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Beneficial Bacteria in Garden Soil

Legume Bacteria That Fixate Nitrogen
Non-legume Bacteria That Fixate Nitrogen
Other Beneficial Bacteria


Legume Bacteria that Fixate Nitrogen:

Legumes can form symbiotic relationships with rhizobium bacteria. The rhizobia fixate nitrogen in exchange for carbohydrates from the plant. But many crops will benefit because most beneficial rhizobium will also suppress harmful bacteria. For maximum nitrogen fixation, legumes must be terminated after blooming begins but before seeds begin to form. Seed formation will use up the nitrogen.

Each legume has one or two primary rhizobium bacteria that will maximize nitrogen fixation. Sometimes there are also several secondary bacteria that will fixate nitrogen to a lesser degree. Sometimes these bacteria commonly exist in soil, but sometimes they do not and the seed must be inoculated before it is planted.

University of Kentucky - Rhizobia Inoculation of Legumes
Iowa State - inoculants by legume type
University of Hawaii - cross inoculation

Some legumes will fix more nitrogen than others. Listed here are links which rank legumes by level of fixation.

Nitrogen fixers ranked
USDA Farmers Bulletin 2003 - Legume Inoculation
FAO - nitrogen fixation rankings
Australian Society of Agronomy - fenugreek rhizobia nitrogen fixation

Under reasonable conditions, some rhizobia inoculations survive at useful levels for about 3-5 years without the proper leguminous host plants. Rhizobia will survive longer if given good conditions. Good conditions are high humus, PH around 7, moderate moisture, and moderate temperature. To help preserve bacteria, disturb the soil as little as possible and keep it mulched to prevent summer heat extremes.

Soil inoculation works best; PH and moisture
Survival of Rhizobia Without a Host
Rhizobial longevity
Research Review

In order to determine the bacterial status of your soil, plant some legumes inoculated with the maximizing rhizobium for each legume type. Adjust all other factors until you get good nodulation. The presence of pink nodules is proof that nitrogen is being fixed. Use those results as a baseline to measure all future judgements against. Then plant some legumes without inoculation. If the un-inoculated legumes have just as much good nodulation as the inoculated legumes, then you do not need to inoculate. The same test can be done in future years to determine whether it is necessary to re-inoculate. Miscellaneous links on the subject are listed below.

Nodulation examples
eOrganic - rhizobia
Legume Inoculant Production in Australia
Manufacture of Inoculants in New Zealand
Microbial Inoculant - Wikipedia

Non Legume Bacteria that Fixate Nitrogen:

Endophyte bacteria can increase atmospheric nitrogen fixation ( even in non-legume species ), produce growth hormones, increase the effectiveness of mycorrhizal fungus, and naturally suppress disease. The cheapest and easiest way to encourage endophytes is with organic practices including no-till, cover crop cocktails mulched in place, diverse crop rotations, and including animals into row crop rotations. Endophytes are everywhere and they are very ecologically sensitive so you do not need to purchase them or ferment for them. Let nature do the work for you.

Research Gate - bacterial endophytes

Most of these non-legume bacteria are naturally occurring and are encouraged by grass roots. Research to date has been inconsistant. Instead of buying these inoculums, a better approach may be to simply include grass family members in your vegetable rotation.

ASM - inoculation has no effect or is inconsistant

Azospirillum sp. is an endophyte which mineralizes nutrients and favors beneficial mycorrhizal plant associations. Mainly used with the grass family and trees, but some recent research of use on vegetables has been favorable.

Paenibacillus sp. - anaerobic, endospore-forming bacteria. Mainly used with the grass family but some recent research of use on vegetables has been favorable.

Klebsiella - a free-living diazotroph. Mainly used with the grass family.

Azotobacter - aerobic bacteria propagates free of living plants. Encouraged by grass. This is one reason mulch is so important; it provides organic matter for the bacteria to feed on.

Pseudomonas - free living bacteria capable of both aerobic and anaerobic metabolism in rice.

Azotobacter fixes nitrogen from the atmosphere
Paenibacillus for vegetables
Azospirillum for vegetables
Auburn - Pseudomonas and Bacillus for vegetables
Genetically Modified Bacteria

Other Beneficial Bacteria:

Links to general bio-control research:

AGRIBUSINESS - bio-control agents
History of Modern Biotechnology - growth stimulants
Growth Promoting Rhizobacteria
EPPO - bio-controls
Streptomyces lydicus:

Streptomyces lydicus is a saprophytic Actinomycete which suppresses harmful fungus. Especially useful on okra against cotton root rot. Originally isolated from flax roots.

Bacteria for plant growth promotion.

Chitin is a compound found in shell of crab, lobster, shrimp, snail, fish scale, etc. It will encourage Streptomyces lydicus which will suppress harmful fungi.

Science Direct
Atlantic Cool Climate Crop Research Centre - crab leg to suppress wart disease
Azospirillum brasilense:

Azospirillum brasilense stimulates nutrient uptake in plants.

Crown Gall:
Agrobacterium radiobacteria - prevent certain types of crown gall
Agrobacterium radiobacteria - Pacific Northwest crown gall

Mycorrhiza helper bacteria (MHB) examples: Ralstonia basilensis, Bacillus subtilis, Pseudomonas, Streptomyces, etc.

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