Fly ash amended vermicompost as a growing medium for tomato (Solanum lycopersicum) and Swiss chard (Beta vulgaris): implications on growth and heavy metal uptake

Our study evaluated the potential use of fly ash amended cow dung based vermicompost as a medium for Swiss chard and tomato growth, yield, and heavy metal uptake. Fly ash vermicompost was used to substitute 50%, 25%, and 0% cocopeat with the application of 100% and 50% of the recommended hydroponic fertilizer. The vermicompost incorporation level (VC) and fertilizer level (F) did not significantly influence Swiss chard chlorophyll content, but significantly influenced that of tomatoes. The highest chlorophyll content in tomatoes was recorded under the 25%VC with 100% F. For Swiss chard and tomato, the incorporation of 50% fertilizer resulted in an average decrease in yield of 43.8% and 15.02%, respectively. Interestingly, with tomatoes, the highest yield was observed under 50% VC with 100% fertilizer treatment, which was 10.3% higher than that of the control. VC did not significantly influence the Zn concentration for either crop, with none of the treatments showing a Zn concentration above the maximum permissible limit for vegetables at 60 mg/kg. For both Zn and Cr, 50% fertilizer application resulted in the highest concentrations in both crops. Notably, the Cr concentration which has a maximum permissible value of 2.3 mg/kg resulted in all treatments, including the control, yielding values above this critical value. Based on our study, Swiss chard and tomatoes grown with 25% fly ash amended VC may be consumed with limited human risk, though fly ash vermicompost alone does not seem to have enough nutrients for tomato and Swiss chard growth and require fertilizer supplementation.