Compost tea

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Compost tea, a liquid solution or suspension made by steeping compost in water. It is used as both a fertilizer and in attempts to prevent plant diseases.^[1]

Contents 1 Mode of action 2 General preparation 3 Types 3.1 Modern compost teas 3.2 Actively aerated compost tea 3.3 Fermented compost tea 4 Other teas 4.1 Compost leachate 4.2 Manure tea 5 See also 6 References 7 External links

[edit] Mode of action

There is considerable interest - and confusion - regarding the mode of action of compost teas. The biology of the tea and its effect in the plant phyllosphere are complex. The tea may be rapidly deactivated when foliar applied due to sunlight, rain and especially UV radiation. However, on the soil surface, the microbes in the tea will colonize plant litter and debris, and improve decay rates. Vineyards in the Alsace region of Germany and France reported significantly reduced fungal spore counts in the spring, after applying compost extracts - prepared in the European fashion - directly to the litter layer in the prior fall. Successful colonization, competition to foodstuffs, antibiotic effects, and systemic effects, all belong to the arcana of possible biochemical mechanisms that make compost teas potentially biologically active materials.

[edit] General preparation

Made by steeping compost in water for a variable period up to 5-days, then applying the liquid un-diluted as a spray to non-edible plant parts, or as a soil-drench (root dip), such as to seedlings, or as a surface spray to reduce incidence of harmful phytopathogenic fungi in the phyllosphere ^[2] Today, DIY automated compost tea machines as well as compost tea brewing barrels are available commercially.^{[3] [4]}

[edit] Types

There are several kinds of compost tea, depending on the method and ingredients with which the tea is made. In Europe compost teas are largely distinguished on the basis of whether or not they have manure content, the latter preferred for having more consistent disease suppressive capabilities.

[edit] Modern compost teas

These consist of controlled compost extracts made by adding finished, properly prepared compost to water and stirring the mix for 1 - 14 days. This process encourages the loosening of microbes adhering to compost and soil particles so they are transferred into the water itself. The notion that compost tea is a "brew" process is of only recent origin in the USA. Traditional compost tea (called compost extracts) developed in Europe and especially in Germany by microbial scientists from the late 1970's on, did not employ significant technological support to prepare solutions of compost with microbial counts as high as 10¹¹ per ml. The mixing, or active aeration, was required after the introduction in the USA of molasses, sugars and other highly fermentable agents created fermenting, anaerobic conditions; as a direct result, it became necessary to take extra steps to maintain compost teas in an aerobic condition, to be safe and non-odorous. If the tea is properly made, it is a mixed concentrate of facultative and aerobic microbes, and presumed non-harmful. The US National Organic Program (National Organic Program) has strict guidelines on use of compost teas in USDA certified organic farming; research evaluated by a Tea Task Force did not support the idea that active vs non-active teas had any differences in terms of microbial hygiene, and therefore the need to protect the safety of organic consumers and the integrity of organic farming became necessary. For example, E. coli testing of compost extracts is strongly recommended and may be required under NOP; the levels should be less than 126 cfu ml-1.

Traditional European formula: Steep 1 part compost in 3 : 9 parts water, with optional additions of a handful of basalt-meal or granite-dust and seaweed powder, and stand at room temperature ( 20 - 25C°) for 3 - 24 days, with frequent stirring. Sieve through cheesecloth or a fine mesh screen.

[edit] Actively aerated compost tea

The use of mechanical equipment to actively aerate compost tea. An Actively Aerated Compost Tea [AACT] implies a focus on stirring and aeration, but is more expensive and complicated to carry out. Recent results published in the Journal of Food Protection ^[5] suggest that both kinds of teas - active and non-active- can allow reproduction of potentially pathogenic E. coli provided ample available substrate is present; regardless of the aeration. Since "E. coli" is a facultative organism, aeration alone is not a preventative for its continued reproduction. This misunderstanding, in the minds of many scientists, harmfully promoted by the "ACT" community, goes to the heart of understanding of the real use and effects of compost teas.

[edit] Fermented compost tea

Known somewhat incorrectly as anaerobic compost tea, this occurs by leaving compost and water in a container for a period of several days, allowing oxygen levels to drop well below 0.2% dissolved oxygen encouraging anaerobic microbial growth. This rarely happens in nature unless a container is sealed from the air. Moreover, if too much sugars or readily available carbohydrates are added to the tea, as is recommended in some popular literature, even active aeration will not prevent odorous developments nor the reproduction of E.coli. The loss of aerobic microbial diversity therefore is mostly dictated by presence or absence of readily available foodstuffs.

[edit] Other teas

[edit] Compost leachate

Compost leachate is the liquid that drains out of compost when it is overly-moist (i.e at or above saturation). In Europe and North America, environmental agencies have shown concern for the leachate from compost facilities, as it escapes to surface water. Leachate carries a large quantity of dissolved organic matter, bacteria, and potassium ions. As such, it is not a compost tea nor should be used as such, largely because it may represent the result of overly-wet and potentially anaerobic conditions.

Compost "leachate" is produced when water or humidity runs through a saturated compost heap. The liquid consists mainly of enzymes, hormones and soluble nutrients extracted from the compost. This "leachate" boosts plant growth by "building" the soil's structure, raising the percentage of nutrients in the soil and improving its water-retention capacity.

[edit] Manure tea

This type of "tea" occurs in the early literature in some very early pre-WWII variants of organic farming, and is not known to be an actual practice. On farms with urine drainage systems, manure will produce a form of manure tea which can become anaerobic, but is popularly used as "slurry fertilizer", in Germany Gǖlle. Using raw manure is potentially more risky as there are more viable forms of pathogenic organisms present, so the land application must be practiced more carefully. However, the majority of the world still uses manure in a raw and semi-liquid states and it has proven safe when properly managed within farming systems.

[edit] See also

• Effective microorganism
• Composting

[edit] References

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (July 2007)

[edit] External links

• How to make compost tea
• DIY Automated compost tea machines
• Compost Teas for Plant Disease Control: Production, Application, and Results ASA-CSSA-SSSA Annual Meeting, Denver, CO, Nov. 5th, 2003 Steven Scheuerell and Walter Mahaffee, Department of Horticulture, Oregon State University
• NOSB Compost Tea Task Force Report
• German report: use of composts and compost-tea for disease control in organic farming