Worm compost tea’s plant growth-promoting power: is it the microorganisms or chemical properties?

Abstract

Vermicompost tea (VCT), an eco-friendly biofertilizer, is becoming increasingly popular due to its notable benefits on plant and soil health. However, the reasons behind its efficacy, whether due to growth regulators, minerals, microorganisms, or their combination, remain ambiguous. Seedlings of tomato (Solanum lycopersicum cv. Rutgers) were treated with VCT, autoclaved VCT (AVCT), or water (control) for three times over 7 weeks to determine if the effects of this biological fertilizer on plant growth are due to the presence of microorganisms or chemical nutrients. A significant increase was observed in plant growth with either the VCT or AVCT treatments compared to the control, while for most measures, plant growth was higher in the AVCT versus the VCT treatment. Autoclaving VCT increased pH and plant-available minerals, including NH4 +, NO3 −, K, Mg, Zn, Fe, and Mn. Metagenomic analysis of bacterial specimens in VCT revealed the most abundant genera as Novosphingobium, Sphingobium, Luteimonas, Pseudomonas, Planctomyces, Rhodoplanes, Mycoplana, Bacillus, Achromobacter, and Devosia. Although many of these genera contain known plant-growth-promoting bacteria, the major benefits of VCT do not necessarily require living organisms as both VCT and AVCT increased plant biomass. Thus, the growth-promoting potential of VCT may not be associated with microbial biomass by itself but rather with the release of extracellular microbial signals/nutrients and/or the nutrient availability of the applied VCT. The advantages of autoclaving VCT are the increased shelf life and the potential use of biofertilizers within organic hydroponic systems without technical challenges due to clogging from microbial activity.