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Index >> Microbes and Lithosphere>>Soil Formation

Soil Formation

	Soil Formation Soil is the outer covering of the earth which consists of loosely arranged layers of materials composed of inorganic and organic constituents in different stages of organization. It is the natural medium in which plants live, multiply and die and thus provides a perennial source of organic matter which could be recycled for plant nutrition. It provides the physical support needed for the anchorage of the root system and also serves as the reservoir of air, water and nutrients which are so essential for the biotic flora of the soil. The process involved in the formation of soil are slow, gradual and continuous and are the sum total of environmental effects on rocks collectively known as the weathering of rocks.
Five important factors are involved in soil formation: (i) parent material, (ii) climate, (iii) topography, (iv) biological activity and (v) time. Growth in soil is very slow or nil for much of the time. Most of the microbial population must be dormant in the agricultural soils perhaps except in the rhizosphere and at sites of local litter input. Mean generation times for soil bacteria may be in the region of 5-10 days. Rock surfaces provide a suitable habitat for a limited number of organisms. Some bacteria, algae, fungi and more specifically lichens colonise the terrestrial rock surfaces.
Bacteria and fungi are found in crevices which can retain water. Along the shores of oceans large population of cyanobacteria and algae inhabit rocky coasts. Some examples include Calothrix, Chlorophycophyta members like Enteromorpha, Porphyra (Rhodophycophyta). Plant cover of the soil is an important factor in determining the types and number of microorganisms in that soil, since the plant root exudates and senescent parts of the plants are important sources of nutrients for soil microorganisms.
The extracellular polysaccharides that many microorganisms produce bind the individual soil particles together into crumbs. Hyphae of fungi and actinomycetes also playa part in this process. The crumb structure is very important in soil drainage and therefore in aeration. A soil with a good, well-developed crumb structure is freely draining and well aerated. Microbes generally live on particle surfaces or in the interconnecting spaces (pores) between the crumbs. The distribution of soil microorganisms vary according to various factors like soil temperature, soil water, soil air, soil pH and soil organic and inorganic nutrients.
	Bacteria in soil usually tend to grow as individuals or small microcolonies on the surface of the soil particles and roots. In contrast, fungi grow in the soil from a food base. Hyphae grow, come upon some utilisable organic matter, cover the surface by branching and as the substrate is exhausted, hyphae grow off again.

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