Authors: Seema, Neelam Yadav, Rekha Sodani, Jyoti Chauhan
Introduction : Microorganisms are a fundamental component of soils, playing a key role in essential processes such as organic matter dynamics, nutrient cycling, degradation of residues, and development of soil structure and aggregation. It enhances the overall health of plants. In the rhizoplane, ectorhizosphere and endorhizosphere, high populations of microbes dwell around plant roots which secrete biogenic substances. Soil-dwelling organisms protect the plant against pathogens. Bacteria and actinomycetes are important contributors to plant health – by forming symbiotic associations with roots, they supply the plant with nitrogen. Symbiotic fungi also exert a beneficial effect – they facilitate the supply of water and minerals, as well as protect the plant against pathogens and heavy metals (Jastrzębska, 2010). Also they have a relatively fast rate of turnover, and so they are commonly regarded as an early indicator of whatever changes have occurred in the soil environment (Sparling, 1997)."Fauna" comes from the Latin word of Faunus, the Roman goddess of earth and fertility, and the related forest spirits called Fauns. The term was first used by Linnaeus in the title of his 1745 work Fauna Suecica.
Direct and indirect chemical effects of soil macrofauna
- The most important chemical effect of macrofauna on soil is the modification of food quality through its passage in the gut and particularly mineralization of organic matter and the release of nutrients.
- Interactions between microorganisms (with a high capacity to digest almost all organic substrates) and macrofauna (with the potential for mechanical activities) are the basis of the biological systems of regulation that determine soil function
1. Cultural practices (Tillage)
- Cultural practices viz. cultivation, crop rotation, application of manures and fertilizers, liming and gypsum application, pesticide/fungicide and weedicide application have their effect on soil organism
- Ploughing and tillage operations facilitate aeration in soil and exposure of soil to sunshine and thereby increase the biological activity of organisms,
- Foliar or soil application of different chemicals (pesticides, fungicides, nematicides etc.) in agriculture are either degraded by the soil organisms or are liable to leave toxic residues in soil which are hazardous to cause profound reduction in the normal microbial activity in the soil.
2. Soil fertility:
- Fertility level of the soil has a great influence on the microbial population and their activity in soil.
- The availability of N, P and K required for plants as well as microbes in soil determines the fertility level of soil.
- On the other hand soil micro fauna has greater influence on the soil fertility level.
3. Soil moisture:
- Therefore optimum soil moisture (range 20 to 60 %) must be there for better population and activity of microbes in soil.
4. Soil temperature:
- Temperature is the most important environmental factor influencing the biological physical & chemical processes and of microbes, microbial activity and population in soil.
- Though microorganisms can tolerate extreme temperature (such as - 60 ° or + 60 u) conditions, but the optimum temperature range at which soil microorganisms can grow and function actively is rather narrow.
- In general, population and activities of soil microorganisms are the highest in spring and lowest in winter season.
5. Soil air (Aeration):
- For the growth of microorganisms better aeration (oxygen and sometimes CO2) in the soil is essential.
- Microbes consume oxygen from soil air and gives out carbon dioxide. Activities of soil microbes is often measured in terms of the amount of oxygen absorbed or amount of Co2 evolved by the organisms in the soil environment.
- Direct sunlight is highly injurious to most of the microorganisms .
- Effect of sunlight is due to heating and increase in temperature (More than 45°)
7. Soil Reaction / Soil PH:
- Soil reaction has a definite influence / effect on quantitative and qualitative composite on of soil microbes.
- Most of the soil protozoa prefer a neutral or slightly alkaline reaction between PH 4.5 and 8.0
8. Soil Organic Matter:
- The organic matter in soil being the chief source of energy and food for most of the soil organisms, it has great influence on the microbial population.
- Organic matter influence directly or indirectly on the population and activity of soil microorganisms.
- It influences the structure and texture of soil and thereby activity of the microorganisms.
9.Food and energy supply:
- Almost all microorganisms obtain their food and energy from the plant residues or organic matter / substances added to the soil. Energy is required for the metabolic activities of microorganisms.
- Thus, the source of food and energy rich material is essential for the microbial activity in soil. The organic matter, therefore serves both as a source of food nutrients as well as energy required by the soil organisms.
10. Nature of Soil:
- The physical, chemical and physico-chemical nature of soil and its nutrient status influence the microbial population both quantitatively and qualitatively.
- chemical nature of soil has considerable effect on microbial population in soil.
- The soils in good physical condition have better aeration and moisture content which is essential for optimum microbial activity.
11. Microbial associations / interactions:
Microorganisms interact with each other giving rise to antagonistic or symbiotic interactions. The association existing between one organism and another whether of symbiotic or antagonistic influences the population and activity of soil microbes to a great extent. The predatory habit of protozoa and some mycobacteria which feed on bacteria may suppress or eliminate certain bacteria.
12. Root Exudates :
- In the soil where plants are growing the root exudates also affects the distribution, density and activity of soil microorganism.
- Root exudates and sloughed off material of root surfaces provide an abundant source of energy and nutrients and thus directly or indirectly influence the quality as well as quantity of microorganisms in the rhizosphere region.
- Root exudates contain sugars, organic acids, amino acids, sterols, vitamins and other growth factors which have the profound effect on soil microbes
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About Author / Additional Info:
I am currently pursuing ph.D in Plant Physiology from Banaras Hindu University