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Re: Regulation of compost teas
For those of you interested in learning about the microbiology of compost teas, you might want to read the Compost Tea Brewing Manual, from Soil Foodweb Inc. in Corvallis, OR.
With respect to organisms in tea, white sugar is rarely used, as it selects for ess-than-wonderful species of bacteria. Blackstrap molasses with no sulfur, is more common, since it contains a much wider diversity of sugars, along with a bit of fungal food.
Fish emulsion is a good food to grow some very diverse bacteria, and improves several groups of quite beneficial bacteria. But more important than these additives are the soluble materials that come out of the compost. They enhance the growth of quite a few beneficial species of bacteria.
We need to be careful that we are discussing AEROBIC compost, not putrefying organic matter. Species diversity is quite limited in putrefying materials. And unfortunately, that is the material often mistaken for compost by academics who don't know what real compost is.
By definition, composting is an aerobic process, producing microbial biomass, some metabolic wastes and carbon dioxide. Anaerobic digestion leaves a good 25 to 50% of the carbon present as organic matter - stinky, smelly organic matter in many cases..
So, aerobic, ok? If you have aerobic conditions, then you have MANY species of microorganisms, up to as many as 25,000 unique DNA sequences from a gram of compost.
We use morphological methods as well, and have come up with as many as 20,000 unique morphological types of bacteria and fungi in a gram of compost as well.
Plate counts don't even get you close to that, because, as Joel Gruver points out, most of the organisms in soil, or compost or compost tea can't grow on lab media. We don't know the mix of foods, temperatures and moistures/humidities they need to grow. Thus using plate count approaches is nonsensical for assessing numbers or species diversity in environmental samples. To grow an organism for whom you know their growth conditions, then that's a different story. But we only know this for a few species of bacteria and fungi.
Aeration in tea is needed to set up conditions that select against human pathogens (which require reduced or low oxygen conditions), against plant pathogens such a Pythium and Phytopthora, Rhizoctonia and Fusarium, which do better in oxygen reduced conditions. Reduced oxygen allows these diseases to be competitive, while in fully aerobic conditions, they cannot out-compete or inhibit anyone else growing. That's why compacted soils have so many disease problems. The diseases are being helped out by the soil conditions.
The added foods help to grow some very beneficial species, at least species that researchers tout as beneficial. We see many fluorescent pseudomonads which produce the desired growth hormones, bacillus species that result in repulsion of many insect pests, nitrogen fixing bacterial species, and the species of bacteria that are especially good at decomposing recalcitrant carbon compounds, and pesticides enhanced as a result of the added foods.
Diversity of the kinds of carbon is important.
But simple occupation of space is critical too. If there is no space for the disease spore to reach the leaf surface, there is much less likelihood of disease. If the leaf surface is covered, then all the infection sites are occupied. If the leaf surface is covered, then all the foods the plant produces are used by the protective layer, and there is no food to grow the pathogen. So, multiple mechanisms of control. Let us not rely on just one.
All the species possible, completely covering the leaf, blossom, bark, etc. We have some astounding results in protecting plants against disease, both on the leaf surface and the root surface.
So, yes, teas work better with aeration (suppress and get rid of the disease organisms), with the right foods (grow just the good guys), and with nutrients. But often the added nutrients are really for the plant. As the organisms grow on the leaf surface, they respire, and that elevated carbon dioxide causes the stomates to open, and the nutrients move into the plant more rapidly, for a longer time. Some impressive greening up as a result. Temperature is of course important, as is water, and other nutrients not limiting, but given those being ok, plants can show marked improvements.
I hope this helps explain what is going on with 24 hour compost tea. These are not slimy, smelly 3-week brews but they are 24 hour, aerobic tea brews. Cleaning the machine is extremely critical. Control of the quality of the tea maker is important. Testing is necessary. No human pathogens in the compost! Quality products in, quality out.
President, Soil Foodweb Inc, Corvallis OR
President, Soil Foodweb Institute, Lismore, Australia
Affiliate Faculty, Southern Cross University
Director of Research, Soil Foodweb New York
Director of Quality Assurance, Soil Foodweb Europe
(I was assistant and then associate professor at Oregon State University for nearly 15 years, but last December decided to go full time with SFI.)