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Re: Regulation of compost teas
Hi Dale -
But don't you think that after you leach into water, add molassas, and
aerate for a while you end up with a much simpler community? Adding a
soluble carbon source in a liquid culture is akin to a lab medium. I
don't mean to criticize the method, I just think it is simpler than
compost per se, and that plate counts might be a useful GC tool.
I have data on this. We see that all the species in compost will be extracted (it is not a leaching process in 24 hour compost tea) into the tea. If you have limited species diversity in the compost, you have limited species diversity in the tea. High diversity in the compost, high diversity in the tea.
But not all the individuals in the compost get extracted into the tea. So diversity in the tea isn't the same as diversity in the compost, but species richness is.
The food resources in the tea come from all the soluble nutrients and food resources in the compost, and there's a huge complexity there, not just the food resources you add, like a simple sugar. You are merely selecting for a group of highly beneficial bacteria or fungi by adding an additional food resource.
That's why testing is necessary to determine which set of beneficial bacteria and fungi are being enhanced by addition of any food resource. But plate counts don't even begin to give you those answers about numbers or diversity.
We did a comparison set of plate counts, and also did direct counts, and morphological counts. The plate counts gave 12 species of bacteria per gram of soil. Six different media were used. A total of about 30 different species on 6 different media. The molecular approach suggested 25,000 species, morphological analysis using direct counts gave us 20,000 different species (extrapolated from looking at 10 different fields and determining how many new species were observed in each field). The molecular approach is the way to do this work, but it's much too expensive right now.
Plate counts? Bio-log plates? Sorry. They don't even begin to get a handle on what is in soil, or compost, or compost tea.
We have a series of tests, including enzyme testing, GC work, and specific extractants that allow us to find whether the beneficial fungi and bacteria we know how to culture are present in a sample, and in how great numbers. We'll be offering that starting Nov 1 on the SFI website (www.soilfoodweb.com)
The only difference between compost and compost tea is that the non-soluble substrates start in the compost. So, yes, the food resources in the tea are lower than in compost, but every species in the compost is extracted into the tea.
Do all those species survive in tea? If you don't feed organisms the right foods, they tend to go to sleep and then die. No different than people. So, 24 hour, aerobic compost tea adds the whole diversity of organisms back into the soil, or onto the leaf surfaces. And they have enough food during that short time period to stay viable.
Addition of tea or compost to soil or leaf surfaces can be a huge benefit to both places, especially if your soil or leaf surfaces have been negatively impacted by pesticides or salts (better known as fertilizers).
If you had to guess, which species do you think are most
important in a good compost tea for disease control? It might be
possible to add small amounts of something, like adjust the pH, SO2,
iron, or a bit of benzakonium chloride, to tip the tea ecology one way
We're looking at something like 25,000 unique bacterial DNA strands in a gram of good aerobic, highly diverse plant organic matter compost. We don't even have names for well over 99% of these species. They are just numbers on the DNA sequence list. What does each species do? How do you culture them? Which ones are the ones that plant exudates feed?
Too many questions to begin talking about which ones are actually the important ones. To some extent, right now, we just have to let the plant do the choosing, because its exudates feed the beneficial organisms on the leaf, or root, surfaces.
We can assay for the beneficial bacteria and fungi we know about, but how much of the beneficial community do we know nothing about?
And yet, we are missing many of the beneficial species we do know about in our agricultural soils. Soil scientists often tell me that the bacteria and fungi just "return to the soil - rapidly". But they don't. The residues in soil, the continued plowing, the lack of organic matter in ag soil, all contribute to even the few beneficial species we know about not being in most ag soils.
We need to put them back. Compost and compost tea are excellent ways to do that. Commercial inocula of the beneficials are useful - inocula from companies like Helena Chemical Co, Organica Biotech Inc, Agri-Energy, EM, and so on. They all help.
Do we need to tip the ecology one way or another? Sure, but which way does addition of SO2 push you? Beneficial to the plants you want, or beneficial to weeds? We don't know. There's some work to do. We need to educate the public about the possibilities.
President, Soil Foodweb Inc.