C. 1. Understanding Compost Tea

1. Why Use compost tea?

Compost tea is used for two reasons: To inoculate microbial life into the soil or onto the foliage of plants, and to add soluble nutrients to the foliage or to the soil to feed the organisms and the plants present. The use of compost tea is suggested any time the organisms in the soil or on the plants are not at optimum levels. Chemical-based pesticides, fumigants, herbicides and some synthetic fertilizers kill a range of the beneficial microorganisms that encourage plant growth, while compost teas improve the life in the soil and on plant surfaces. High quality compost tea of will inoculate the leaf surface and soil with beneficial microorganisms, instead of destroying them.

What is compost Tea?

Compost tea is a liquid produced by leaching soluble nutrients and extracting bacteria, fungi, protozoa and nematodes from compost. The brewing process is performed at constant temperature, although the growth of the organisms may elevate temperature as a result of their reproductive heat produced.

Tea production is a brewing process, and as easy as making beer or wine. But we all know that wine or beer brewing isn’t that easy. Brewing compost tea can be fraught with problems. But if you think about what you are doing, and pick out the right tea-making machine, making compost tea that will help your plants is easy as flipping a light switch. What is your purpose in making tea? If you want to inoculate a highly beneficial group of bacteria and fungi, protozoa and possibly nematodes, buy good compost that has these organisms, and make Actively Aerated Compost Tea. There are a number of excellent tea makers on the market (see How to make AACT).

Benefits of using of compost tea containing the WHOLE foodweb include:

• Improve plant growth as a result of protecting plant surfaces with beneficial organisms which occupy infection sites and prevent disease-causing organisms from finding the plant,
• Improve plant growth as a result of improving nutrient retention in the soil, and therefore reduce fertilizer use, and loss of nutrients into ground- and surface waters
• Improve plant nutrition by increasing nutrient availability in the root system as predator-prey interactions increase plant available nutrients in exactly the right place, time and amounts that the plant needs,
• Reduce the negative impacts of chemical-based pesticides, herbicides and fertilizers on beneficial microorganisms in the ecosystem
• Improve uptake of nutrients by increasing foliar uptake as beneficial microorganisms increase the time stomates stay open, while at the same time reducing evaporative loss from the leaf surface,
• Reduce water loss, improve water-holding in the soil, and thus reduce water use in your system,
• Improve tillage by building better soil structure. Only the biology builds soil structure, and ALL the groups in the foodweb are required to be successful. You can’t have just bacteria, you must have fungi, protozoa, nematodes and microarthropods as well! Please be aware that plate count methods don’t tell you about the whole foodweb.

What is in compost tea?

Tea contains all the soluble nutrients extracted from the compost, but also contains all the species of bacteria, fungi, protozoa and nematodes in the compost. Not all the individuals in the compost, but representatives of all the species in the compost are found in the compost tea. Making sure only beneficial species are present in the compost is therefore critical.

Outdated methods of assessing numbers of organisms in samples might lead you to believe compost tea doesn’t have much diversity. But, consider that species diversity in soil is much, much greater than plate count data would lead people to believe. Plate counts miss 99.99% of the bacterial and fungal species in soil. You need to use molecular methods to understand true species diversity in compost.

Plate count assessments of diversity in compost and tea, and soil should not be used. They are misleading about the true diversity, or even as an indicator of diversity in soil, compost or compost tea. Good, aerobic compost contains a huge diversity of organisms.

Foods extracted from the compost, or added to the tea, grow beneficial organisms. A large diversity of food resources is extracted from compost. The species diversity of organisms in the tea is much higher than those hundred or so species of bacteria that grow on the food resources added by people. Together, the beneficial bacteria and fungi growing on the compost foods, and on the added foods, result in a many individuals of many different species. Molecular diversity analysis is required, however, to assess even a small portion of the species present in compost tea.

Only aerobes are desired. Anaerobes make alcohols that kill plant tissues very rapidly. Putrifying organic matter, which is anaerobic, also contains organisms, just not organisms that do anything beneficial for your plants.

Most introductory microbiology books can answer most questions about the controversy between direct enumeration and plate count approaches. Reading the sewage treatment literature also points out clearly the conditions that allow E. coli to grow, which means reduced oxygen atmosphere. In full aerobic conditions, only if the beneficial bacteria have been killed or harmed can E. coli win in competition with aerobic organisms.

The list of papers specific to compost tea and compost have been summarized by Steve Diver, and are listed on the ATTRA website, www.ATTRA.org

When buying a tea machine, you should ask the manufacturer to provide information about oxygen during the tea brewing cycle in the compost basket or bag. You should insist on being given molecular analyses of diversity, and total and active bacteria and fungi, and protozoa, present in the tea made under standard conditions.

The METHOD is critical in making tea

In order to have the organisms in the tea, brewing conditions must be correct to produce the end product desired.
The biology that is active and performing a function will be very different, depending on:

• temperature of brewing,
• the foods added to the brew,
• oxygen concentrations in the brewer during production,
• the initial compost used, and therefore which species are present to be extracted,
• The length of time tea is brewed.

