Organisms in the Soil:
Soil organisms spend all or part of their lives in soil environment. These organisms interact with the soil and soil conditions. This is by engineering the myriad of biochemical changes as decay occurs. They also physically churn the soil and help stabilize soil structure. These microflora and fauna incorporate plant and animal residues and waste products, creating soil humus, also recycling carbon and mineral nutrients, and supporting plant growth. Thus, there is need to lay stress on proper management of soils to encourage the healthy and diverse microflora and fauna community which will make nutrients readily available for plants and also protect environment.
Populations of soil organisms tend to be concentrated in zones of favorable conditions, rather than consistently distributed throughout the soil. As within the handful of soil, there may be areas of good and poor aeration, high and low acidity, moist and dry conditions, cool and warm temperatures, and localized concentrations of dissolved nutrients, organic substrates, and competing organisms. Thus, a high biological diversity of microbes is the indication of good soil quality.
Ecosystem Dynamics of Soil Organisms:
In most healthy soil ecosystems, there are many different species capable of carrying out of thousands of different enzymatic and physical processes which occur on daily basis. While the action of microflora is mostly chemical, that of the fauna is both physical and chemical. Activities of soil flora and fauna are so interrelated as to make it rather difficult to study them separately. So given the high degree of diversity, no single organism is probable to become entirely dominant.
Detritivores are soil organisms which depend primarily on detritus also known as debris of ecosystem. For soil organisms, their principal source of food is debris of dead tissues left by plants on soil and inside the soil pores. It is from this that organisms get their own energy.
Factors Affecting Growth of Soil Organisms:
Addition of any energy-rich organic substance comprising compounds excreted by plant roots stimulates microbial growth and activity. For instance, bacteria tend to respond rapidly to additions of simple compounds like starch and sugars.
Most microorganisms are aerobic, whereas some are anaerobic and use substances other than oxygen like nitrates and sulphate ions. In the meantime, facultative bacteria can utilize either aerobic or anaerobic forms of metabolism.
Moisture and Temperature:
Moisture and temperature differ from time to time in soil environment. Too high water content will limit oxygen supply; thus, optimum moisture level for higher plants is generally best for most aerobic microbes. Soil temperature extremes seldom kill bacteria but microbial activity is usually greatest when temperatures are 20 to 40o C.
Calcium and pH:
Levels of exchangeable calcium and pH aid find out which specific organisms thrive in the particular soil. High calcium and near-neutral pH usually result in the largest, most diverse bacterial populations.
Merits of Soil Organisms:
Organic Material Decomposition:
Soil detritivores are indispensable to plant productivity and ecological functioning of soils. This is accomplished by decomposition of dead leaves, roots and other plant tissues. The detritivores also incorporates wastes from animals.
Soil bacteria and fungi are particularly significant in helping maintain the nontoxic soil environment by breaking down toxic compounds like agrochemicals.
Transformation of Inorganic:
Nitrate, sulphate and phosphates ions are present in soils mainly due to the action of microorganisms. For example, bacteria and fungi incorporate some of the N, P, and S in organic materials they digest. Excess amount of these nutrients may be excreted in soil solution in inorganic form. In this manner, the soil food web converts organically bound forms of nitrogen, phosphorus and sulfur in mineral forms which can be taken up by higher plants.
Huge quantities of atmospheric nitrogen are fixed annually in forms usable by higher plants by actinomycetes in forest ecosystems, cyanobacteria in flooded rice paddies, wetlands and deserts, also rhizobia bacteria in agricultural soils.
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