Conservation of soil
Soil is the uppermost layer of the earth’s crust, which can be dug or ploughed. Land is a solid, substratum which supports human and many other...
Soil is the uppermost layer of the earth’s crust, which can be dug or ploughed. Land is a solid, substratum which supports human and many other organisms. A major percentage of the soil erosion is caused by human activities, but agents like air, wind and water erode the soil also contributing to imbalance in the ecosystems.
What is Soil Erosion?
Soil Erosion can be defined as the loosening and displacement of soil particles from the land. Soil erosion is a natural process. It may occur at a slow or fast rate. Soil degradation occurs through a slow and natural process (Geological process) or sometimes through a rapid process.
Geological erosion: It is a slow process which occurring for millions of years. The first phase of the soil forming process is called weathering. It leads to the breakdown of rocks by wind and water into small fragments and formation of soil particles. Fast process: Soil erosion accelerates when its vegetation cover is destroyed. This may occur due to natural causes like flooding or due to human activities.
One of the main human activities responsible for accelerated soil erosion is cultivation of land. Land under cultivation is more vulnerable to natural agencies like wind and water. The rate and extent of accelerated soil erosion is much higher compared to natural geological soil erosion.
Types of Soil Erosion:
Soil erosion can be classified by the physical agent responsible for erosion.
Running water erodes and carries soil particles with it. It is termed differently according to its intensity and nature of erosion- raindrop erosion, sheet erosion, rill erosion, steam banks erosion, erosion due to landslides, coastal erosion.
(i) Raindrop erosion: Raindrops displace soil particles and destroy soil structure. With continued rainfall, the displaced soil particles fill in empty spaces and prevent water from seeping into the soil.
ii) Sheet erosion: This kind of erosion takes place with flowing rain water and is a slow process.
(iii) Rill erosion: Finger like rills are formed on the land surface which slowly increase in number and width. When rills increase in size, they are called gullies. Ravines are deep gullies.
(iv) Stream bank erosion: The erosion of soil from banks (shores) of streams or rivers due to flowing water is called bank erosion.
(v) Landslide: Sudden mass movement of soil is called a landslide. Landslides occur due to instability or loss of balance of land mass with respect to gravity. Loss in balance occurrs mainly due to excessive water or moisture in earth’s mass. Gravity acts on such an unstable landmass and causes large chunks of surface material such as soil and rocks to slide down rapidly .
(vi)Coastal erosion: Coastal erosion of soil occurs along the sea shores. It is caused by the wave action of the sea and the inward movement of the sea into the land
When the soil is exposed to rain and heat, it loses its natural texture and is easily carried away by the wind. Such conditions occur mainly in arid and dry areas along the sandy shores of oceans, lakes and rivers. The loose soil particles are blown and transported with the wind thus:
(i) Siltation: Blown by wind in a series of short bounces.
(ii) Suspension: Transported over long distances in the form of suspended particles.
(iii) Surface creep: Transported at the ground level by high velocity winds.
Soil Erosion by human activities includes deforestation, farming, mining, economic and developmental activities.
Deforestation includes cutting and felling of trees and removal of forest litter. Browsing and trampling by livestock and forest fires also leads to deforestation. Deforestation leads to erosion and further to land degradation, nutrient and disruption of the delicate soil plant relationship.
Agriculture is a major human activity that causes soil erosion. Crops are grown, harvested and exposed to wind and rain. The above activities prevent replenishment of moisture. Agriculture also causes the gravest form of soil erosion on farmland in the form of wash-off or sheet erosion. In arid and semiarid areas, sand blows and sand shifts act in a similar to sheet erosion, where water is the chief agent. Following agricultural practices leads to soil erosion:
(i)Tilling or ploughing land increases chances of erosion as it disturbs the natural soil surface and protective vegetation.
(ii)Continuous cropping: Continuous cropping of the same land and extension of cultivation of marginal and sub-marginal lands encourages soil erosion.
(iii)Cultivation on mountain slopes: Cultivation on mountain slopes without appropriate land treatment measures such as bounding, terracing and trenching cause soil erosion and loss of soil nutrients.
(iv)Monoculture: Monoculture refers to the practice of planting the same variety of crop in the field.
Too many animals when allowed to feed on a piece of grassland repeatedly causes overgrazing. Trampling and grazing by cattle destroys the vegetation of the area. In the absence of adequate vegetative cover, land becomes highly susceptible to both wind and water erosion.
Soil erosion also occurs due to economic activities. The extraction of useful natural resources such as metals, minerals and fossil fuels from the land causes serious disturbance to land, leading to soil erosion and drastic changes in the landscape.
Soil erosion may also occur due to various developmental activities such as housing, transport, communication, recreation, etc. Building construction also promotes soil erosion because accelerated soil erosion takes place during construction of houses, roads, rail tracks etc. The construction of such facilities causes massive disturbance to land, resulting in soil erosion and disruption of natural drainage system.
Consequences of soil erosion:
- The fine particles of the topsoil containing the bulk of nutrients and organic matter required by plants are lost due to soil erosion. Erosion removes the most fertile part of the soil, leaving the less fertile subsoil behind.
- Erosion may result in removal of seeds or seedlings making the soil bare. Bare soil is more vulnerable to erosion both by wind and water