Soil erosion and soil conservation: a detailed explanation

What is soil erosion ?

All the soils suitable and non-suitable for cultivation are destroyed by natural and artificial methods.

¹⁾The accumulation of the “top surface of the soil” by natural factors, mainly water and wind, by flowing or flying from one place to another is called soil erosion.

²⁾The physical movement of soil particles from one place to another is called soil erosion.

³⁾Soil erosion is a process of detachment and transportation of soil particles by erosive agents (wind and water).

Types of soil erosion

On the basis of the forces that promote soil erosion, there are two types of soil erosion-

1. Natural soil erosion– In covered soil, the erosion caused naturally by wind and water is called natural erosion.
2. Rapid or Human soil erosion or Artificial soil erosion– When the soil cover is removed by grazing by animals, digging or ploughing and the soil particles are carried away from the field by rain and wind by flowing and flying, it is called Rapid or Human soil erosion or Artificial erosion.
   
   “Rapid or Human soil erosion or Artificial erosion is called soil erosion in common colloquial language”.

Causes of soil erosion

There are following causes of soil erosion-

• Removal of soil cover- There is less erosion of soil covered by vegetation. But when these vegetation is cut and removed, then soil erosion starts by water and wind because the roots of the vegetation keep the soil tied.

• Cutting down of trees- Due to the cutting of forests, the soil becomes bare, due to which the speed of the flow of rainwater increases, which leads to soil erosion.

• Shifting cultivation- The practice of shifting cultivation was prevalent earlier in which people used to do farming by cutting down forests, which increased erosion, but now this practice is not in practice.

• Uncontrolled grazing in the meadows- When the grass cover is removed by the animals due to overgrazing, the soil erosion starts increasing.

• Faulty and unscientific farming systems- Soil erosion occurs more if ploughing, sowing, hoeing and weeding, harvesting etc. is not done according to the soil, place and situation and time is not taken into account.

• Farming on slopes- Cultivation on sloping lands leads to more erosion by water. For this it is best to do Contour or Terrace cultivation.

Factors Affecting Soil Erosion

There are mainly two factors affecting soil erosion-

1. Water erosion
2. Wind erosion

Water erosion

When raindrops fall on non-vegetated soil, they separate the soil particles from each other and scatter them, which move from one place to another with the flow of water, this is called water erosion.

Water erosion is of the following types-

• Drop or leap erosion- When raindrops fall from above, they cause the soil particles to bounce and throw them away, which is called Leap or Drop erosion.

• Sheet erosion- In sheet erosion, the top thin layer of soil gets washed away due to the strong flow of surface water.

• Rill erosion- When it rains, the water starts flowing in the form of small streams after layer erosion towards the slope of the field. The erosion of soil by these streams like thin tubes like fingers, is called Rill erosion. These very small tubes get erased after ploughing.

• Gully erosion- Due to the continuous and rapid flow of water on the slopes, the channels become more wide, then large cracks and small trenches are formed in the soil, it is called Gully erosion. Due to Gully erosion the soil is not remain cultivable and these areas are called ravines.

• Stream bank erosion- Where rivers and streams flow through, they keep cutting the soil on their banks. This damage becomes even more intense due to severe floods during the rainy season.

• Landslide erosion- When there is heavy rain on the mountains, the rocks become completely saturated with moisture and the loose rocks and plots on the steep slopes get eroded and roll down, this is called landslide erosion.

• Coastal erosion- The waves of sea water keep on eroding the soil of the banks. This type of erosion occurs in southern India mainly in Tamil Nadu and Kerala regions.

• Background erosion- Soils in which Leap erosion is more, some areas are visible at the time of erosion which are not affected by leap erosion because they are covered with plant roots and stones etc. These areas are called background and such erosion is Background erosion.

• Oceanic erosion- The area which is between the sea and the local vegetation area is called Beach. Soil erosion in this area occurs due to ocean waves as well as rivers which join the sea, it is also called Beach erosion.

