the fascinating world of bacteria

here's Bonnie Bassler's take on the subject of bacteria:

in the last post, we saw how to make a compost tea (the 24 hour recipe) which is essentially a way of moving bacteria and other microbes from the contents of the compost pile into a liquid that can be applied to our precious plants.

but is that the only method of improving the bacterial content of our soils?  compost teas is but one route to take, as caretaker of the organic realm:

Compost Teas vs. Compost Extracts

First, it may be helpful to share some common terminology and practices associated with compost teas. How do compost teas differ from compost extracts or compost leachates?

Compost Leachate

Compost windrow leachate—the dark-colored solution that leaches out of the bottom of the compost pile—most likely will be rich in soluble nutrients; but, in the early stage of composting it may also contain pathogens. It would be viewed as a pollution source if allowed to run off-site. Compost leachate needs further bioremediation and is not suitable or recommended as a foliar spray.

Compost Extract

Compost watery extract—made from compost suspended in a barrel of water for 7 to 14 days, usually soaking in a burlap sack—a centuries-old technique. The primary benefit of the extract will be a supply of soluble nutrients, which can be used as a liquid fertilizer.

Compost Tea

Compost tea, in modern terminology, is a compost extract brewed with a microbial food source—molasses, kelp, rock dust, humic-fulvic acids. The compost-tea brewing technique, an aerobic process, extracts and grows populations of beneficial microorganisms.

Summary

Compost teas are distinguished from compost extracts both in method of production and in the way they are used. Teas are actively brewed with microbial food and catalyst sources added to the solution, and a sump pump bubbles and aerates the solution, supplying plenty of much-needed oxygen. The aim of the brewing process is to extract beneficial microbes from the compost itself, followed by growing these populations of microbes during the 24- to 36-hour brew period. The compost provides the source of microbes, and the microbial food and catalyst amendments promote the growth and multiplication of microbes in the tea. Some examples of microbial food sources: molasses, kelp powder, and fish powder. Some examples of microbial catalysts: humic acid, yucca extract, and rock dust.

Liquid Organic Extracts vs. Compost Teas

Building on the concept of compost teas as a liquid organic extract, what are some other common organic extracts used as a liquid drench or foliar spray?

Manure Tea

Manure-based extracts—a soluble nutrient source made from raw animal manure soaked in water. For all practical purposes, manure tea is prepared in the same way as the compost extracts described in the preceding section. The manure is placed in a burlap sack and suspended in a barrel of water for 7 to 14 days. The primary benefit of the tea will be a supply of soluble nutrients, which can be used as a liquid fertilizer.

Herbal Tea

Plant-based extracts—stinging nettle, horse tail, comfrey, clover. A common method is to stuff a barrel about three-quarters full of fresh green plant material, then top off the barrel with tepid water. The tea is allowed to ferment at ambient temperatures for 3 to 10 days. The finished product is strained, then diluted in portions of 1:10 or 1:5 and used as a foliar spray or soil drench. Herbal teas provide a supply of soluble nutrients as well as bioactive plant compounds.

Liquid Manures

Mixtures of plant and animal byproducts steeped as an extract—stinging nettle, comfrey, seaweed, fish wastes, fish meal. Liquid manures are a blend of marine products (local fish wastes, seaweed extract, kelp meal) and locally harvested herbs, soaked and fermented at ambient temperatures for 3 to 10 days. Liquid manures are prepared similarly to herbal tea—the material is fully immersed in the barrel during the fermenting period, then strained and diluted and used as a foliar spray or soil drench. Liquid manures supply soluble nutrients and bioactive compounds.

Summary

Compost teas and herbal teas are tools that can be made on the farm to enhance crop fertility and to inoculate the phyllosphere and rhizosphere with soluble nutrients, beneficial microbes, and the beneficial metabolites of microbes.

