SOIL

SOIL :-

Plants are the means of life, for they are the sources of food for man and all other animals. The soil in which they grow is therefore an important factor in the production of all forms of life.

Soil is the loose material which forms the upper layer of the Mantle Rock (i.e. the layers of loose fragments which cover most of the earth's land area). It consists mainly of very small particles. It has no definite and constant composition. It contains both decayed plants and animal substances. There are four main types of substances in .varying proportion: Silica is present in soil in small crystalline grains which are the chief constituents of sand, Clay is a mixture of silicates and contains several minerals, comprising iron, potassium, calcium, sodium and aluminium. Particles of clay absorb water and swell, Chalk (calcium carbonate) provides the important element calcium, which is essential for the growth of plants, .Humus is not a mineral. It is an organic matter. It is formed by the decomposition of plant remains, animal manures and dead animals, and is the most important element in the fertility of soil. A soil looks dark on account of the presence of humus.

Soil may be said to consist of two layers i.e., the Top Soil ( the upper layer) and the Sub-soil (the parent material from which soil is formed). Below the sub-soil there is generally solid rock.

Process of Soil Formulation: Soil formation or pedogenesis depends first on weathering. It is this weathering mantle (depth of the weathered material) which is the basic input for soil to form. First, the weathered material or transported deposits are colonized by bacteria· and other inferior plant bodies like mosses and lichens. Also, several minor organisms may take shelter ·within the mantle and deposits. The dead remains of organisms and· plants help in humus accumulation. Minor grasses and ferns may grow: later, bushes and trees will start growing through seeds brought in by birds and wind. Plant roots penetrate down, burrowing animals bring up particles, mass of material becomes porous and sponge-like with a capacity to retain water and to permit the passage of air and finally a mature soil, a complex mixture of mineral and organic products forms.

SOIL EROSION :-

The proper use of soil resources has now become a matter of importance to all of us, because it directly affects our food supply. Due to various agents of soil erosion, man being a principal contributing factor, we are losing in a few years a resource which has required hundreds of years for development. In many parts of our country vast areas have been devastated by soil erosion.

The kind and degree of soil erosion depend much upon the texture and structure of the soil. It also depends on the soil erosion depend much upon the texture and structure of the soil. It also depends on the condition of climate and slope, nature of cultivation and other factors.

Causes of Soil Erosion: Running Water is the most important cause of destructive soil erosion. It takes place in two ways; (i) Gully Erosion and (ii) Sheet Erosion.

(i) Gully Erosion : Generally occurs on steep slopes when no vegetation is left to arrest the flow of storm water, which then finds its way downhill in a series of channels. Every fresh downpour widens and deepens the channels which develop into gullies. Gullies cut up agricultural land into small fragments and make them finally unfit for cultivation.

(ii) Sheet Erosion: The removal of an even layer from the whole top soil by water is known as Sheet Erosion. It is a steady gnawing process and may not be easily seen on the ground. The primary cause of sheet erosion is the cultivation of land on slopes. Cultivation weakens the soil. Rain water that previously was absorbed by the soil then runs off the surface, carrying soil with it. The action is even stronger when there are no trees and the plains are exposed to heavy storms. Generally, when a severe drought is followed by a sudden heavy storm of rain, sheet erosion takes place more quickly. This is because during the drought the surface soil becomes baked hard and the soil is unable to absorb water so easily. This increases the run-off. Sheet erosion is the more harmful because it i~moves the finer and more fertile of the soil particles first.

Wind: When the wind blows over land on which there is no vegetation cover, there will be damage to the top-soil. Wind erosion has caused grave destruction of soil in regions of scanty rainfall. Originally this semi-arid land had a sufficient cover of grass and bushes. which could hold the soil in place. Due to overgrazing or cultivation the natural balance is upset, and wind erosion occurs. The wind drives away· fine particles, which are the most fertile part of the soil.

Man is also responsible for soil erosion. His activities such as ploughing and the removal of natural vegetation help the wind, the running water and other agents. He is also responsible for allowing overgrazing of the land.