How Soil Bacteria Improve Soil's Fertility Status

Bacterial characteristics in soils

As with other soil organisms, the numbers of bacteria are extremely variable but high, ranging from a few billion to more than a trillion in each gram of soil. A biomass of a 400 to 5000 kg hectare liveweight is commonly found in the upper 15 cm of fertile soils.

Their ability to form extremely resistant resting stages that survive dispersal by winds, sediments, ocean currents and animal digestive tracts has allowed bacteria to spread to almost all soil environments. Their extremely rapid reproductive potential enables bacteria to increase their populations quickly in response to favorable changes in soil environment and food availability. As the early soil microbiologist Beijerinck expressed it, "everything is everywhere" when it comes to the bacteria. Change the soil environment, add a new substrate - even an industrial waste - and soon you'll find populations of bacteria feeding on it.

Soil Bacteria - Soil Science - Soil Management

Energy sources of soil bacteria

Most soil bacteria are heterotrophic - both their energy and their carbon come from organic matter. Heterotrophic bacteria, along with fungi and actinomycetes, account for the general breakdown of organic matter in soil. The bacteria often predominate on easily decomposed substrate, such as animal manures, starches etc. Where oxygen supplies are depleted, as in wetlands, nearly all decomposition, such as methane and nitrous oxide, have major effects on the global environment.

Importance of bacteria

Bacteria participate vigorously in virtually all of the organic transactions that characterize a healthy soil system. Because soil bacteria as a group possess such a broad range of enzymatic capabilities, scientists are now finding ways of harnessing, even improving, the metabolic activities of bacteria to help with the remediation of soils polluted by crude oil, pesticides, and various other organic toxins. Bacteria are usually the most important group in the breakdown of hydrocarbon compounds, such as gasoline and diesel fuel.

Importance of soil bacteria

In addition, bacteria hold near monopolies in several basic enzyme-mediated transformations. One such process is the oxidation or reduction of selected chemical elements in soils. Certain autotrophic bacteria obtain their energy from such inorganic oxidations, while anaerobic and facultative bacteria reduce a number of substances other than oxygen gas. Many of these biochemical oxidation and reduction reactions have significant implications for environmental quality as well as for plant nutrition. For example, through nitrogen oxidation, selected bacteria oxidize relatively stable ammonium nitrogen to the much more mobile nitrate form of nitrogen. Likewise, other bacteria are responsible for sulfur oxidation, which yields plant-available sulfate ions, but also potentially damaging sulfuric acid.

A second critical process in which bacteria are predominate is nitrogen fixation - the biochemical combining of atmospheric nitrogen with hydrogen to form organic nitrogen compounds usable by higher plants. The process can take place in soils independent of plants, but the amount of nitrogen fixed is much greater if the bacteria are intimately associated with plant roots, which can supply sugars to fuel the energy-intensive process.