Soil Microbiological Properties

Microorganisms are the smallest living systems, but their activities are numerous. They represent the largest and most diverse biotic group in soil. Fertile soil usually contains 106–109 bacteria per gram of soil (Tugel and Lewandowski 1999). They play a vital role in soil texture by their organic secretions. Microorganisms are usually higher in the A horizon, and they contribute to the formation of the granular structure. Soil microorganisms consist of both prokaryotes and eukaryotes, including bacteria, protozoa, algae, fungi, and actinomycetes. However, in terms of bio-geo-chemical cycles, soil bacteria are very important. They are crucial in soil organic matter (SOM) decomposition, nutrient transformations, and small clay aggregation. Certain bacteria carry out unique roles in the soil. For instance, Rhizobia are nitrogen-fixing bacteria associated with legume roots, whereas protozoans (e.g., amoebas, ciliates, flagellates) are mobile microorganisms and live as heterotrophes by feeding on other soil microorganisms, and SOM algae are autotrophes like plants, photosynthesize, and are found near the soil surface. Another important soil microbial community is fungi, a diverse group of microorganisms. They are primarily responsible for the breakdown of SOM and have large aggregate stability. Structurally they have long hyphae or mycelia; these can spread yards to miles underneath the soil surface. These filaments help bind soil particles. Another considerably important soil microbial community is actinomycetes. These microorganisms have features of bacteria and fungi. They are prokaryotes like bacteria and have filamentous structures like fungi. They play a vital role in the degradation of SOM containing more resistant fractions. Also, actinomycetes are the principal agents in giving an earthy odor to soil. Nevertheless, bacteria dominate in agricultural and grassland soils, whereas fungi are more prevalent in forest and acidic soils (Tugel and Lewandowski 1999).