C. 4. How to tell a "good" tea

Soil Foodweb Inc performed a study of how do you know if compost tea will “work”?

The results (given below in Table 1). clearly show that plate counts are inappropriate for determining whether a compost tea will protect plant surfaces from disease. Direct determinations were excellent means of showing that tea can protect leaf surfaces from disease causing organisms.

Methods

Plants were obtained from a greenhouse where blight was causing a severe problem. All plants used were just beginning to show “burn” on the leaves from the disease.

Five of the plants were sprayed with Tea One, five plants sprayed with Tea Two. Control plants (water alone) and fungicide treated plants died within a week, as did the plants to which tea one (tea lacking suppressiveness, see table below) was applied.

Does the fact that plants sprayed with Compost Tea One died mean that compost tea does not work? No, because the plants sprayed with compost Tea Two (tea capable of suppressing disease in the table below) survived and grew well.

What was the difference in the teas? Tea Two, designated tea capable of suppressing disease in the tbale below, had high levels of active and total fungi, active and total bacteria, and good protozoan numbers. Application of these organisms to the plant foliage resulted in excellent coverage of the leaf surfaces. All of these plants lived.

Tea Two, designated tea lacking suppressiveness, did not contain adequate fungi, or fungal activity, and lacked the protozoa needed. While exactly the same amount of tea (or water, or fungicide on the control and fungicide-treated plants) was sprayed on all plants, Tea One did not have an adequate microbial population to protect the plant surface.

Plate methods could not differentiate between the two teas.

TSA incubated at room temperature, in aerobic conditions, measures “aerobic heterotrophs”. There was no detectable difference between the two teas using plate methods, despite the fact that Tea Two was capable of suppressing blight, while Tea One, sprayed at the same concentration, in the same conditions, did not suppress disease.

King’s B medium selects for pseudomonads, but not all these bacterial species are beneficial to plants. Enumeration indicated that there were more pseudomonads in the not-suppressive tea. Plate methods cannot distinguish whether the bacteria growing on this plate, and thus presumably pseudomonads, will be beneficial to the plant. If these values were used to measure “species richness-diversity”, the not-suppressive tea would get a higher “index” score than the tea that resulted in the plants remaining alive and producing a bumper crop of tomato later in the year.

Please note that “species richness-diversity” is not a valid name for any ecologically accepted measure of diversity. The lab that developed and uses this index will NOT explain how this index is calculated, and will not show any data that documents what relationship the index has with plant health. They claim the index is in any introductory textbook, but in fact, no textbook anywhere has a measure called species richness-diversity. Until such time as the lab using this index documents the claim that a higher index value actually means a benefit to the plant, the use of this index must remain highly questionable.

Spore-formers are determined by boiling the material in question to kill vegetative cells, followed by plating the material on TSA. Only spores or highly dormant stages of organisms survive boiling. Those spores capable of growing on TSA, at room temperature, in the particular oxygen conditions present in the plate (please recognize that oxygen exchange is reduced by the fact that the plates are covered), are then enumerated. Again, the not-suppressive tea had higher plate enumeration values. What is the relationship between what will grow on a plate, and physiological functions occurring in the soil, or on plant surfaces? These data show that there is no relationship.

Direct determinations separate bacteria from fungi. Plate media do not separate even bacteria from fungi, much less not giving an indication of what is going on with approximately 99.9% of the species present in the material plated.

Direct determinations also let you know whether protozoa or nematodes are present and performing their functions. A much clearer picture of what biology is present and performing their functions is possible when using direct determinations. Direct methods let you know if coverage on leaf surfaces is adequate. These types of assessments need to have a clear relation back to benefit to the plant.

Please note that there is no consistent relationship between plate count enumerations of “species richness-diversity” and improvement in plant growth. Plate counts do not assess diversity or activity of the organisms in the test material. An insignificant number of the actual total individuals or total species present in a sample grow on any single plate medium or set of lab conditions that it is difficult to see why anyone would continue to pretend that there is a relationship between plant growth and plate count assessments of diversity.

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