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Chapter: Microbiology

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Factors that influencing microbial population

Factors that influencing microbial population include 1) Soil mois-ture, 2) Aeration, 3) Temperature, 4) pH and 5) Organic and inor-ganic nutrient supply.

Factors that influencing microbial population

Factors that influencing microbial population include 1) Soil mois-ture, 2) Aeration, 3) Temperature, 4) pH and 5) Organic and inor-ganic nutrient supply. In addition to this, cultivation, ploughing, season and depth of soil also influence microbial population in soil.

Soil moisture :Soil moisture governs microbial activity in two ways.Since water is the major component of protoplasm, an adequate sup-ply must be available for vegetative growth and multiplication. But, where moisture becomes excessive, microbial proliferation is suppressed because the over supply of water limits gaseous exchange and lowers the available oxygen supply, creating an anaerobic environment. Moisture is present in the form of film in soil pores. The amount of water in-creases with increase in porosity of soil. Soil moisture is affected through irrigation, drainage or management practices.

Aeration : The air is essential for the growth of the aerobic organisms.The water logging condition brings about a decrease in the abundance of aerobic organisms. The change from an aerobic to a largely anaero-bic flora is effected by the disappearance of free oxygen as a result of its utilization by oxygen-requiring microorganisms, so that only micro-organisms tolerant of low oxygen levels complete anaerobiosis are ca-pable of proliferation.

Temperature :Temperature governs all biological processes and it isthus prime factor of concern to the microorganisms. Each microorgan-ism has an optimum temperature for growth. Most microorganisms are mesophilic that can able to grow between 25-35oC. Certain spe-cies develop best at temperature below 20oC and they are termed as psychrophiles. Thermophilic microorganisms that grow readily at tem-peratures of 45oC to 65oC.

pH :The neutral pH is favourable for many types of microorganisms.Highly acidic or alkaline conditions tend to inhibit many common mi-crobes. The greater hydrogen ion concentration, the smaller is the size of the microbial community. Soil-borne fungi are sensitive to high pH.

Organic and inorganic nutrients :These organic and inorganicnutrients are very important for microorganisms a s these provide nutrition for growth, activity and survival of microorganisms in soil. The chemical factors are gases, acids, micro and macro elements and clay minerals etc. In the soilsolution, gases and microorganisms are dissolved. However, the dissolved components are in constantly shifting equilibrium with the solid phase. The dead organic materials of plant and animal origin serve as total organic matter, which later is subjected to microbial colonization and decomposition. However, due to incorporation of green manures , crop residues etc., in soil, the community size of microorganisms gets increased. At the same time application of these organic matter alters the composition of soil microflora, microfauna and relative dominance of antagonistic micro-organisms. The types of vegetation and its growth stages of plant domi-nate one or more groups of soil microorganisms. Increased population of microorganisms can be found in the rhizosphere region according to season, growth stages and abundant availability of nutrients.


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