Losses from water erosion

1. Obstacles in various agricultural activities.
2. The sub-soil opens up.
3. decrease in crop yield.
4. Due to the destruction of rain water, it is not useful in crop production.
5. The top surface of the soil and sometimes the sub-soil also gets washed away, which weakens the fertility of the soil.
6. Roads and railways get blocked.
7. When soil gets washed away with more water and collects on plain and fertile fields, the field becomes less fertile.
8. The soil, flowing along with water, accumulates at the bottom of rivers, streams, ponds and lakes, reducing their water holding capacity, which leads to floods in the border areas and also loss of public money.

Factors affecting water erosion

The factors affecting soil erosion by water are represented by the following equation-

E = F(C, T, S, V, H)

Where
E = Erosion
F = Factors
C = Climate
T = Topography
S = Soil Properties
V = Vegetation
H = Human Factors

The detailed description of the above factors is as follows:

• Climate- Soil erosion is more in case of prolonged and frequent high-speed rainfall. The greater size of the raindrops, the greater the dispersion of soil particles.

• Topography- Soil erosion is less on plain land than on sloping land. When the length and degree of slope is more, less time is available for the soil to absorb water, due to which soil erosion is more.

• Soil Properties- The scattering of sandy soil particles is high but the transfer is less. In loamy and clay or clayey soil, the particles stick together more strongly but the transfer of particles is more. Waste soil dissolves quickly in water and flows.

• Vegetation- Vegetation stops raindrops before they hit the soil particles. Therefore, the dispersion of soil particles does not take place and the rate of Run Off is reduced. Plants reduce erosion in many ways by increasing the amount of organic matter in the soil.

• Human Factors- Humans continue to cut forests for agriculture and other purposes, and due to excessive grazing in pastures, the soil becomes devoid of vegetation, apart from this, cultivating in the direction of slope on sloping soils and other faulty agricultural practices promote water erosion.

Wind erosion

Wind erosion generally occurs in areas without vegetation and high wind velocity. In wind erosion, soil particles are transferred from their original place to another place from the soil surface by flying with strong wind and strong storm etc.

“The erosion take place due o wind is called wind erosion”.

Activities involved in wind erosion

• Meandering- In India 5-25% of the area is affected by such activities. Particles of the size 0.5-1.5 mm are moved from one place to another by the gusts of wind by creeping on the soil surface, this is called Meandering.

• Upthrow- Most of the soil moves in a series of upthrow by the wind. Due to the direct pressure of the air, the particles of size 0.05-0.5 mm start to disperse from their place upwards and fall to another place and also scatter the particles where they fall. In this way the soil particles keep on moving.

• Suspension- Small soil particles (0.05-01 mm) are suspended in the atmosphere by the wind and are transferred for hundreds to thousands of kilometres.

Factors affecting Wind soil erosion

The factors affecting soil erosion caused by wind can be explained by the following equation.

E = F(C, T, V, S, W)

Where
E = Erosion
F = Factors
C = Climate
T = Topography
V = Vegetation
S = Soil Properties
W = wind speed

• Climate- Wind erosion is more in areas where climate is dry with less rainfall, higher temperature and faster westerly winds.

• Vegetation- Wind erosion is negligible in soils which are covered with vegetation with high altitude and bushy roots.

• Soil properties- Wind erosion is more in light soils with small particles, low density, lack of organic matter and rough surface.

• Topography- Wind erosion is more in sloping soils than in plain soils.

• Wind speed- wind erosion increases when the wind speed increases.

Process of soil erosion by wind

1. Initiation movement- Due to wind movement, the movement of soil particles starts, which is called Initiation, in which creeping action is prominent.
2. Transportation- The amount of transportation depends on wind speed, soil particle and weight, in which suspension and upthrow activities are prominent.
3. Deposition- The deposition of soil particles starts with the decrease in the holding power of the soil particles of air and the wind velocity.

Solutions to soil erosion

Methods of preventing soil erosion by water

Erosion adversely affects soil fertility and crop production. So it is very important to stop it. The methods of prevention of soil erosion by water are classified as follows-

1. Biological methods
2. Mechanical methods

Biological methods of Preventing Soil Erosion by water

Biological methods are further divided into the following subclasses

1. Agronomic activities
2. Tree planting

Agronomic activities

• Contour cultivation- All agricultural work and sowing of crops should be done parallel or opposite the slope along the line joining the places of equal height in the field. A contour is an imaginary line joining two points of equal elevation on the slope side.

