SAFETY AND EFFICACY OF COMPOST TEAS ANALYZED IN RECENT STUDIES

The Winter 2004-2005 issue of OMRI Update, published by the Organic Materials Review Institute of Eugene, Oregon, features two recent studies on compost teas which point out the different impacts of brewing methods and additives. In one study by Will Brinton and colleagues at Woods End Laboratory, published in the Journal of BioDynanties, the researchers look at the capacity of types of compost tea to sustain a population of E. coli. They recommend that compost tea practitioners pay attention to avoiding fecal contamination during the production of the teas. Their results highlight no obvious advantage of aerated systems over traditional methods. Two differing types of aerated commercial brewers were used, along with a traditional European method of brewing compost tea in a loosely covered vat and stirred once a day.

In the second study by Steven Scheurell and Walter Mahaffee, published in Phytopathology, the abilities of aerated and nonaerated composted teas to control the fungal disease, Pythium ultimum, were tested. They conclude that only aerated compost teas with specific nutrient additives deliver consistent results. Their work also suggests that residual nutrients in the teas, from molasses for instance, do not contribute to the teas' disease suppression effects.

Their methods included use of two commercial composts and one vermicompost product. The aerated compost tea was produced using a commercial brewer. Finished teas were tested for levels of bacterial and fungal communities using three common methods of counting these organisms.

The commercial aerated system produced consistent results when brewed with kelp, humic acids, and glacial rock dust. These results were similar for all three compost types. The research team found the nonaerated tea to have a limited suppressive effect on the disease, but found some practical drawbacks, such as bad smell and long production time, as reasons against using this method.