|
We know more about bacteria than any other microoganisms common in soil. Bacteria are single-cell organisms, the simplest and smallest forms of life. They multiply by elongating and dividing into half and are therefore often called fission fungi. It is a simple process and under the right conditions, very rapid. A new organism may develop in twenty or thirty minutes easily. This gives them the unlimited capacity to increase in numbers and this is important in soils. It allows certain groups quickly to assume their normal functions under favorable conditions, even though their numbers were originally small. Bacteria can be considered as a force of tremendous magnitude in the soil.
In the soil, bacteria exists as mats, clumps, and filaments, called colonies, on and around the soil particles wherever food and other conditions are favorable. The jellylike mixture of mineral and organic colloidal matter makes an almost ideal medium for their development. Their existence depends on soil conditions, particularly food supply. Many of the soil bacteria are able to produce spores or similar resistant bodies, thus presenting both a vegetative and a resting stage. This is important as it allows the organisms to survive unfavorable conditions of many kinds.
There are many conditions in soil that affect the growth of bacteria such as temperature, moisture, aeration and food. The methods of determining the actual numbers present are quite inaccurate, since many organisms will not grow in the artificial media commonly used. It is almost impossible to break up the clumps or colonies in such a way as to determine the number of individuals actually present. It can be determined that the numbers of bacteria in soil are very large, possibly ranging as high as three or four billions to a gram of soil Good soils in general carry the largest numbers.
Soil bacteria is classified under two heads, autotrophic and heterotrophic. The autotrophic get their energy from the oxidation of mineral constituents, such as ammonium, sulfur,iron and most of their carbon from carbon dioxide. In numbers, they are insignificant, but since they include the organisms that support nitrification and sulfur oxidation, they are tremendously important in the sustenance of higher plants. Most soil bacteria, however, are heterotrophic, that is, their energy and carbon come directly from the soil organic matter. The general-purpose decay and ammonifying bacteria, as well as fungi and actinomyces, belong to this group.
Many conditions of the soil affect the growth of bacteria. Among the most important of these are the supply of oxygen and moisture, the soil temperature, the presence of organic matter, and the H-ion concentration of the soil solution.
All soil bacteria require for their growth a certain amount of oxygen. Some can continue their activities with much less free oxygen than can others. Bacteria require moisture for their growth, optimum water for higher plants seemingly being satisfactory for their best development.
Soil bacteria, like other plants, continue life and growth under a considerable range of temperature. The presence of a certain amount of organic matter is essential to the growth of most bacteria. Most bacterial thrive in a low acidity and low lime soil.
|
| |
