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

Authors: JAVANMARDI, JAMAL - Shiraz University; DOS SANTOS, MARCIA - Universidad De Sao Paulo; Manter, Daniel; VIVANCO, JORGE - Colorado State University

Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/30/2023
Publication Date: 1/17/2024
Citation: Javanmardi, J., Dos Santos, M.L., Manter, D.K., Vivanco, J.M. 2024. Worm compost tea's plant growth-promoting power: Is it the microorganisms or chemical properties? Journal of Plant Nutrition. 47(4):583-594. https://doi.org/10.1080/01904167.2023.2280133.
DOI: https://doi.org/10.1080/01904167.2023.2280133

Interpretive Summary: Tomato seedlings (Solanum lycopersicum cv. Rutgers) and three basil (Ocimum basilicum) cultivars were treated with vermicompost tea (VCT), autoclaved vermicompost tea (AVCT), or a control (water) for 3 times during 7 weeks of the experiment period to determine if the effects of this biological fertilizer on plant growth are due to the presence of microorganisms or chemical nutrients. 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. Application of vermicompost tea as an alternative to its direct mixing with soil provides easier application and lower costs. The major benefits of vermicompost tea on plant growth appear to be related to its chemical composition and its resultant fertilizer (e.g., nutrients and/or microbial-derived compounds) effect. Autoclaving appears to increase the fertilizer effect of vermicompost teas, which may have benefits for increased shelf life and easier storage of teas. It seems that autoclaving of vermicompost tea is practically beneficial for those hydroponic systems that would like to use the advantages of biofertilizers without the hassle of technical system clogging due to microbial activity. However, for basil it was shown that the genotypes responded differently to VCT and AVCT probably due to the specific biochemistry and physiology of these genotypes. We must caution that the autoclaving of vermicompost teas may not be advisable when part of the management objective is to use these teas to introduce living microbes into a system, e.g., to introduce biocontrol organisms into soils where pest and disease are typical problems.

Technical Abstract: Tomato seedlings (Solanum lycopersicum cv. Rutgers) and three basil (Ocimum basilicum) cultivars were treated with vermicompost tea (VCT), autoclaved vermicompost tea (AVCT), or a control (water) for 3 times during 7 weeks of the experiment period to determine if the effects of this biological fertilizer on plant growth are due to the presence of microorganisms or chemical nutrients. 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 significantly increased pH and plant available minerals including NH4+, NO3-, K, Mg, Zn, Fe and Mn. A 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, it appears that the major benefits of vermicompost tea do not necessarily require living organisms as both treatments (VCT and AVCT) significantly increased plant biomass. Furthermore, the AVCT treatment had a significantly greater impact on plant biomass. Thus, the growth promoting potential of vermicompost tea may not be associated with microbial biomass per se but rather, the release of extracellular microbial signals/nutrients and/or the nutrient availability of the applied vermicompost tea. The most applicable benefit of autoclaving VCT is for increased shelf life as well as for hydroponic systems that would like to use the advantages of biofertilizers without the hassle of technical system clogging due to microbial activity.