SOIL CONSERVATION

KRISHNA POUDEL

SENIOR AGRICULTURE INSTRUCTOR

DEPARTMENT OF PLANT SCIENCE

SHREE TRIVENI SECONDARY SCHOOL

PROVINCE 1, NEPAL

CONTACT: +9779847016830

KRISHNA POUDEL (RESEARCHGATE.NET)�E-MAIL: POUDELKRISHNA994@GMAIL.COM

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INTRODUCTION TO SOIL CONSERVATION

• Soil conservation is the combination of the appropriate land use and management practices that promote the productivity and sustainable use of soil and in the process minimize the soil erosion and other four of land degradation.
• Soil and water conservation is necessary for sustained productivity of land.
• Soil erosion is prevented or reduced to a tolerable level, and water is conserved for judicious utilization.
• Sustainable production implies that agricultural practices would lead to economic gains without impairing environmental quality and the usefulness of the soil for future generation.

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Objectives for soil and water conservation are:

• Promotion of proper land use
• Prevention of soil erosion
• Restoration of the productivity of eroded land
• Maintenance of soil productivity
• Control of runoff, and regulation of water resource through irrigation and drainage
• Maintenance of environmental quality by preventing land and water pollution.

EROSION

• Erosion is a process of detaching soil particles from the land surface of one place and their transportation and deposition to another place.
• Three processes of erosion:

1. Detachment :

This is the process when the soil particles detach from the surface. It depends upon type of soil, OM, moisture, nature of detaching agents (energy).

2. Transportation:

The detached particle gets transported into the destination place. This process depends upon size, density and shape of detached materials and velocity of the transporting agent.

3. Deposition:

Soil that is eroded from the original location is always deposited somewhere else. This may be close to its place of origin position; it may be the longest distance down to the sea or at any point between the places of origin to the sea. Process depends upon soil particles and velocity of the agent.

Causes of soil erosion

1. Rainfall and Flooding

Higher intensity of rainstorm is the main cause of soil erosion. Four types of soil erosion are caused by rainfall:

Rill erosion

Gully erosion

Sheet erosion

Splash erosion

The raindrops disperse the soil, which is then washed away into the nearby streams and rivers. Regions with very heavy and frequent rainfall face a large amount of soil loss. The flowing water during floods also erodes a lot of soil by creating potholes, rock-cut basins, etc.

2. Agriculture

The farming practices are the major cause of soil erosion. The agricultural activities disturb the ground. The trees are cleared and the land is ploughed to sow new seeds. Since most of the crops are grown during the spring season, the land lies fallow during winters. Most of the soil is eroded during winter. Also, the tyres of tractors make grooves on the land, making a natural pathway for water. Fine soil particles are eroded by wind.

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3. Grazing

The grazing animals feed on the grasses and remove the vegetation from the land. Their hooves churn up the soil. They also pull out plants by their roots. This loosens the soil and makes it more prone to erosion.

4. Logging and Mining

A large number of trees are cut down to carry out the logging process. Trees hold the soil firmly. The canopy of the trees protects the soil from heavy rainfall. The leaf litter that protects the soil from erosion, is also lost during logging.

Mining activities also disturb the land and leave the soil more prone to erosion.

5. Construction

The construction of roads and buildings exposes the soil to erosion. The forests and grasslands are cleared for construction purposes, which exposes the soil making it vulnerable to erosion.

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6. Rivers and Streams

The flowing rivers and streams carry away the soil particles leading to a V-shaped erosion activity.

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7. Heavy Winds

During dry weather or in the semi-arid regions, the minute soil particles are carried away by the wind to faraway lands. This degrades the soil and results in desertification.

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TYPES OF SOIL EROSION

1. Air/Wind erosion:

Wind erosion is the process of detachment, transportation and deposition of soil materials by wind.

The basic causes are: -

• Loose, dry and finely divided soils
• Smooth and bare soil surface
• Strong wind
• Large field

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TYPES OF SOIL MOVEMENT IN WIND EROSION

• Suspension, saltation, and surface creep are the three types of soil movement which occur during wind erosion.
• While soil can be blown away at virtually any height, the majority (over 93%) of soil movement takes place at or below one meter.

