Agricultural microbiology is a branch of microbiology dealing with plant-associated microbes and plant and animal diseases. It also deals with the microbiology of soil fertility, such as microbial degradation of organic matter and soil nutrient transformations.
Bacteria:- more dominant group of microorganisms in the soil and equal to one half of the microbial biomass in soil. Population 100,000 to several hundred millions for gram of soil - Autochthnous - Zymogenous groups. Majority are Heterotrophs. (Common soil bacteria - Arthrobacter, Bacillus, Clostridium, Micrococcus).
Actinomycetes - 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.
Fungi: More numerous in surface layers of well-aerated and cultivated soils-dominant in acid soils. Common genera in soil are Aspergillus, Mucor, Penicillium Trichoderma, Alternaria, Rhizopus. Algae – found in most of the soils in number ranges from 100 to 10,000 per g.
Protozoa: 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.
Importance of soil microorganisms
- Involved in nutrient transformation process
- Decomposition of resistant components of plant and animal tissue
- Role in microbial antagonism
- Participate in humus formation
- Predator to nematodes
- Surface blooming reduces erosion losses
- Improves soil structure
- Maintenance of biological equilibrium