Soil Microbiology: Microbial Groups in Soil
- The field of soil microbiology was explored during the very last part of 19th century.
- The establishment of the principal roles that microorganisms play in the biologically important cycles of matter on earth: the cycles of nitrogen, sulphur and carbon was largely the work of two men, S. Winogradsky (1856-1953) and M.W. Beijerinck (1851–1931). S. Winogradsky, Russian and regarded by many as the founder of soil microbiology, discovered nitryfiying bacteria (1890-91); described the microbial oxidation of H2S and sulphur (1887); developed the contributed to the studies of reduction of nitrate and symbiotic nitrogen fixation; and, originated the nutritional classification of soil microorganisms into autochtonous (humus utilizers) and zymogenous (opportunistic) groups.
- Almost equally important was the work of M.W. Beijerinck, a Hollander, who isolated the agents of symbiotic (1888) and non-symbiotic aerobic (1901) nitrogen fixation.
- However, the greatest contribution of Beijerinck was a new and profoundly important technique: enrichment culture technique: to isolate and study various physiological types of various microorganisms from natural samples through the use of specific culture media and incubation conditions.
- Bacteria more dominant group of microorganisms in the soil and equal to one half of the microbial biomass in soil.
- Majority are Heterotrophs. (Common soil bacteria -Arthrobacter, Bacillus, Clostridium, Micrococcus).
- intermediate group between bacteria and fungi.
- Numerous and widely distributed in soil.
- Abundance is next to bacteria. 104-108/g soil.
- 70% of soil actinomycetes are Streptomyces.
- Many of them are known to produce antibiotics. Population increases with depth of soil.
- More numerous in surface layers of well-aerated and cultivated soilsdominantin acid soils.
- Common genera in soil are Aspergillus, Mucor, Penicillium Trichoderma, Alternaria, Rhizopus.
- Found in most of the soils in number ranges from 100 to 10,000 per g.
- Unicellular –population ranges from 10,000 to 100,000 per g of soil.
- Most of the soil forms are flagellates, amoebae or ciliates.
- Derive their nutrition by devouring soil bacteria.
- Abundant in upper larger of the soil.
- They are regulating the biological equilibrium in soil.
• Involved in nutrient transformation process
• Decomposition of resistant components of plant and animal tissue
• Role in microbial antagonism
• Participate in humus formation
• Predator of nematodes
• Surface blooming reduces erosion losses
• Improve soil structure
• Involved soil structure
• Maintenance of biological equilibrium