Soil Microbiology.pdf

Soil microbiology is a crucial component of agricultural soils, with the surface 6" of soil containing 3 ton/acre of soil organisms. These organisms, including bacteria, fungi, and protozoa, play essential roles in soil processes and functions. A teaspoon of soil can contain over a billion bacteria and yards of fungi mycelium. Soil microbes form complex and dynamic communities, with their relative dominance responding rapidly to changing conditions.

Bacteria are the most numerous and diverse group of soil microbes, with thousands of species, including actinomycetes and rhizobia. Fungi produce long strings of cells called hyphae, which form webs of mycelium, and are specialized to colonize roots and increase nutrient and water uptake. Protozoa and nematodes are larger and more complex than bacteria, feeding on other microbes and organic material.

Soil microbial biomass and activity tend to increase with increased soil organic matter (SOM). Management to increase SOM may be a feasible means to increase microbial activity. Factors affecting microbial biomass and activity include competition among soil microbes, soil temperature, water availability, pH, salinity, and the C:N ratio of organic materials.

Soil microbial activity approximately doubles with each 10°F increase in soil temperature, peaking at around 85°F. Microbial activity is very low at < 30 and > 110°F, but some species are adapted to extremes. Soil water availability favors microbial activity until excess water limits soil air movement. Microbes compete for energy, C, N, and other nutrients, and soil microbial activity increases with the addition of organic material to soil.

Soil microbial processes and functions include organic material decomposition, with much organic material added to the soil annually. The decomposition of around 11 t/ac/yr of organic material in the upper 4-6 inches of soil demonstrates the importance of soil microbes in agricultural ecosystems.