Factors affecting bacterial population in soil

Factors affecting bacterial population in soil

	Factors affecting bacterial population in soil Moisture It governs microbial activity in two ways-adequate supply is necessary (since water is the major constituent of protoplasm) but excessive moisture prevents microbial proliferation by limiting gaseous exchange and lowering oxygen supply thereby decreasing aerobic bacterial counts. Temperature Each bacterium has an optimum temperature for growth. Most are mesophiles preferring the range of 25-35°C. Certain species develop best at temperatures less than 20°C. They are called psychrophiles. Thermophiles are ubiquitous at temperatures from 45°C-55°C.
Organic matter Bacterial size is directly related to organic matter. Humus rich localities are richest in bacteria. Addition of carbonaceous materials and ploughing down of green manure or crop residues have a positive effect on the bacterial counts in soil. pH Highly acidic or alkaline conditions inhibit soil bacteria. Inorganic nutrients This commonly increase the bacterial numbers but ammonium fertilisers tend to suppress bacterial flora due to the acidity generated through the microbial oxidation of ammonium to nitric acid.
Cultivation practices Ploughing and tillage operations increase the number of soil bacteria by improving soil structure and porosity favouring aeration and altering the moisture status and exposing inaccessible organic nutrients to bacterial action. Seasons They playa minor role. In temperate regions, a burst of activity occurs in spring when soil becomes warm and rich in organic matter from the previous autumn. Thus the highest count of bacteria are seen in spring and autumn. Bacterial counts decline in hot summer and winter where cells remain in a state of biochemical inactivity.
Depth It is a secondary and variable factor. Bacteria are found more in the upper few centimetres. At the very surface, the bacterial community is less due to inadequate moisture and the bactericidal activity of the sun. The highest number is found at 1-2 cm from the surface and therefore the number declines with depth. Functions All major mineral transformations or biogeochemical cycling of nitrogen, carbon, sulphur, phosphorus, iron, manganese and other trace elements are due to the activities of the soil microflora. Mineralisation and immobilisation of minerals, production of growth hormones like gibberellins and auxins, and production of antibiotics and other commercially important products like enzymes are carried out by the soil microflora.

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