A high pH, low solubility of bound plant nutrients, and negative impacts on microbial communities are common drawbacks of biomass ash (BA) vermicomposting. In this study, nutrient-rich BA mixed with cow manure was tested at three different application rates to obtain final nitrogen (N), phosphorus (P), and potassium (K) contents of 3.5%, 7.0%, and 10.0% for bio-based fertilizers via vermicomposting. The results showed that all BA blends made with cow manure increased fermentation temperatures and allowed successful worm activity during the subsequent vermicomposting phase. The order of indicator enzyme activities in all vermicomposting samples was urease (220 μg NH₄ g⁻¹ h⁻¹) > β-glucosidase (95 μg PNP g⁻¹ h⁻¹) > alkaline phosphatase (91 μg PNP g⁻¹ h⁻¹) > arylsulfatase (83 μg PNP g⁻¹ h⁻¹) > acid phosphatase (60 μg PNP g⁻¹ h⁻¹). As an indicator of nutrient bioavailability, high correlations were observed between enzyme activities and microbial diversity in vermicompost samples. Determination coefficients (R²) obtained from multiple linear regressions between enzyme activities and bacterial population for T₀, T₁, T₂, and T₃ were determined as 0.90, 0.65, 0.73, and 0.90, respectively. According to a novel metagenome-based approach proposed within the scope of the present study, the stimulatory effects of Flavobacteriales, Burkholderiales, Saccharimonadales, and Pseudomonadales on enzyme activities for the nutrient solubility were found to be significant and positive. The findings of this study demonstrated that worm composting could be a sustainable bio-based technology for the production of slow-release fertilizer from nutrient-rich waste material.

Generation of the huge amount of bio-waste and their residues, including incineration ash, is a major technical and sustainability problem. To solve this problem, incorporating nutrient-rich residues into crop production has become an efficient practice to increase crop production. Vermicomposting of these wastes could be a viable option to manage both biowastes and their products in an environmentally friendly manner and close the material loop in bioenergy production. Therefore, the main objective of this study was to investigate the effect of vermicompost from biomass ash under hot and dry climatic conditions in summer on growth, yield and yield components of sweet sorghum (Sorghum bicolor var. saccharatum (L.) Mohlenbr). The high photosynthetic activity of sweet sorghum is important for biofuel production under conditions of high solar energy and water scarcity. This study provides a general overview of the feasibility of biomass ash vermicomposting processes and their potential use as a nutrient source for C4 sorghum under Bitlis ecological conditions of high solar potential and low water availability. Under Bitlis climatic conditions, the best yield was obtained when vermicompost was applied with a biomass ash content of 10.0% (T3). Plant height, plant weight, sugarcane and juice yields were reported as 133 cm, 146 g, 180 kg/da and 105 L/da, respectively.