Compost tea

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. [Zhang, W., Han, D. Y., Dick, W. A., Davis, K. R., and Hoitink, H. A. J. 1998. Compost and compost water extract-induced systemic acquiredresistance in cucumber and "Arabidopsis". Phytopathology 88:450-455.]

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.

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 [Tränkner, A. 1992. Use of agricultural and municipal organic wastes to develop suppressiveness to plant pathogens. in: Biological Control of Plant Diseases. E. C. Tjamos, G. C. Papavizas, and R. J. Cook,eds. Plenum Press, New York.] Today, DIY automated compost tea machines as well as compost tea brewing barrels are available commercially. [ [http://www.biocompost.eu/tea.php DIY automated compost tea machines] ] [ [http://www.growingsolutions.com/ Commercial compost tea brewing barrels] ]

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.

Anaerobic 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.

Aerobic Compost Tea (ACT)

The use of air pumps or blowers to aerate or brew compost tea. A compost of high quality is added to aerated water at the rate from 1:50 to 1:100 (1 part compost to 50-100 parts water). The water must have a sustained dissolved oxygen content of 6 ppm or higher to be able to support aerobic organisms and be considered an aerobic tea. Water may be warmed slightly but cooler water supports higher dissolved oxygen rates. By aerating the water the extraction and growth of beneficial bacteria, protozoa and fungi that were present in the tea is promoted. Teas are aerated from 12 to 48 hours depending what type of microbes are desired. A short brew of around 12 hours will favor the growth of fungi, while a 24 hour brew will favor the growth of bacteria and a long brew of 36-48 hours will favor the growth of protozoa. Some farmers will add small amounts of supplements that promote growth of these microbes. Molasses will promote the growth of bacteria while kelp and humic acid will promote the growth of fungi. Sometimes sphagnum peat moss or hay is added as a source of protozoa. After brewing is complete ACT should be applied to the field as soon as possible to ensure that the tea is applied to the soil when the microbes are most active. ACT is applied to the soil to boost populations of biology and increase the rate of biological activity in the soil. Sometimes ACT is sprayed on leaves as a disease preventative but the effectiveness of this application is debatable. It is important to use unchlorinated or dechlorinated water when making ACT, since chlorine will kill beneficial microbes.

Other teas

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.

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.

Bokashi Tea

Made by soaking bokashi in water, or by using bokashi instead of compost in an aerobic compost tea.

See also

* Effective microorganism
* Composting

References

^ Zhang, W., Han, D. Y., Dick, W. A., Davis, K. R., and Hoitink, H. A. J. 1998. Compost and compost water extract-induced systemic acquired resistance in cucumber and Arabidopsis. Phytopathology 88:450-455. ^ Tränkner, A. 1992. Use of agricultural and municipal organic wastes to develop suppressiveness to plant pathogens. in: Biological Control of Plant Diseases. E. C. Tjamos, G. C. Papavizas, and R. J. Cook, eds. Plenum Press, New York.

External links

* [http://cari.unl.edu/2003abstractpresentation/Scheuerell%20Presentation.pdf 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
* [http://www.ams.usda.gov/nosb/meetings/CompostTeaTaskForceFinalReport.pdf NOSB Compost Tea Task Force Report]
* [http://www.usl.uni-bonn.de/pdf/Forschungsbericht%2089.pdf German report: use of composts and compost-tea for disease control in organic farming]

* http://www.microbeorganics.com/#So_You_Wanna_Build_A_Compost_Tea_Brewer Build your own Compost Tea Brewer