Soil Bacteria

Bacteria are among the tiniest organisms living in soil. One gram of soil contains billions of bacteria. So far, more than 60,000 species of bacteria are discovered, and most of them are still unnamed. Each species of bacteria has its own particular features and characteristics. Most of them live in top 10 cm where the soil is covered with organic matter.

Main Characteristics of Soil Bacteria

  • Some species of bacteria are very delicate and can be easily destroyed by small changes in the environment of soil, but others are tough and they can live     in severe heat, cold or dry conditions.
  • Some bacteria species are inactive for decades because they do not have their favorable environment. They only become active when conditions are changed in their favor.
  • Many species of soil bacteria obtain nitrogen directly from air. Some of them break down toxic materials for obtaining nitrogen.
  • Population of bacteria can be multiplied in few days by making small changes in the environment of soil. For instance, you can change soil moisture, soil temperature or carbon substrate, and observe how these factors affect bacterial growth.
  • Some of the soil bacteria discharge special antibiotic substances to stop some particular challengers and as a result some species can inhibit other disease-causing microbes.


Important Types of Bacteria

  • Decomposers:  Organic materials can be easily decomposed by bacteria, especially in first step when moisture levels of the soil are high. In later steps of decomposition, fungi tend to dominate. Some examples of decomposer bacteria are Bacillus subtilisb and Pseudomonas fluorescens. Additions of decomposer bacteria have not been proved to increase the formation of compost or humus in soil.
  • Nitrogen fixers: To fix nitrogen in the soil, Rhizobium bacteria can be injected onto legume seeds. Specially nitrogen fixer bacteria live in root nodules on legumes like clover, lupine, medic, beans, wattles etc. These bacterias get nitrogen gas from fresh air and then they convert it into the special forms that plants can use, and this special form of nitrogen fixation is equal to above 100kg of nitrogen per hectare every year. Some of the free living nitrogen-fixing bacteria are Azotobacter, Azospirillum, Agrobacterium, Gluconobacter, Flavobacterium and Herbaspirillum. But increase in nitrogen fixation for non-legume crops is not possible.
  • Disease suppressors: A bacterium, Bacillus megaterium is used on some crops to reduce disease-causing fungus Rhizoctonia solani. Pseudomonas fluorescens could also be useful to reduce this disease. Bacillus subtilis is mostly used to stop fungus disease in sunflower plant’s seed which usually caused by Alternaria helianthi.  Today throughout the world a large number of bacteria are used commercially for disease suppression. Although the suppression cannot be used for all kinds of crops diseases, it is usually used in some particular crops.
  • Aerobes and anaerobes: The bacteria which need oxygen to live are called Aerobic bacteria, whereas, bacteria that do not need or need very little oxygen are Anaerobes. In well drained soil, aerobes tend to dominate, and anaerobes bacteria live inside soil aggregates. Anaerobic bacteria can limit plant root diseases by producing toxic compounds in poorly drained soils.
  • Actinobacteria: Actinobacteria live in non-acidic soils with higher ph level and that could be more then 5, and they slowly break down humates and humic acids in soils.
  • Sulfur oxidisers: Some bacteria such as Thiobacillus can break sulfides into a sulfur form called sulfate, which plants use easily.

How to Manage Bacteria:

Most of the species of bacteria are unhappy in dry conditions, acidity, salinity, soil compaction and in shortage of organic matter. Increase in population of bacteria could be a difficult task. When you add them in soil, it is not necessary that their population increase easily because they need favorable conditions. If the conditions are not favorable, the rate of multiplication of their population will be slow. You can manage bacteria population through:

  • First of all, focus on soil health problems, like acidity and compaction
  • Try to cover the whole ground with grass or mulch
  • Construct an ideal organic matter for bacteria. For instance, try to grow green      manure crops, mulching, strategic grazing and least tillage etc
  • Bad drainage system will encourage undesirable anaerobic bacteria

By taking care of these simple things, you can get great benefit and healthy populations of soil bacteria.  Soil bacteria’s population change very quickly depending upon moisture, time of year, type of crop, mulching, etc. If the ground is cover with organic matter, the population of soil bacteria increases rapidly.

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