Soil Formation

Soil is a result of several physical, chemical, and biological activities that go on constantly and the decay of various types of rocks. Biological activity is slowed or stopped if the soil becomes infertile or too dry. Organic matter increases in the soil when leaves fall and decay into it.

Process of Soil Formation 

• Weathering is the first process of soil formation (pedogenesis). The basic input for soil to form is the weathering mantle, i.e. (the weathered material depth)
• Bacteria and small creatures dwell in weathered material or transported deposits. It also serves as a home for lichens and mosses, which are inferior plant bodies
• The dead remains of plants and organisms help in humus accumulation
• Initially, grasses and ferns grow; later, bushes and trees start growing in these weathered areas through seeds brought in by birds and wind
• In the process of plant and tree root penetration, animals bring up particles by making burrows. The weathered material mass becomes porous and sponge-like, with a capacity to retain water and permit air passage. Finally, this leads to the formation of mature soil, i.e., a complex mixture of mineral and organic products

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Soil Forming Factors

• There are five basic factors that control the formation of soils: parent material, topography, climate, biological activity and time 
• These soil-forming factors act in union and affect the action of one another

Parent Material: 

• A passive control factor that controls soil formation is the Parent material
• These materials (Parent materials) can be on-site weathered rock debris or transported deposits or any in-situ weathered materials
• The formation of soil depends upon the structure, the texture of the debris size, and on the physical and chemical composition of the residual weathered rocks
• The rate of weathering, nature of debris and the depth of weathered deposits are important factors under parent materials.

Topography

• Another passive control factor is Topography

• The topography influence is witnessed from the amount of exposure of a surface covered by parent materials to sunlight and subsurface drainage over and through the parent materials

• Soil layer on steep slopes will be thin, and over flat upland areas will be thick

• The formation of soil is very favourable over gentle slopes where erosion is slow, and the percolation of water is nice

• Over flat areas, the formation of soil may develop a thick layer of clay with a good accumulation of organic matter, providing the soil with a dark colour.

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Climate

Climate is a very vital active factor in soil formation. The various factors that add to the formation of the soil development are:

• Temperature: Temperature effect in terms of both seasonal and diurnal variations.
  • Temperature action happens in two ways: firstly, in increasing or reducing chemicals and secondly, as biological activity. 
  • Chemical activity increases in higher temperatures and gets reduced in cooler temperatures (except for carbonation), and stops in freezing conditions. 
• Moisture: Moisture in terms of its intensity, frequency and duration of precipitation – evaporation and humidity.
  • Precipitation gives soil its moisture content that enables the biological and chemical activities in the soil. The downward transportation of soil components is helped by excess water through the soil (eluviation). It also deposits the same down below (illuviation). 

Biological Activity

• The organisms and the cover of vegetation that occupy the parent materials from the very beginning and also at several later stages with time help in the addition of organic matter, retention of moisture and gases like nitrogen, oxygen, etc
• Humus is the finely divided organic matter of the soil that is provided by Dead plants
• During humidification, few organic acids are formed that help in decomposing the minerals of the soil parent materials. The soil in and around warm and cold climates have differences in the intensity of bacterial activity.
• In cold climates, humus accumulation occurs as bacterial growth is slow. Low bacterial activity results in undecomposed organic matter, and therefore, layers of peat development happen in and around tundra and subarctic climates. Bacterial growth and action are high in humid, tropical, and equatorial climates, and dead vegetation is rapidly decomposed, leaving very low humus content in the soil. 

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Nitrogen Fixation

• • Nitrogen fixation is a process in which bacteria and other organisms present in the soil absorb nitrogen from the atmospheric air and then convert it into a chemical form that plants can use
  • Rhizobium is a category of bacteria that fixes gaseous nitrogen beneficial to the host plant. It resides in the root nodules of the leguminous plants. 

Time

The third important passive controlling factor in soil formation is time

• The time duration in the soil formation processes helps determine the maturation of soils and profile development
• Soil is said to be mature only when all soil-forming processes act for a considerably long time, therefore helping develop a nice soil profile
• Soils formed from the recently deposited glacial till or alluvium are considered young, and they exhibit only poorly developed horizons or no horizons.

Conclusion

Soil is the mixture of rock debris and organic materials which develop on the earth’s surface. The soil on which we depend so much for our day-to-day needs has evolved over thousands of years, and various agents of weathering and gradation have acted upon the parent rock material to produce a thin layer of soil.