Caution

Wheareas raw animal manures are used as a compost windrow feedstock, the composting process—thermophyllic heating to 135-160° F for 10-15 days—assures pathogen reduction. The raw organic matter initially present in the compost windrow undergoes a complete transformation, with humus as an end product. Any pathogens associated with raw manures will be gone. So caution is extended: Manure teas are NOT the same thing as compost teas or compost extracts. Because of concerns over new pathogenic strains of E. coli, the author advises growers to reconsider manure teas and/or to work with a microbial lab to ensure a safe, worthwhile product.

references above are available from NCAT - National Centre Appropriate Technology

Microbial Inoculants: an Approach to Sustainable Agriculture

originally an article published here by Sunita Gaind, i thought i'd repost it, given there's a wealth of good information on the subject, which gives a broad overview:

The green revolution though made India self sufficient in food production, but at the cost of soil health. Persistent use of chemical fertilizers and low input of organic material in soil reduced its organic matter content, resulting in stagnation of food grain production by 1.5 %.

To restore the productivity of soil, efforts need to be focused on use of natural resources that can be an alternate to costly chemical fertilizers and restrict soil impoverishment. Current developments in sustainability involve the rationale exploitation of soil microbial activities and use of less available sources of plant nutrients. Nitrogen and phosphorus are the macronutrients that limit the plant growth. To meet the crop need, these are generally supplemented through chemical fertilizers. Soil inhabits microorganisms that possess the particular trait for nitrogen and phosphorus transformation. Their application to soil under crop cultivation can improve the nutrient availability; reduce the input of chemical fertilizer and a way to sustainable agriculture.

What are microbial inoculants?
Microbial inoculants are the formulations of beneficial living microorganisms that when added to soil, directly or indirectly, improve the nutrient availability to the host plant and promote plant growth. Microbial inoculants for biological nitrogen fixation are both strain and crop specific. However, phosphorus solubilization and mineralization can be mediated by potential isolates of bacteria and fungi. The latter being the key components of soil plant system can be developed as phosphate solubilizing microbial inoculants.

Fungi vs Bacteria as Phosphate solubilizeres
 Fungi maintain their P dissolving efficiency even on repeated sub culturing
 The extracellular production of phosphatase and organic acid is higher with fungi compared to bacteria. Therefore, fungi are more effective phosphate mineralizer/ solubilizers compared to bacteria.
 Their hyphae can travel long distance in soil more easily than bacteria and can prove more beneficial for solubilization of phosphorus in soil.
 They can tolerate low moisture, high temperature, heavy metals and agrochemicals.
 Their spore forming nature is an additional advantage for their survival under environmental stress.

How do microbes improve the availability of nutrients?
Soil microorganisms are involved in large number of processes that affect the P transformation and influence its availability to plant roots.
 By the excretion of hydrogen ions.
 By release of organic acids.
 By production of phosphatase enzymes that can mineralize soil organic P.
 Chelating metal ions that may be associated with complexed forms of P or may facilitate the release of adsorbed P through ligand exchange reactions.
 By displacement of sorption equilibria that results in increased net transfer of phosphate ions into soil solution or an increase in the mobility of organic forms of phosphorus.
 Growth stimulation through production of phytohormones.
 By production of siderophores.
 Phosphate dissolving fungi may also provide micronutrients for formation of polyphenol and other aspects of phenolic metabolism.
 Phosphate dissolving Trichoderma harzianum has shown the ability to accelerate the oxidative dissolution of metallic Zn.
 They also provide disease resistance to plants due to production of antibiotics and protection against soil borne pathogens.

Phosphate dissolving microorganisms used as microbial inoculants
Fungi: Aspergillus awamori, Aspergillus niger, Penicillium digitatum, Pencillium radicum, Penicillium bilaiae, Trichoderma koningii

Bacteria: Pseudomonas striata, Bacillus polymyxa, Bacillus megaterium, B.subtilis, B. circulans

Carriers: Charcoal- soil mixture, vermiculite, press mud, peat, cow dung cake powder, farm yard manure, wheat bran etc. Amendment of charcoal soil - mixture carrier with calcium alginate resulted in better retention of moisture.