What is soil ? How does it form ?
What is soil ? How does it form ?
Soil is a mixture of small particles of rocks and humus (i.e., organic matter obtained from decaying of living organisms or their wastes). Temperature variations due to radiations of the sun, rain water, winds and living organisms influence the formation of soil from the rocks involving two processes: weathering and paedogenesis.
Breakdown of bigger rocks Into small, fine soil particles is called weathering. It may occur due to physical, chemical or biological means. Under the influence of solar radiations, rocks heat up and expand. At night, these rocks cool down and contract. Since all the parts of rocks do not expand and contract at the same rate, cracks appear in the rocks and ultimately the large rocks breakdown into smaller pieces. Flow of water through or over the rocks makes the cracks bigger. Flowing/falling water also has an erasing effect on the rocks. On freezing the water expands in rock crevices and breaks the rocks. Similarly, strong winds continue to rub against hard rocks and erode them. Growth of lichens, mosses and other plants also influence the formation of soil by eroding the rocks over which they are growing.
Paedogenesis: This process concludes the decomposition by bacteria and fungi, during which organic materials are broken down, leading to humification and mineralization. Detritivores such as nematods, earthworms, etc., consume organic matter and add excretory nitrogen to it. Thus, addition of organic matter (humus) from dead and decomposed plants and animals, is the final stage in soil formation.
Soil is a mixture of small particles of rocks and humus (i.e., organic matter obtained from decaying of living organisms or their wastes). Temperature variations due to radiations of the sun, rain water, winds and living organisms influence the formation of soil from the rocks involving two processes: weathering and paedogenesis.
Breakdown of bigger rocks Into small, fine soil particles is called weathering. It may occur due to physical, chemical or biological means. Under the influence of solar radiations, rocks heat up and expand. At night, these rocks cool down and contract. Since all the parts of rocks do not expand and contract at the same rate, cracks appear in the rocks and ultimately the large rocks breakdown into smaller pieces. Flow of water through or over the rocks makes the cracks bigger. Flowing/falling water also has an erasing effect on the rocks. On freezing the water expands in rock crevices and breaks the rocks. Similarly, strong winds continue to rub against hard rocks and erode them. Growth of lichens, mosses and other plants also influence the formation of soil by eroding the rocks over which they are growing.
Paedogenesis: This process concludes the decomposition by bacteria and fungi, during which organic materials are broken down, leading to humification and mineralization. Detritivores such as nematods, earthworms, etc., consume organic matter and add excretory nitrogen to it. Thus, addition of organic matter (humus) from dead and decomposed plants and animals, is the final stage in soil formation.