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Suspension :

• Soil particles and aggregates less than 0.1 mm in diameter (silt size and smaller ) are suspended by air currents, after being dislodged by saltating particles that can be air.
• Suspension occurs when very fine dirt and dust particles are lifted into the wind.
• They can be thrown into the air through impact with other particles or by the wind itself.
• Once in the atmosphere, these particles can be carried very high and be transported over extremely long distances.
• Soil moved by suspension is the most spectacular and easiest to recognize of the three forms of movement.

Saltation

• This is the process in which fine particles (0.1 to 0.5 mm in diameter) are lifted from the soil surface by wind turbulence and follow distinct trajectories under the influence of wind forces, air resistance, and gravity.
• In other words, the particles move in a series of short leaps.
• The jumping grains gain a great deal of energy, and may knock other grains into the air or bounce back themselves.
• The particles remain close to the ground as they bounce.
• The particles are often stopped by obstructions or reduced wind velocity.

Surface creep

• This is the rolling and sliding along the surface of the larger particles.
• Soil grains larger than 0.5 mm cannot be lifted.
• This causes them to roll and slide along the surface after coming into contact with saltating particles.
• The soil aggregates or gravel which cannot be eroded are left in place to provide a cover called desert pavement or lag gravel.

Factors affecting wind erosion

Soil moisture

• Wet soil does not blow because of the adhesion between water and soil particles.
• Dry winds generally lower soil moisture to below wilting point before wind erosion takes place.

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Wind velocity :

• The rate of wind movement, especially gusts having greater than average velocity will influence wind erosion.
• Standard wind velocity is measured at a fixed height of 9 m above the ground.

Height:

• Velocity of even a steady wind increases dramatically above the ground surface.
• Wind velocity over a bare surface is zero at a height close to the surface below the tops of irregularities.

Wind turbulence

• Wind strong enough to cause erosion is always turbulent
• Turbulence increases with increases in friction velocity, with increasing surface roughness, and with pronounced changes in surface temperature.
• It is more pronounced near the soil surface than higher in the wind stream.
• Turbulence is important in keeping soil grains suspended in air.

Surface roughness:

• Wind velocity is less severe when the surface is rough. This can be achieved by tillage, ridging and/or mulching

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Soil properties

• Some soil properties which influence wind erosion are

(i) stability of soil aggregates

(ii) size of erodible soil fractions: The presence of clay, organic matter and other cementing agents enhance aggregate stability

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Vegetation:

• Vegetation or residue mulch especially those with rows running perpendicular to the prevailing wind direction reduce winds erosion.
• Wind velocity approaches zero near the soil surface in a vegetated area.
• In addition, plant roots bind the soil.

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Length of exposed area :

• Soil drifting increases substantially with increasing length of the eroding strip.

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Water erosion :

Soil erosion by water can be primarily linked to rainfall, although water in motion erodes soil, rivers scour soil away, and waves erode shores.

Therefore, soil erosion can be defined as the detachment and movement of soil particles by the erosive forces of water.

Soil detached and transported away from one location is often deposited at some other place.

TYPES OF WATER EROSION

1. Rain Drop or Splash Erosion

The erosion due to the impact of falling raindrops on soil surface leading to the destruction of the crumb structure is known as the raindrop or splash erosion.

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2. Sheet Erosion

It is the uniform removal of soil in thin layers from the land surface caused by the wind. Land areas with loose, shallow topsoil overlie compact soil are most prone to sheet erosion

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3. Rill Erosion

Rill erosion is a form of water erosion in which the erosion takes places through numerous narrow and more or not so straight channels called streamlets, or head cuts. Rill is the most common form of erosion, which you can also observe during heavy rain.

4. Gully Erosion

Gully erosion occurs due to the runoff of surface water causing the removal of soil with drainage lines. Gullies when started once, will move by headward erosion or even by slumping of side walls unless and un-till proper steps will be taken in order to stabilize the disturbance.

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5. Stream Bank Erosion

Bank erosion is nothing but washing up away from banks of a stream or a river. It is different from the erosion of the bed of a watercourse, that is referred to as scouring