• Planting Erosion Hinderance crops- Crops like Maize, Cotton, sunn hemp, Sorghum, etc., whose roots hold the soil firmly and have good vegetative cover, should be sown to prevent the soil erosion by water.

• Strip cultivation- Water and soil loss can be reduced by growing erosion resistant crops in parallel strips on the opposite side of the slope at almost contour locations. There are four methods of strip cultivation.
  1. Contour Strip cultivation
  2. Field Strip cultivation
  3. Wind Strip cultivation
  4. Permanent or Buffer Strip cultivation

• Crop rotation- Soil erosion can be reduced by adopting the crop rotation of “row-sown dense crops” and “non-row-sown and spreading legume crops”.

• Mulching– mulch is any material applied on the soil surface to check evaporation and improve soil water. It is defined as a natural or or artificially applied layer of plant residues or other materials on the surface of the soil. Mulches are used for various reason but water conservation and erosion control are the most important for agriculture in dry regions. e.g. crop residues, leaves manures, straw, plastic films etc.

• Use of manures- Dung manure, compost, green manure and cake manure etc. should be used. The use of manures improves the growth of vegetation, which prevents soil erosion.

• Methods of sowing- Sowing in rows is advantageous as compared to Broad casting method because the rows resist the flow of water.

• Irrigation- To prevent erosion, maximum area should be irrigated with minimum water. Irrigation by sprinkling method is very beneficial.

Tree planting

Forestry is the best means of preventing soil erosion. Forests do not allow rainwater to fall directly on the ground and prevent the rapid flow of water. Leaves of forest trees act as mulch and provide organic matter to the soil, which increases the water-holding capacity of the soil.

Land erosion can be stopped by planting trees like acacia, neem (Azadirachta indica), rosewood, plum, bamboo, jamun (Java plum), amla (Malacca tree), etc.

Mechanical methods of preventing soil erosion by water

Mechanical methods of soil conservation are adopted along with biological methods. Mechanical methods have the following principles.

1. To increase the time for water absorption and retention in the soil.
2. Reducing the speed of water flow by dividing a large slope into smaller slopes.

There are following mechanical methods of preventing soil erosion.

• Basin listing- Conservation of water is achieved by making interrupted basin along the contour lines by the Basin Lister tool, which reduces the flow of water. This method is adopted in soils having slope of 2%.

• Deep ploughing of subsoil- By breaking the hard and impermeable soil layer with the help of subsoiler, the water absorption and holding capacity of the soil increases. Due to which water conservation is good and soil erosion is less.

• Contour trenching- The soil is deposited in the form of bunds on the lower banks of the drain by digging 60 cm wide and 30 cm deep drains at appropriate intervals opposite to the slope and trees are planted over the drain.

• Contour terracing- Drains are prepared for drainage by bundling the soil on the contour lines, which conserves soil and water and stops the flow of water directly towards the slope.

• Bench terracing- Exhausts are made to drain out excess water safely. This method of soil conservation is highly successful in areas with high rainfall. Usually practiced in slope ranging from 16 to 33% on steep sloping and undulating land. The vertical drop Mein vary from 60 to 18 cm depending on the slope and soil conditions.

Methods of preventing soil erosion by wind

To prevent soil erosion caused by wind, it is necessary to pay attention to the following points-

• Reducing wind velocity on the soil surface.
• Increasing the size of the “soil particle cluster”.
• To keep the soil surface moist.

Keeping the above things in mind, soil erosion by wind can be controlled as follows:

1. Using green manure in crop rotation.
2. By growing perennial grasses in the soil.
3. By not leaving light soils fallow.
4. By not doing more tillage activities than necessary.
5. By strip farming.
6. By including leguminous crops and grasses in the crop rotation.
7. Leaving as much crop residue as possible in the soil at the time of harvesting.
8. By paying special attention to the main principles of dry farming.
9. By applying mulch in the field.
10. By planting wind-resistant trees in strips.
11. By planting very fine creeping and large number of root producing plants.

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