Compost tea is a liquid extract of compost produced by steeping finished compost in water in order to extract beneficial microorganisms and compounds. The theory is that we can add precisely what a soil is lacking with compost tea and it is supposed to be a speedy, cost-effective way of improving soil health and plant growth. To test this theory, Jim Tarnowski and group of farmers in Indiana ran a SARE supported study on their operations. In the first article in this series, Jim described the process and that they saw no improvements from the compost tea treatment. Here’s what Jim says about what the study revealed and his recommendations for others about using compost tea.
Benefits of Doing the Study
The soil food web analysis helped to validate our good soil practices and this was a benefit. Also, the observation of the earthworm counts, water infiltration rate, compaction testing, and other soil health tests were valuable for raising our awareness. The study reinforced that living plants in the soil at all times is very important. For some of us, we came full circle back to our original intuitions about soil and Mother Nature. Using our own native understandings of our soil and the ecology of the farms we inhabit we feel better equipped with knowledge and awareness to continue using good soil building practices and our own observations.
One of us was already purchasing microbes to apply to the soil and was glad to learn how to brew compost tea in place of the purchased microbes. Learning how to accurately calibrate a sprayer and apply the tea at recommended rates was also something most of us learned.
We learned a lot from one another in this study. The interchange of problems and solution, and different approaches informed each one of us in how we approach our own land. Many of us have discontinued tilling the fields and gardens form the knowledge we gained out of this study.
Benefits to Other Vegetation from Compost Tea
Outside of the study plots a few of us were applying much higher rates of compost tea to other plants and did see noticeable benefits. In one case, fire-blight problems in an orchard were brought under control with the use of foliar spraying. In another case, tomato starts were watered with compost tea and other were not. The compost tea fed tomatoes were much healthier and larger. It may be that we need to apply a much higher per acre rate of the compost tea to see soil benefits. Some of us feel there may be usefulness of the compost tea for foliar feeding and disease protection, but doubtful about its usefulness as a soil application.
Compost Tea Disadvantages
Disadvantages of the compost tea brewing are that it is expensive, takes considerable time and knowledge to brew decent teas, cleaning the brewer is a pain, and often the brew overflows or the equipment malfunctions. Tea brewing required a lot of baby sitting for the 24 hours it is brewing. Brewing the tea is more of an art than a science. The learning curve is very steep.
Furthermore, in order to apply the tea, we had to make trial and error adjustments to spraying equipment, and had many problems with clogging of screens and filters. Great care has to be taken to get the tea with living organisms applied. The tea needs to be applied during cooler periods of morning or evening in summer, and just previous to rainfall. Another disadvantage in terms of soil health is that a tractor and sprayer must be driven over the field for each application and this adds to compaction of the soil.
Although the soil food web analyses are insightful, they are also very expensive – over $200 per test. This is prohibitively costly for anyone on a farm scale.
What Do Others Say About Compost Tea Success?
In speaking with soil microbiology researchers, Rodale farms, and others around the county investigating compost tea using scientific methods, none of them have found any clear benefits from soil or foliar uses. Some results have even showed negative impacts on plants. This is perplexing given the exponential growth in compost tea use around the country, the number of companies selling compost tea makers and equipment, and the increasing number of expert speakers on the benefits of compost tea at national organic tea among soil ecologists researching the soil food web. There is clear evidence that the biodiversity of organisms in the soil is critical for full soil function and health, but so far no one has corroborated that the use of compost tea is effective in aiding the soil. Some of us find it troubling that the leading researcher and proponent of compost tea in the world has not published any peer reviewed and scientifically verified data supporting the claims that compost tea is effective. Some of us feel this begs the question: Is compost tea a magic elixir or simply snake oil? A lot of money is being made in the compost tea industry today.
Our Recommendations to Fellow Farmers and Ranchers
Unfortunately our results show there were no effects on soil health due to the compost tea treatments. Therefore we feel there may be a negative economic impact because brewing and applying compost tea was expensive and very time consuming.
We did find that our other soil health practices of reducing or eliminating tillage and artificial fertilizers and pesticides, while increasing cover cropping have been the most likely reason for improved soil. In some cases there were significant changes in soil health in just the short time period of two years. There are of course many other studies and practical observations from farmers and ranchers showing these conservation practices to be of benefit. This study did raise our awareness of the complexity and great value of healthy soil, so this directly impacts the environment on our farms. We feel there were beneficial social impacts from the two years of getting to know each other, our unique approaches and knowledge of soil practices that we exchanged with each other.
In conclusion we would advise other producers to trust in their own native soil observations and their intuitions about soil health. Rely on the tried and true methods of building soil health including: greatly reduce or eliminate tillage, especially deep tillage, eliminate pesticide use and salt-based fertilizer use. Employ the use of diverse cover cropping systems such that you always have a living crop in the soil. Use diverse crop rotations, and have animals as part of the system. Get to know other producers in you area or region who are trying to improve soil health and exchange knowledge with them.
We also advise producers to thoroughly investigate compost tea before investing money and time in this process. We advise this because we can find no credible scientific verification for the benefits of compost tea, and our own study found no impact on the soil health from the use of the compost tea. A further step with investigating compost tea will be to observe results form using various application rates of much greater quantities than we did in our study.