Temperature

Temperature during brewing should be related to the temperature of the soil, or of the leaf surface. If tea is applied in the late autumn, when temperatures are cool, it may be wiser to apply a tea where the organisms are mostly asleep, or that are selected to grow on plant residues. Selection for this ability would be enhanced by addition of plant material to the brew, such as oatmeal, alfalfa meal, feathermeal, etc.

Foods

Foods added to a brew will select for particular species that can use those foods. Do you want a bacterial tea? Add sugars, simple proteins, simple carbohydrates. If a fungal brew is desired, add more complex foods, such as plant material (oatmeal, soybean meal, flour), humic acids, fulvic acids (which will release bacterial foods after fungi begin the process of decomposition). Predators can be enhanced by adding hay (cut green and dried), or by soaking hay for a few days and adding the water to the tea brew.

Oxygen

Oxygen is perhaps the parameter that has been least understood in centuries of tea-brewing. Most beneficial organisms, the organisms that promote the processes that plants need in order to grow without stress, and therefore with greatest resistance to disease, are aerobic organisms. To enhance this community of beneficials, tea must remain aerobic.

Fermentative microorganisms are organisms which can grow in aerobic as well as reduced oxygen conditions. Since these organisms have dual metabolic abilities, they have to maintain the genetic material for both sets of enzymes. They have an energetic load that means they are not as competitive with true aerobes, when oxygen is in fully aerobic concentrations. They are not as competitive when in competition with true anaerobes at low oxygen concentrations. They do best in the conditions where oxygen is fluctuating in the intermediate aerobic – anaerobic range. These organisms can make very interesting waste products when growing in anaerobic conditions. These materials are known to have significantly inhibitory effects on a variety of less-desirable organisms.

The problem is maintaining the conditions exactly correctly so that the desired organisms grow. This knowledge is not public domain, and remains proprietary. Until attention is directed to understanding what products result from different aerobic – anaerobic conditions, with which foods, and with different temperature regimes during brewing, fermentative compost teas remain in the questionable realm. These teas don’t produce the same effects time-after-time, which is the reason that compost teas have languished in the “snake-oil”, and “voo-doo-juice” category for so long. If the tea you brew today has one effect, but the tea you brew tomorrow has a different, and possibly negative effect, that lack of reliable results will destroy the reputation of a product. It is most important to clearly maintain production conditions when making tea.

Anaerobic conditions (below 2 to 4 mg oxygen per L for example) during brewing can result in the growth of some quite detrimental microbes and production of some very detrimental metabolites. It is best to avoid extremely low oxygen concentrations during brewing, or if low oxygen concentrations occur, brewing must continue until the organisms stop growing on the added foods, such that oxygen will diffuse back into the brew. Only after the brew returns to the aerobic conditions should it be used on plants or soil.

If you want to make a mix of unknown, but possibly quite anti-bacterial, or anti-fungal materials, then a fermentative approach might be best. The specific conditions needed for production of a consistent mix set of inhibitory substances are not well-documented. More work is needed to understand production parameters for this kind of tea.

Is compost or compost tea "better" if it is aerobic or anaerobic?

Bacteria that cause human diseases almost invariably require anaerobic or reduced oxygen conditions in order to survive in competition with aerobic organisms. Only in reduced oxygen, or anaerobic conditions, can human disease-causing organisms out-compete the normal set of beneficial bacteria or fungi growing in soil, compost or compost tea.

If you’ve done a good job choosing or making your compost, the compost will not contain any human disease organisms. The tea will not contain human pathogens if there were none in the compost. What do you need to know in order to be assured that the compost contains no human pathogens? The temperature cycle of the compost. Insist on getting that data from the compost maker. What do you care about the amount of nitrate, if there are human pathogens in the “compost”?

If the compost was kept fully aerobic, and temperatures between 135 F and 155 F were maintained for 10 to 14 days, or the compost was processed by adequate numbers of earthworms, the likelihood of human pathogens in the compost is just about nil. Contamination of finished compost by something else containing pathogens is possible so be aware that this can be a problem too.

If the compost wasn’t processed correctly and disease-causing organisms weren’t destroyed by temperature, competition with beneficial organisms, or passage through earthworms, the probability is reasonable that disease-causing organisms will grow rapidly and be in high numbers in a tea that goes through reduced oxygen, or anaerobic, conditions.

If the tea was made with good compost (high numbers of beneficial bacteria, fungi, protozoa, nematodes; good soluble nutrients) using aerobic conditions, there is little likelihood that human pathogens could grow, because not only are conditions not correct for their growth, but they will be out-competed and inhibited by the aerobic bacteria and fungi growing in those aerobic conditions.

It is critical to know that the tea maker you are using can maintain aeration rates greater than the rate the bacteria and fungi use up the oxygen.

Oxygen or carbon dioxide can be monitored to determine whether aeration is adequate throughout the whole brewing cycle, and in all parts of the machine. Please be aware that the data needed are from the inside of the compost basket, or inside the compost bag. Currently, all national level compost tea manufacturers display SFI data on their websites, with only two exceptions. People who bought machines from these two companies have sent data to SFI showing that either inside the compost baskets or the bags, the tea went anaerobic during tea brewing, or serious anaerobic bio-films develop in places that you can’t see or can’t reach easily during cleaning.

