Compost Tea - Promises and Practicalities

Most of us have heard about the excellent results achieved with compost teas, but how do they work?

There are two main ways.

1. Compost tea contains a set of aerobic organisms that perform a variety of beneficial functions:

• They consume the foods that plants put out around their bodies. Plant exudates, both from roots and leaves, enhance the disease-suppressive bacteria and fungi that occur in aerobic tea, leaving no food for disease-causing organisms. If pesticides and inorganic fertilizers have killed the beneficial bacteria and fungi that plants “expect” to be present around their roots, those exudates will be used, eventually, by disease-causing organisms. Disease is then rampant and hard to control. • They occupy the infection sites, so even if the disease-causing organisms do start to grow, they can’t penetrate into the tissues of the plant. • They occupy the space around the plant, leaving no room for the disease organisms to exist. • They consume disease-causing organisms. • They produce compounds that inhibit the growth of disease-causing organisms.

2. Compost tea contains soluble nutrients that perform two key functions: • They feed the organisms already within the tea, so they grow faster, are healthier, and can perform their disease suppressive functions faster. • They feed the plant, making it healthier and able to make more food to feed the “good guys” that suppress disease-causing organisms. In addition to suppressing disease, the organisms in tea confer other crucial benefits on plants: • They retain nutrients in the soil around the plants, so additional fertilizer will not be needed. This has an additional economic benefit, because if nutrients are kept in bacterial and fungal bodies and therefore stay in the soil instead of leaching into your drinking water, your water bill goes down. Your city doesn’t have to spend so much money cleaning those nutrients out of the surface waters you want to drink. • They make nutrients available to plants at the rates plants require. Reduced fertilizer applications almost always occur if you have a healthy soil with the right sets of organisms for your plants. • They detoxify the soil and water, making it easier for plants to grow. If anaerobic conditions exist in the soil, the aerobic organisms have to use those anaerobic materials first, before they get to your plant. • They build soil structure, so air and water can easily reach your plant’s roots, keeping the soil well aerated and holding water in tiny “swimming pools” in the soil. The result is healthier plants, with roots that go deeper and don’t require constant watering.

It’s amazing what helping out the creatures in your soil can do! So, why doesn’t your soil already have these organisms? They certainly were there, but over the years, the things we have done to soil have killed the beneficial organisms. Every pesticide kills something beneficial in the soil. High rates of fertilizers kill beneficial soil life, too, through simple osmotic shock. Air pollution takes its toll on the organisms on the foliage, and dust, UV and pesticide drift kill your beneficials, even if you don’t use those chemicals yourself. It’s time to think about getting those good guys back with your plants!

COMPOST TEA: INGREDIENTS 1. Compost. Not putrefying organic matter. Please, get this one straight. It’s critical. Compost is aerobic. Consider what that means — it means that compost does not stink. Only if it hasn’t been properly aerated will it smell bad. If it smells like sewage, that means it is sewage, not compost. If it smells like manure, it is manure. Trust your nose, not someone who is trying to sell you something. If it smells bad, there’s something wrong with the compost, and you should get the health authorities to deal with the situation. Real, aerobic compost contains a huge diversity of bacteria, fungi, protozoa, nematodes and perhaps even microarthropods. Beneficial species are almost always strictly aerobic, which means those conditions in which stink starts to occur are killing the “good guys” and helping out the “bad guys,” which will also attack your plant roots, foliage and seeds.

2. Water. Consider your water source carefully. Why do we put chlorine in water? To kill human pathogens, right? Will the chlorine kill the compost tea organisms? Absolutely. Therefore, you must de-gas the chlorine by aerating the water, or adding citric acid (yes, even the breakfast drink Tang has a high enough concentration of citric acid to work). Check pH and hardness if you take your water from a well — pH levels that are too high or too low can cause problems.

3. Food. To grow beneficial bacteria and fungi in the tea during the tea-making cycle, in general you will want to maximize fungal biomass to the greatest extent. The bacteria will be in the tea as long as you use good compost, a bit of molasses or other complex sugar. If you need fungi — and most agricultural soils desperately need fungi, which is also lacking in most foliar applications — then you need to add kelp, rock dust, and fish hydroysates or humic acids. You probably want to try a combination of the fungal foods to see what works best. Be aware that many of the compost tea-maker companies are working on the question of how to improve the fungi.

We were recently testing a variety of teas and found that about 85 percent of the suppressiveness of a tea comes from bacterial coverage. If about 65 to 70 percent of your leaf surface is covered with bacteria — which translates into at least 300 micrograms of bacteria per milliliter of the tea, applied at about five gallons of tea to the acre — then you will have little to no disease 85 percent of the time, under most conditions.

However, when disease conditions are perfect for the growth of disease-causing organisms, then you better have that last 15 percent of the leaf covered with fungi. Aerobic fungal species are the ones that can take on the worst fungal bad guys and win. In a “no-disease” year, no worries, almost any tea will be OK. But in a tough situation, it is extremely important to have the fungal component in the tea. That translates into about two to 20 milligrams of fungal biomass in a tea, so that the leaves will be adequately covered when applying at five gallons of tea per acre. What about soil? Again, bacteria and fungi are needed, but protozoa and nematodes are also needed. Almost any machine provides good bacteria, given good compost and molasses or other sugar, but at least some active fungal biomass has to be present to get fungi into the soil to compete with the bad guys and help open up soil structure. No fungi, no macroaggregates, no passageways for air or water to move into the soil.

4. Plant Food. As long as the plant is being sprayed, do some foliar feeding. Getting the leaf surface completely covered is important here, too, because bacteria and fungi respire carbon dioxide, which elevates CO2 in the atmosphere surrounding the leaf surface, causing the stomates to open more rapidly, for a longer time — thus, the plant takes in more of the foliar nutrients applied in the tea.

For more details on Compost Tea-making equipment as well as how to test your tea please refer to the original article at http://www.acresusa.com/toolbox/reprints/Dec03_Compost%20Teas.pdf

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Reprinted from December 2003 • Vol. 33, No. 12