Phases under which the Soil Development can be classified are as follows: (i) Weathering of parent rock (ii) Maturation and profile development.
(i) Weathering of parent rock:
The weathering is the process by which by large rocks are broken down to small pieces and converted to a fine powder. This is a long-term process occurring mostly under the influence the climatic condition of the area and hence called weathering. The weathering may be due to physical processes and/or chemical process and/or biological processes.
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The physical weathering takes place by the movement of rocks with running water and by the action of gravitational forces as landslide in mountainous regions. In deserts, large fluctuation in day temperature also causes breaking down of the rocks. The chemical weathering includes oxidation, hydrolysis and carbonation of minerals in the rock by weak acids like carbonic acid (H2CO3). The biological weathering includes the action various organisms particularly lichens and mosses which secret various organic acids and produce humic acids after death and decay.
(ii) Maturation:
The maturation process determines the structure of the soil profile and the type of the soil. It is largely influenced by climatic condition of the area.
There are four major maturation processes:
(a) Melanization:
In the region of low humidity, the humus derived from the dead organic matter gets mixed in the upper layer of the soil which becomes dark coloured.
(b) Podzolization:
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In the regions of high humidity high rainfall and low temperature, the minerals in the humus get leached from the upper horizon (eluvial) and get precipitated in middle of B- horizon forming a hard pan. This leaves an ash coloured surface layer of the soil from which the soil derives its name podzol.
(c) Qleization:
In very cold climates, the underground water lying above the rock layer continuously reacts with the partly weathered mineral matter. The hydrolysis and reduction of the minerals results in the formation of a hard gley horizon.
(d) Laterisation:
In very hot and humid climate, the rapid decay of organic matter and release of bases from organic combination results in the solubulisation of silica and formation of oxides of Fe, Al, Mn, etc. This results in a red coloured soil, rich ‘h iron and deficient in bases and organic matters.
A major consequence of ecosystem destruction and disturbance is degradation of land or soil which may be defined as the decline in soil quality through its misuse by human activity. In other words, the soil degradation means decline in soil productivity through adverse changes in nutrient status, organic matter, structural stability and concentration of toxic chemicals.
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The soil degradation includes soil erosion, compaction water excess and water deficit, acidification, salinisation and accumulation of toxic chemicals. Out of all the terms said above, the soil erosion is a most important degradation process having far reaching consequences.