Microbial Content of Actively Aerated Compost Tea after Variations of Ingredients or Procedures

Compost tea describes a procedure where compost is mixed with water. The mixture may be left to stand with minimal disturbance, also called “compost extract” or “steepage”, or actively supplied with oxygen by an aquarium pump to stimulate population growth of aerobic microbes. This project examined actively aerated compost tea. Over a 3-year period, 25 experiments were conducted where a standard recipe was compared to variations of ingredients or procedures. Identification and count of microbial content was done by direct microscopy. The “standard recipe” was 15 litres of tap water (pH 7.0), 485 grams of composted yard waste, 285 grams of commercial worm castings, 30 ml of humic extract, 30 ml of commercial kelp Ascophyllus nodosum and 30 ml of fish fertilizer. The procedure was to aerate water for 60 minutes in a commercial brewer, add ingredients which are removed after 5 hours, then maintain brewing for another 17 hours at room temperature of 20C. Results indicate that longer brewing time increased protozoa activity; addition of humic acid stimulated fungi activity; addition of kelp stimulated protozoa activity; addition of fish fertiliser stimulated fungi activity and increased nutrient content; use of worm castings resulted in increased fungi content; and mixing protein food with compost ahead of brewing resulted in higher protozoa activity. However, replicated experiments were difficult as the microbial content changes continuously over time and it was not possible to measure accurately a large number of samples in a short period. INTRODUCTION Non-aerated compost tea describes procedures where compost is mixed with water and left to stand for many days with minimal disturbance. It has been used for many years in agriculture and has also been called “extract”, “slurry” or “steepage” (Quarles, 2001). A frequent procedure is to mix compost with water in a volume ratio of 1:5, place in an open container, stir once then allow to sit for 10 days (Elad and Shtienberg, 1994) or stir twice during a 7-day incubation period at 20 to 22C (Al-Dahmani et al, 2003). Non-aerated compost tea applied as foliar sprays can provide adequate control of plant diseases such as grape powdery mildew (Trankner, 1992). Consistent and significant suppression of grey mold (Botrytis cinerea) on geranium was obtained with tea made from composted chicken manure or composted yard waste, but adding nutrients did not help with disease suppression (Scheuerell and Mahaffee, 2006). Non-aerated compost tea favours the extraction of antibiotic compounds that play an important role in suppression of plant pathogens (Cronin et al, 1996). Micro organisms may also be important as heat treatment of finished tea eliminated disease suppressiveness of grape powdery mildew, bean mould and tomato late blight (Scheuerell and Mahaffee, 2002). Actively aerated compost tea is more recent. The mixture of compost and water is supplied with active aeration, for example by an aquarium pump. The high oxygen concentration stimulates population growth of aerobic microbes which help with disease prevention, nutrient cycling and soil structure. By contract, these beneficial microbes may not survive in non-aerobic compost tea because of anaerobic conditions (Ingham, 2005). Actively aerated applied as a drench was effective to suppress damping-off (caused by Pythium ultimum) of cucumbers grown in soiless greenhouse media. Kelp and humic acids alone did not suppress damping-off, but triggered disease suppression when added to any of three different types of compost. Diluting the finished tea with water, or imposing heat treatment significantly reduced suppression, indicating the impact was related to microbes but not nutrients (Scheuerell and Mahaffee, 2004). This project examined actively aerated compost tea. It followed a field trial where weekly applications provided inconsistent control of powdery mildew of apple trees in commercial organic orchards (Lanthier and Peters, 2006). MATERIALS AND METHODS Over a 3-year period, 25 experiments were conducted inside a laboratory in Kelowna, British Columbia (elevation 1000 meters). Actively aerated compost teas were prepared using the commercial brewers “Bobolator” (North Country Organics, Vermont, http://www.dirtworks.net/Images/BrwrManBitti-1.pdf) and “Keep It Simple, Inc.” (Redmond, Washington, http://www.simplici-tea.com/). Each brewer came equipped with an aquarium-type pump to supply the appropriate amount of oxygen into the container. Each experiment was based on a “standard” compost tea. For the procedure, a 5 US gallon brewer was filled with 15 litres of water (drinking water from City of Kelowna, British Columbia, pH 7.0, Electrical Conductivity 0.24, varying between 15 and 21C); the water was actively aerated for 1 hour then filled with the required additives; the compost products were removed after 5 hours and the tea actively brewed another 17 hours. After each brewing, equipment was cleaned thoroughly with hydrogen peroxide. The “standard” recipe was as follows: composted yard waste 485 grams (product Glengrow, City of Kelowna landfill, British Columbia); vermicompost 485 grams (Nurturing Nature Organics, Lake Country, British Columbia); humic acid 30 ml (Multi-dynamic Humic Extract, Tecologic Products Ltd., Calgary Alberta); kelp 30 ml (Turbo SE 0-4-4 from Ascophyllum n., Logic Alliance Inc., Kentville Nova Scotia); fish fertilizer 15 ml (Nutrifish SE 2-3-1, North Atlantic fish, Pioneer Organics, Nova Scotia). At each experiment, multiple brewers from the same manufacturer were started at the same time, following the same recipe and procedure, but one variable was tested for impact on final microbial content. Samples of finished tea were collected and sent via courier to Soil Foodweb Inc. Canada (Vulcan, Alberta, http://soilfoodweb.ca/). Laboratory analysis was conducted by direct microscopy 48 to 72 hours after sampling. Dilution plates were used to count number of individuals and staining of sub-samples to distinguish active organisms. RESULTS AND DISCUSSION One brew was recopied over 18 experiments for the “Bobolator” brewer (Table 1) and nine experiments for the “K.I.S.” brewer (data not shown). Microbial content of finished teas was used to assess consistency of the same person using the same brewer and the same recipe. Results for each brewer