The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time. Besides these, human activities also influence it to a large extent. 1. Parent Material Parent Material Parent material is a passive control factor in soil formation. Parent materials can be any insitu or on-site weathered rock debris (residual soils) or transported deposits (transported soils). Soil inherits many properties from the parent material from which it forms, for example, the mineral composition, the colour, the particle size and the chemical elements. For Example, The peninsular soils reflect the parent rock very much. The ancient crystalline and metamorphic rocks which are basically granite, gneiss and schist form red soils on weathering because they contain iron oxide. Soils derived from lava rocks are black coloured. Sandy soils are derived from sandstone. At the same time, the soils of the northern plains are transported and deposited from Himalayan and peninsular blocks, so they have little relation to rock material in-situ. 2. Climate Climate is an important active factor in soil formation. The role of climate is to vary the inputs of heat and moisture. It affects the rate of weathering of the parent rock. Hot and humid environments, in general, witness the most rapid weathering of parent materials. Role of precipitation: In areas that experience a lot of rainfall, water percolating down through soil tends to leach nutrients and organic matter out of the upper layers, unless modified by other soil components like plant roots. E.g. the soils underlying tropical rain forests tend to be nutrient-poor because of intensive leaching due to heavy rains; most of the nutrients are stored in the lush vegetation itself. Conversely, in arid regions with little annual precipitation, high rates of evaporation encourage the accumulation of salts in the soil. Role of temperature: Solar energy, usually expressed as temperature, controls the form of water falling onto the soil surface as well as in the soil. Also, it increases the rate of reactions, such as chemical reactions, evapotranspiration and biological processes. Wide fluctuations in temperature, especially in the presence of water cause shrinking and swelling, frost action and general weathering in soils. E.g. Laterite soils are found in alternate wet and dry climate. In Rajasthan, both granite and sandstone give birth to sandy soil irrespective of parent rock because of high temperature and wind erosion.
The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time. Besides these, human activities also influence it to a large extent. 1. Parent Material Parent Material Parent material is a passive control factor in soil formation. Parent materials can be any insitu or on-site weathered rock debris (residual soils) or transported deposits (transported soils). Soil inherits many properties from the parent material from which it forms, for example, the mineral composition, the colour, the particle size and the chemical elements. For Example, The peninsular soils reflect the parent rock very much. The ancient crystalline and metamorphic rocks which are basically granite, gneiss and schist form red soils on weathering because they contain iron oxide. Soils derived from lava rocks are black coloured. Sandy soils are derived from sandstone. At the same time, the soils of the northern plains are transported and deposited from Himalayan and peninsular blocks, so they have little relation to rock material in-situ. 2. Climate Climate is an important active factor in soil formation. The role of climate is to vary the inputs of heat and moisture. It affects the rate of weathering of the parent rock. Hot and humid environments, in general, witness the most rapid weathering of parent materials. Role of precipitation: In areas that experience a lot of rainfall, water percolating down through soil tends to leach nutrients and organic matter out of the upper layers, unless modified by other soil components like plant roots. E.g. the soils underlying tropical rain forests tend to be nutrient-poor because of intensive leaching due to heavy rains; most of the nutrients are stored in the lush vegetation itself. Conversely, in arid regions with little annual precipitation, high rates of evaporation encourage the accumulation of salts in the soil. Role of temperature: Solar energy, usually expressed as temperature, controls the form of water falling onto the soil surface as well as in the soil. Also, it increases the rate of reactions, such as chemical reactions, evapotranspiration and biological processes. Wide fluctuations in temperature, especially in the presence of water cause shrinking and swelling, frost action and general weathering in soils. E.g. Laterite soils are found in alternate wet and dry climate. In Rajasthan, both granite and sandstone give birth to sandy soil irrespective of parent rock because of high temperature and wind erosion.
Geo-Final-Key.docx