Worm Tea and Aquaponics—Brief Backgrounder

Summary of current scientific findings on why worm tea should be used as well as what is worm tea.

Why use worm tea?

There are many reasons to use worm tea:

• producing nutrient rich fertilizer from animal waste can not only reduce negative pressures on environmental ecosystems but increase agriculture productivity as well; 
• specifically, worm tea contains a myriad of soluble nutrients[i], e.g. potassium, magnesium, growth enhancers, e.g. auxins[ii], humic acids[iii], and fulvic acids[iv], enzymes, e.g. cellulose, chitinase[v], and microorganisms, e.g. bacteria, fungi, and pseudomonads[vi];
• there is some evidence that worm teas can suppress some plant pathogens[vii] and in fact there is a patent for the methods of using worm tea as an insect repellent[viii]; 
• worm tea, unlike vermicompost, probably won't clog any aquaponic system's pump; and
• best of all, worm tea is neither difficult nor expensive to produce—you could probably do it. 

Different types of "worm tea"

Vermicomposting leachate/vermin-leachate, worm bed leachate, vermiwash, and worm tea[ix], which comes from vermicomposting[x], are commonly interchanged terms but scientifically speaking they are substantially different—at least in their preparation[xi]. 

• Plants that were treated with vermiwash[xii], produced via the following method <http://www.youtube.com/watch?v=keg0Ia4y4_Y>, have been observed to have a higher concentration of chlorophyll and carotenoids than untreated controls[xiii].
• Vermicomposting leachate[xiv] is the seepage that comes from the vermicomposting reactor/bed, which is constantly supplied with water to maintain moisture. This resulting leachate theoretically contains the nutrients that have been mineralized and assimilated by earthworms and microorganisms[xv]. After being applied with vermicompost leachate, plants have demonstrated high germination percentage and improved growth indices versus untreated controls[xvi]. 
• Vermicompost aquaeous extract[xvii] or “true worm tea” is commonly made by placing vermicompost into a fixed amount of water, stirred occasionally, and allowed to sit for seven days[xviii]. Some scientist have aerated this mixture or similar mixtures to ≥5mg oxygen/L while adding other products, e.g. sugar, grain, humic acid, to enhance microbial activity[xix]. Both methods seem to improve strawberry yield, though aeration showed superior performance versus non-aerated, and suppress the necrotrophic fungus Botrytis cinerea[xx]. 

Some have thought that worm tea may be the best of the three aforementioned liquid vermicompost products, though formal scientific comparison of the three liquids on plant growth has not been conducted yet, because of many reasons such as aerobic microbes don't produce foul smells and a more biologically active solution is more conducive for plant growth.

For worm tea production, application, and further comments press here.

Endnotes

[i] ER Ingham, The Compost Tea Brewing Manual, 5th edn (Oregon: Soil Foodweb Incorporated, 2001), p. 37 <http://washington.osu.edu/cuyahoga/topics/agriculture-and-natural-resources/cuyahoga-composts/Compost%20Tea%20Brewing%20Manual.pdf> [accessed 15 January 2014].
[ii] RM Atiyeh and others, ‘Effect of Vermicompost and Compost and Compost on Plant Growth in Horticulture Container Media and Soil.’, Pedobiologia, 44 (2000), 579–590 <http://www.researchgate.net/publication/222678400_Effects_of_vermicomposts_and_composts_on_plant_growth_in_horticultural_container_media_and_soil/file/79e41510824e3421c4.pdf> [accessed 16 January 2014].
[iii] A Muscolo and others, ‘Earthworm Humic Matter Produces Auxins-like Effect on Daucus Carota Cell Growth and Nitrate Metabolism.’, Soil Biology and Biochemistry., 31 (1999), 1303–1311 <doi:http://dx.doi.org/10.1016/S0038-0717(99)00049-8>.
[iv] Shlrene Quaik and others, ‘Potential of Vermicomposting Leachate as Organic Foliar Fertilizer and Nutrient Solution in Hydroponic Culture: A Review’, Asian Journal of Plant Sciences, 7 (2008), 360–367 (p. 3) <doi:10.7763/IPCBEE. 2012. V44. 10>.
[v] S Subler, Clive A. Edwards and J Metzger, ‘Comparing Vermicomposts and Composts’, BioCycle, 39 (1998), 63–66.
[vi] Ingham, p. 43.
[vii] Linda Chalker-Scott, ‘The Myth of Compost Tea Revisited: “Aerobically-Brewed Compost Tea Suppresses Disease”’ (Puyallup Research and Extension Centre, Washington State University, 2014), p. 3 <http://puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Compost%20tea%20again.pdf> [accessed 8 January 2014].
[viii] George E. Hahn, ‘Method of Using Worm Castings for Insect Repellency’ (Cardiff by the Sea, 2002), p. 6 (p. 1) <http://patentimages.storage.googleapis.com/pdfs/US6797507.pdf> [accessed 17 January 2014].
[ix] SA Ismail, ‘Vermicology: The Biology of Earthworms’, Orient Longman Ltd, 1997, 92 (p. 92).
[x] FA Gutierrez-Miceli and others, ‘Optimization of Vermicompost and Worm-Bed Leachate for the Organic Cultivation of Radish’, Journal of Plant Nutrition, 34 (2011), 1642–1653 <doi:10.1080/01904167.2011.592561>.
[xi] Shlrene Quaik and Mahamad H. Ibrahim, ‘A Review on Potential of Vermicomposting Derived Liquids in Agricultural Use’, International Journal of Scientific and Research Publications, 3 (2013), p. 2 <http://www.academia.edu/3196238/A_Review_on_Potential_of_Vermicomposting_Derived_Liquids_in_Agricultural_Use> [accessed 14 January 2014].
[xii] Ismail.
[xiii] Quaik and Ibrahim, p. 2.
[xiv] Gutierrez-Miceli and others.
[xv] Gutierrez-Miceli and others.
[xvi] Quaik and Ibrahim, p. 3.
[xvii] Archana Pant and others, ‘Vermicompost Extracts Influence Growth, Mineral Nutrients, Phytonutrients and Antioxidant activity in Pak Choi (Brassicarapa Cv. Bonsai, Chinensis Group) Grown under Vermicompost and Chemical Fertilizer’, Journal of Science of Food and Agriculture, 89 (2009), 2383–2392 <doi:10.1002/jsfa.3732>.
[xviii] Quaik and Ibrahim, p. 4.
[xix] Ingham.
[xx] Sylvia E Welke, ‘The Effect of Compost Extract on Yield of Strawberries and Severity of Botrytis Cinerea.’, Journal of Sustainable Agriculture, 25 (2005), 57–68 <doi:10.1300/J064v25n01_06>.