Oxygen in the tea should not fall below 5.5 to 6 ppm dissolved oxygen, which is typically about 70% dissolved oxygen, or 15 to 16% oxygen when measuring total atmospheric gases. These values change based on altitude and temperatures, so make sure the oxygen probe comes with information on typical maximum oxygen levels, which is where your water in your tea maker will start out.

You can’t tell whether oxygen use, or carbon dioxide production, was performed by bacteria or by fungi. Since you need to know, at least occasionally, the ratio of fungi to bacteria your tea, you need to test your teas so you can be certain you are making disease suppressive tea.

Fungi grow very well indeed in compost tea.

For good fungi in tea, first of all, fungi in the compost have to be extracted adequately. This is a function of two things, presence in fungi in the compost, and rapid enough water movement through the compost to pull the fungi off the compost particles. Work with Bruce Elliott of EPM (sales@composttea.com) has shown how easy it is to get great extraction and growth of fungi in the tea.

The EPM, KIS, WormGold, and BnBrewer machines in the US, Tea-riffic® in Canada, the Compost Tea machine in New Zealand, and Compara in Europe, in do excellent jobs of extracting fungi from the compost and allowing it to grow in the tea. Testing, over one to two years, shows that these machines continue to make good tea. Machines with hidden surfaces that develop biofilms do not maintain good tea production over time.

Sales people from companies that cannot pass SFI standards like to say that “fungi don’t grow in tea”, or “there are lots of fungi in the soil already”. Please realize that what they are actually telling you is that the machines they sell do a poor job of extracting fungi and growing fungi. Fungi can be extracted and grow quite well in tea.

When soils have been treated with fungicides, including copper sulfate, or sulfur, the soil cannot possibly maintain normal levels of beneficial fungi. Adequate beneficial fungal biomass does not occur in any field treated with fungicide, insecticide, bactericide, nematicide, herbicide or high levels of inorganic fertilizer.

Fungi require foods to feed them

If the compost contains complex food resources, that can be enough to feed many fungal species, but usually additions of humic acids, and complex nutrient resources enhance the growth of beneficial species. People involved in making tea often research nutrient food resources. Hendrikus Schraven Landscaping (gina@hendrikusorganics.com), EPM (sales@composttea.com) and Leon Hussy at KIS (www.simplici-tea.com) make some outstanding food resources for bacterial and fungal teas. Many ideas for foods for bacteria and fungi can be found on the compost_tea list serve, www.compost_tea@yahoogroups.com

Species diversity

Species diversity is the same in compost and the tea made from that compost. Species diversity in compost is higher than fumigated or sick soil. But at least one plate count microbiology lab is giving out data suggesting that compost has lower diversity than bad soil and that “ok” tea has less diversity than bad compost. It is clear that plate count “diversity” methods are not effective in assessing species diversity, or species richness, in soil, compost or compost tea. Molecular methods tell us that species diversity in soil, tea, and compost, can number in the thousands and tens of thousands per gram.

Use of methods that tell you that soil contains only a few 5 to 10 species, or that compost contains only 8 to 15 species need to be viewed with a great deal of incredulity. Plate methods are missing only about 99.9% of what is actually present!

Do plate counts or direct counts assess tea quality? The clear answer is that direct counts assess tea quality, while plate counts do not. Take a look at the results (below) from a test where two different teas were used to control blight on tomato plants.

Compost bags

Multi-layer fabric, or felt, bags are a poor idea, because the hyphae get held in the fabric, and mildew grows in the damp material. Single layer, nylon or netting bag material is necessary.

Time to brew

Small, well-aerated, well-mixed compost tea makers can give great tea within 10 to 12 hours. The KIS machine gets great organism extraction and growth of the beneficial organisms in 12 hours, based on direct counts of the individual bacteria, measurement of biovolume of fungal hyphae, enumeration of protozoa and nematodes from those teas.

Pay attention when you buy a machine or develop a design. Different tea machines take different amounts of time to brew good tea. Especially those machines that take 48 hours or more to brew a decent level of organisms in their tea, the salespeople tend to be very reluctant to tell you exactly how long the tea takes to reach a certain organisms-in-the-tea level. For example, some machines take a minimum of 48 hours to brew the tea, and as a result, tend to have more problems with becoming anaerobic.

Several “tea-brewer” manufacturers have no data about maximum bacterial or fungal production with their machine, and certainly no clue at all about protozoa or nematode numbers. Their salespeople will tell you their tea is ready in 24 hours, but they don’t have any data to prove this to you. Buyer beware!

What is the shelf life of compost tea?

The shelf life is short in high quality tea with active organisms necessary to attach to lead surfaces and not be washed off. In the research that we have done with 24 hour brewing cycles, after just 6 hours without any aeration, the oxygen levels are lowered by over 300 %. If the compost tea is not used within that time, aerate, agitate and add more food to the tea to feed the micro-organisms.

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