage practices also have an effect on nitrogen losses through leaching and de-nitrification. Nitrate leaching is not restricted to arable land. Leaching occurs most frequently during the land preparation stages, prior to planting, where improved drainage and aeration lead to increased rates of organic mineralization, and after felling when the source of nitrogen uptake has been removed.
With respect to soil characteristics, coarse textured soils are particularly susceptible to leaching due to the often poor structure development and relatively large pore sizes. Under these conditions, surface run off may occur and leached nitrate is more likely to be transferred into surface waters than into ground waters.
Urban and industrial development has been associated with both physical degradation and chemical contamination of soils. Problems of physical degradation include erosion, compaction which involves the compression of a mass of soil into a smaller nature.
The case with which soils are compacted depends on a number of characteristics, particularly texture occurring most readily in soils which contain appreciable quantities of clay.
The compacting force, which usually acts in a vertical direction, causes alignment of the clay platelets in a direction which is more or less parallel to the ground surface alignment of the clay particles, in this way often leads to the formation of compaction or cultivation pans which may be a few centimetres in thickness.
Such pans tend to form at a depth of about 20-30 cm, are often characterized by a well developed platy structure, and are commonly associated with impeded drainage and restricted development of plant root networks.
If silty soils, raindrop impact may lead to surface crusting which is another form of soil compaction. Surface crusts may be several millimetres in thickness and are commonly associated with reduced infiltration, increased surface runoff and accelerated soil erosion.
Similarly, chemical problems result from waste disposal activities, discharge and spillage of liquid affluent and atmospheric emissions including acid deposition. Soils of urban and industrial environments are every bit as complex and variable in their characteristics as those in rural areas.
Physical disturbance and chemical contamination of soils in urban and industrial environments are not only recent phenomena. Archaeological investigation have revealed the extensive accumulation of building and domestic waste, although much of this was relatively harmless.
Since the Industrial Revolution of the eighteenth & nineteenth centuries, however the amount variety of waste materials have increased dramatically.
Essay # 6. Magnitude of Soil Erosion Problem:
While it takes nature 100 to 400 years to build one centimetre of top soil and man can often destroy it almost overnight by haphazard land use and improvement in husbandry. By erosion the soil is lost and its fertility deleted. It is reported that the annual loss of fertility by erosion is 20 times faster than what is removed by the crops. (Fig. 23.6).
It has been estimated that the loss of soil through erosion of arable land is of the order of 6,000 million tonnes a year, with a total annual depletion of nitrogen to the extent of nearly 2.5 million tonnes, valued at Rs. 1,000 crores of rupees.
According to an estimate “on an average area of 10,000 hectare is affected by erosion every year, involving an average loss of Rs. 500 lakhs.”
Investigations have shown that in the bare fallow fields in the foothills of northern India (except properly levelled rice land) a single storm leads to the loss of soil at the rate of 14 tonnes per acre; While in Bombay-Deccan there is a loss of 133 tonnes of soil per acre per year from a field of jowar.
Along most of the bigger rivers soil erosion has led to the formation of a vast and intricate network of fissures and finger gullies and the loss of invaluable agricultural land so that soil erosion is responsible for 3.67 million hectares of ravine lands in Uttar Pradesh, M.P., Rajasthan, and Gujarat along the banks of rivers flowing in north central direction viz., the Yamuna, the Chamal, the Mahi and the Sabarmati.
On a conservative estimate the country is losing a total output worth about Rs. 157 crores annually by failure to reclaim and develop the ravines.
Wind erosion is generally found in the desert areas of Punjab, Haryana, Western U.P., and western and north Rajasthan. In the desiccated area of Rajasthan the wind erosion has removed as much as 6 croresmaunds of soil per square mile in certain places during the last hundred years.
Wind borne sand encroaches arable lands of Rajasthan and makes them unfertile. Crops in many parts of western Rajasthan are frequently damaged by sand storms.
Essay # 7. Effects of Soil Erosion:
i. Loss of Soil:
The top soil is lost by erosion which is fertile soil. Due to formation of gullies and ravine valuable agricultural lands are lost.
ii. Effect of Erosion on Organic Matter and Soil Structure:
Erosion of upper layer of the soil decreases the content of organic matter. The structure of the soil becomes bad.
iii. Loss of Nutrient:
As the water continues to carry away the top soil, the nutrients of land declines. It is estimated that the annual loss of fertility by erosion is 20 times faster than what is removed by the crops.
iv. Effect of Soil Loss on Yield:
When soil is removed bodily from a field, both available and potential plant food along with mineral material is carried away. As erosion progresses, compact soil of relatively low infiltration capacity is approached. The ability of the land to supply moisture for plant growth is decreased, the beneficial activity of microorganism lessened. Due to these bad effects the yields are lowerd.
v. Hinderance of Farming Operations:
When a field is cut by rills and gullies, the difficulties of ploughing and other farm operations are considerably increased.
vi. Deposition of Sand and Gravel on Agricultural Lands:
Wind borne sand encroaches arable lands and makes them unfertile. Crops are damaged by sand storms. Water may also deposit sand and gravel on the agricultural lands.
vii. Heavy Floods in the River:
The destruction of the forest in the catchment areas of the rivers and their tributaries has caused rapid run-off and erosion leading to the deposit of an increasing mass of debris on river beds in lowlands thus increasing the damage from floods.
viii. Affect on Transportation:
Roads and railway lines are eroded by flood water thus creating hindrance in transportation.
ix. Destruction of Vegetation:
In wind erosion the large soil particles (or sand particles, have a cutting effect on tender plants). Dust laden winds burn up the- grasses. Destruction of vegetation by water is a frequent phenomena in flood prone areas.
Essay # 8. Conservation Measures for Preventing Soil Erosion:
The measures already adopted to prevent large scale soil erosion are:
i. Ploughing up of ravines.
ii. Levelling up of ravines.
iii. Contour ploughing.
iv. Contour building.
v. Strip cultivation.
Apart from these measures, emphasis was laid down to mass scale afforestation and orientation of agricultural fields at right angles to the prevailing wind direction, construction of granite walls, construction of terraces and dams throughout the country.