The Importance Of Microorganisms In Soil

Since the golden age of microbiology, there has been emphasis on the microorganisms that could be potentially pathogenic to both plants and animals (Cullimore, 2000). This has led to concentration on pathogenic microorganisms rather than environmentally important microbes. The environmental processes were then labelled as a series of natural chemical reactions that were abiotic (Lynch, 1998). The word biotic can be interpreted as an absence of life (i.e sterile), which is untrue about soil (Cullimore, 2000).

According to David (1998), soil is defined as the biologically active, porous medium that has developed in the uppermost layer of the Earth’s crust. Soil is one of the principal substrates of life on earth, serving as a reservoir of water

It is believed that between two and four billion years ago, the first ancient and microorganisms came about in Earth's primitive seas. These bacteria could fix nitrogen, in time multiplied and as a result released oxygen into the atmosphere (Willey, 2011).

This release of oxygen led to more advanced microorganisms (Lynch, 1983). Microorganisms in soil are important because they affect the structure and fertility of different soils. Soil microorganisms can be classified as bacteria, actinomycetes, fungi, algae, and protozoa. Each of these groups has different characteristics that define the organisms and different functions in the soil it lives in (Subba, 1999).

Microorganisms are generally divided into five major taxonomic categories algae, fungi, bacteria, protist and viruses (Willey, 2011). In the soil they are closely associated with the soil particles; mainly clay and organic matter complexes. microbes in the soli can be found as single cell or as biofilms embed in a matrix of polysaccharides, their activity and interaction with other microbes, organisms and with soil particles depend on the conditions at microhabitat level, which may even differ over a very small distance, soil can therefore be regarded as being highly heterogeneous with respect to a distribution of soil matter and organisms (Morse

Soils contain about 8 to 15 tons of bacteria, fungi, protozoa, nematodes, earthworms, and arthropods. Bacteria play an important role in decomposition of organic materials, especially in the early stages of decomposition when moisture levels are high (Cullimore, 2000).

In the later stages of decomposition, fungi tend to dominate because most are mainly saprophytes (decomposers) (Roberts, 2011). Bacillus subtilis and Pseudomonas fluorescens are examples of decomposing bacteria. Additions of these bacteria have not been proved to accelerate formation of compost or humus in soil (Lynch, et al 1998).

Organic matter decomposition serves two functions for the microorganisms, providing energy for growth and supplying carbon for the formation of new cells (Roberts, 2011). Soil organic matter is composed of the “living” (microorganisms), the “dead” (fresh residues), and the “very dead” (humus) fractions. The “very dead” or humus is the long-term soil organic matter fraction that is thousands of years old and is resistant to decomposition (Willey,