2013 ASHS Annual Conference

Vermicompost teas (VCT) are documented to increase plant growth and yield. However, the underlying mechanisms for these results remain obscure. Radioimmunoassay (RIA) was used to identify and quantify phytohormones present in commercially prepared “growth-promoting” VCT. Isopentenyladenine (IPA) and indole-3-acetic acid (IAA) were detected in different batches of VCT, along with a low amount of abscisic acid (ABA). Comparison of effects of VCT applied at the recommended rate with IPA and 6-benzyladenine applied at an amount equivalent to that supplied in the VCT treatment provided evidence that IPA increased Solanum lycopersicum vegetative biomass in the initial growth phase, but as the experiment progressed, results indicated that VCT improved the number of leaves, dry weight, and root length significantly over other treatments. The VCT also improved fruit number and fruit size significantly over control and other treatments. The results provided the first evidence that plant hormones are present in VCT, consistent with the growth promoting capacity of VCT. Two experiments provided evidence that different batches of VCT contained different amounts of phytohormones, including some growth promoting and growth inhibiting phytohormones, likely other hormones not analyzed, and other essential metabolites that had a greater beneficial effect on tomato plant growth and yield than equal amounts of isopentenyladenine. The study confirmed that phytohormones present in VCT play an important role, but there are other factors in VCT that contribute to increasing plant growth and yield. Although, VCT can be a good organic amendment, it is difficult to standardize the composition of VCT to ensure its quality due to the many variables involved in its production.