What's 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Outdated methods of assessing numbers of organisms in samples might lead you to believe compost tea doesn’t have much diversity.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.
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.
