Woods End has been active in the field since the late 1980′s and has worked closely with Friedrich-Wilhelm University Bonn (Dr. Tränkner) on compost tea efficacy studies.
Early enthusiasm and some misinformation has resulted in compost tea methods being promulgated where sugar-type materials and other “adjuvants” are added to “boost” or “brew” microbe populations. This not only alters the natural bio diversity of the compost extracts but significantly increases the risk of potentially pathogenic E. coli growing.
European research has shown that one good reason to consider addition of a microbial growth additive during the extraction process is be to support the survival of bacteria on the phyllosphere of the plant, where active suppression may take place. CASO and rapeseed oil extracts are such additives.
CAUTION ABOUT COMPOST TEAS: Important Laboratory studies on tea hygiene have indicated that teas can support E. coli growth if the compost is immature or if sufficient readily available carbohydrates (such as sugars or fresh plant extracts) are added during the tea process. In other words, testing teas for maturity and bacterial populations is a good way to select a product. (See Woods End and JPF paper at bottom of this page).
The primary objective therefore in analyzing compost extracts for microbiological parameters is to demonstrate:
- Absence of pathogens (E. coli) in the tea,
- Lack of toxicity to microbe and plants, and
- Presence of microbes known to confer disease resistance to plants.
Other factors that may be tested, but for which limited scientific data are available, include: total bacterial and fungal counts, ratios of organisms and aerobic:anaerobic relationships.
However, it is not known whether or to what extent these microbiological parameters are relevant to the use of the teas. Manufacturers should be aware of the USDA Compost Tea Task Force report on compost tea hygiene. The Woods End on-line news page contains some stories related to compost teas. In addition, if teas are being used to provide nutrients, then other analyses may be useful (see section on compost testing). There is very little information that documents the usefulness of teas to provide nutrients.
- ACTIVE AEROBIC BACTERIA – Also called Aerobic or Heterotrophic Plate Count, the test measures the total number of oxygen-utilizing bacteria per gram of compost or milliliter of tea. Greater than 100 million per gram or ml are desirable in properly mature compost tea.
- TOXICITY TEST- Using a highly sensitive toxicity-indicator plant, the occurrence of toxins such as herbicides is ranked.
- VIABLE BACTERIAL SPORES -This facet of the bacterial population indicates the presence of several Bacillus species having the ability to suppress certain fungi responsible for plant disease. A gram of healthy compost should contain about a million of these bacteria.
- ACTIVE FUNGI- Actual growing fungi in amounts between 1,000 – 10,000/g or ml of compost or tea contribute disease resistance to certain crops and indicate overall tea health.
- FLOURESCENT PSEUDOMONADS -These bacteria impart fungi-disease resistance to plants. Approximately 1,000 to 1 million/g of compost or ml of tea are desirable.