Why are decomposing bacteria important to farmers

Of the mutualistic bacteria, there are four bacteria types that convert atmospheric nitrogen N 2 into nitrogen for plants. There are three types of soil bacteria that fix nitrogen without a plant host and live freely in the soil and these include Azotobacter, Azospirillum and Clostridium. The Rhizobium bacteria gram negative rod-shaped bacteria species associate with a plant host: legume alfalfa, soybeans or clover red, sweet, white, crimson to form nitrogen nodules to fix nitrogen for plant growth.

The plant supplies the carbon to the Rhizobium in the form of simple sugars. Rhizobium bacteria take nitrogen from the atmosphere and convert it to a form the plant can use. Figure 2 shows nitrogen fixing bacteria.

Many soil bacteria process nitrogen in organic substrates, but only nitrogen fixing bacteria can process the nitrogen in the atmosphere into a form fixed nitrogen that plants can use. Nitrogen fixation occurs because these specific bacteria produce the nitrogenase enzyme. Nitrogen fixing bacteria are generally widely available in most soil types both free living soil species and bacteria species dependent on a plant host.

Free living species generally only comprise a very small percentage of the total microbial population and are often bacteria strains with low nitrogen fixing ability Dick, W. Nitrite bacteria Nitrosomonas spp. Both nitrate and ammonia are plant available forms of nitrogen; however, most plants prefer ammonia because the nitrate has to be converted to ammonia in the plant cell in order to form amino acids.

Denitrifying bacteria allow nitrate NO 3 - to be converted to nitrous oxide N 2 O or dinitrogen N 2 atmospheric nitrogen. For denitrification to occur, a lack of oxygen or anaerobic conditions must occur to allow the bacteria to cleave off the oxygen. These conditions are common in ponded or saturated fields, compacted fields, or deep inside the microaggregates of soil where oxygen is limited. Denitrifying bacteria decrease the nitrogen fertility of soils by allowing the nitrogen to escape back into the atmosphere.

On a saturated clay soil, as much as 40 to 60 percent of the soil nitrogen may be lost by denitrification to the atmosphere Dick, W. Pathogenic bacteria cause diseases in plants and a good example are bacteria blights.

Healthy and diverse soil bacteria populations produce antibiotics that protect the plants from disease causing organisms and plant pathogens. Diverse bacteria populations compete for the same soil nutrients and water and tend to act as a check and balance system by reducing the disease-causing organism populations.

Streptomycetes actinomycetes produce more than 50 different antibiotics to protect plants from pathogenic bacteria Sylvia et al. Lithotrophs chemoautotrophs get their energy from compounds other than carbon like nitrogen or sulfur and include species important in nitrogen and sulfur recycling.

Under well-aerated conditions, sulfur-oxidizing bacteria make the sulfur more plant available while under saturated anaerobic, low oxygen soil conditions, sulfur reducing bacteria make sulfur less plant available. Actinomycetes have large filaments or hyphae and act similar to fungus in processing soil organic residues which are hard to decompose chitin, lignin, etc.

Actinomycetes decompose many substances but are more active at high soil pH levels Ingham, Actinomycetes are important in forming stable humus, which enhances soil structure, improves nutrient storage, and increases water retention.

Bacteria grow in many different microenvironments and specific niches in the soil. Bacteria populations expand rapidly and the bacteria are more competitive when easily digestible simple sugars are readily available around in the rhizosphere. Root exudates, dead plant debris, simple sugars, and complex polysaccharides are abundant is this region. About 10 to 30 percent of the soil microorganisms in the rhizosphere are actinomycetes, depending on environmental conditions Sylvia et al.

Many bacteria produce a layer of polysaccharides or glycoproteins that coats the surface of soil particles. These substances play an important role in cementing sand, silt and clay soil particles into stable microaggregates that improve soil structure.

Bacteria live around the edges of soil mineral particles, especially clay and associated organic residues. Bacteria are important in producing polysaccharides that cement sand, silt and clay particles together to form microaggregates and improve soil structure Hoorman, Bacteria do not move very far in the soil, so most movement is associated with water, growing roots or hitching a ride with other soil fauna like earthworms, ants, spiders, etc.

In general, most soil bacteria do better in neutral pH soils that are well oxygenated. Bacteria provide large quantities of nitrogen to plants and nitrogen is often lacking in the soil. Many bacteria secrete enzymes in the soil to makes phosphorus more soluble and plant available. In general, bacteria tend to dominate fungi in tilled or disrupted soils because the fungi prefer more acidic environments without soil disturbance.

Bacteria also dominate in flooded fields because most fungi do not survive without oxygen. Bacteria can survive in dry or flooded conditions due to their small size, high numbers, and their ability to live in small microsites within the soil where environmental conditions may be favorable.

Once the environmental conditions around these microsites become more favorable, the survivors quickly expand their populations Dick, W. Protozoa tend to be the biggest predators of bacteria in tilled soils Islam, In order for bacteria to survive in the soil, they must adapt to many microenvironments. In the soil, oxygen concentrations vary widely from one microsite to another.

Large pore spaces filled with air provide high levels of oxygen, which favors aerobic conditions, while a few millimeters away, smaller micropores may be anaerobic or lack oxygen. This diversity in soil microenvironments allows bacteria to thrive under various soil moisture and oxygen levels, because even after a flood saturated soil, lack of oxygen or soil tillage infusion of oxygen small microenvironments exist where different types of bacteria and microorganisms may live to repopulate the soil when environmental conditions improve.

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