show fairly constant numbers of bacteria and fungi from experiment to experiment but high variation in protozoa numbers (flagellates and amoeba). Compost is added to compost tea to supply the majority of micro organisms such as bacteria, fungi and protozoa. In this project, results indicate higher total fungi in tea prepared with one compost source compared to other compost sources (Table 2). There were high variations in number of protozoa, but no difference in total bacteria or active fungi. Vermicompost is a result of earthworm’s activity to digest plant residue. In this project, results indicate highly variable results. Number of flagellates was lowest in the tea prepared with vermicompost only and highest in the tea prepared with a combination of composted yard waste and vermicompost (Table 3). Total fungi, active fungi and active bacteria were highest in tea prepared with vermicompost only. Compost can be “activated” ahead of brewing to increase fungal content, which is then transferred into the tea. In this project, longer pre-activation time resulted in a linear increase in the number of flagellates (Table 4). Number of fungi (active and total) was highest in tea prepared with compost activated for 8 hours before brewing. Using a larger amount of activating material resulted in higher number of fungi (data not shown). Total brewing time is established to maximize multiplication of micro organisms while food additives are available. In this project, one brew was prepared and samples collected at various times then stored in a refrigerator until laboratory analysis. Longer brewing time resulted in a linear increase in number of flagellates (Table 5). There was also a linear increase in number of total fungi, amoeba and ciliates, but no change over time in number of total bacteria or active fungi. Humic acid is a component of humus, along with fulvic acid and humin. It is added to compost tea as a “food source” to stimulate growth of beneficial fungi present in the startup compost. In this project, the “standard” recipe of 30 ml per 15 litres water resulted in the highest number of total fungi (Table 6). Number of active fungi was also highest in the standard recipe, but there was no treatment impact on number of bacteria, flagellates or amoeba. No fungi were recovered from another tea brewed with humic acid alone without compost (data not shown), indicating the humic acid did not contribute fungi to the tea. Cold water kelp (specifically Ascophyllum nodosum) is added to compost tea as a “food source” to stimulate growth of both bacteria and fungi, and to add nutrients for plant foliage and roots. In this project, the amount of kelp had no impact on total fungi except at the 4X standard rate (Table 7). Number of active fungi was also highest in the higher application rate, but there was no impact on number of bacteria, and number of flagellates was higher in all treatments with seaweed, regardless of the rate used. No fungi were recovered from tea brewed with kelp alone, in the absence of compost (data not shown). In other brews, increased aounts of fish fertiliser resulted in a linear increase in total fungi (data not shown). There was no treatment impact on bacteria, flagellates or amoeba. CONCLUSION Compost tea has potential to help suppress plant diseases. There is strong scientific evidence that actively aerated compost tea can prevent a number of plant diseases such as damping off and Botrytis mould. Best results are obtained when start-up compost is high quality. The active brewing aims to extract beneficial micro-organisms found in the start-up compost; ingredients such as humic acid and kelp aim to stimulate population growth. In this project, there was a high impact on final microbial content from the start-up compost and the duration of brewing time. There was a moderate impact from the use of humic acid and kelp. There was a low impact from the source of water and the clean-up of brewing equipment (data not shown). All experiments were controlled but not replicated, preventing statistical analysis of most data. The results should be viewed as trends rather than absolute, as similar brews done under different conditions would likely deliver different results. Replicated testing of compost tear microbial content is difficult. Microbial composition changes over time with changes in oxygen concentration and food additives. Different persons doing counts by direct microscopy may yield different results. Future work will require a method to stabilize microbial activity without affecting microbial composition. Literature Cited Al-Dahmani J.H. et al. 2003. Suppression of bacterial spot of tomato with foliar sprays of compost extracts under greenhouse and field conditions. Plant Disease. 87:913-919. Cronin M.J. et al. 1996. Putative mechanisms and dynamics of inhibition of the apple scab pathogen Venturia inaequalis by compost extracts. Soil Biol. Biochem. 28(9):1241-1249. Elad Y., Malathrakis N.E. and Dik A.J. 1996. Biological control of Botrytis-induced diseases and powdery mildews in greenhouse crops. Crop Protection. 15(3):229-240. Ingham E.R. 2005. The Compost Tea Brewing Manual (fifth edition). Soil Foodweb Incorporated. Corvallis OR. Lanthier M. and Peters S. 2006. Compost tea: Testing the field application of actively aerated compost tea for prevention of powdery mildew and improvement of soil microbial community in fruit tree production in British Columbia. Organic Sector Development Program Project #I0933. Certified Organic Associations of British Columbia. Vernon BC. Quarles W. 2001. Compost tea for Organic Farming and Gardening. The IPM Practitioner. 23(9):1-8. Scheuerell S. and Mahaffee W. 2002. Compost tea: principles and prospects for plant disease control. Compost Science & Utilization. 10(4): 313-338. Scheuerell S. and Mahaffee W.F. 2004. Compost tea as a container medium drench for suppressing seedling damping off caused by Pythium ultimum. Phytopathology. 94:11561163. Scheuerell S. and Mahaffee W.F. 2006. Variability associated with suppression of gray mold (Botrytis cinerea) on geranium by foliar applications of nonaerated and aerated compost tea. Plant Disease. 90:1201-1208. Trankner A. 1992. Use of agricultural and municipal organic wastes to develop suppressiveness to plant pathogens. P. 35-42. In: E.C. Tjamos, G.C. Papavizas and R.J. Cook (eds.), Biological control of plant diseases. Plenum Press, New York.