Enrichment of Empty Oil Palm Fruit Bunch Biochar with Actinomycetes Bacteria as a Microbial Inoculant Carrier

Abstract

Background and Objective: Biochar is widely recognized for its porous structure, stability and large surface area, making it a promising carrier for beneficial soil microorganisms. However, limited information exists regarding its efficiency in supporting actinomycete enrichment at varying bacterial densities. This study addressed this gap by evaluating the colonization potential of biochar enriched with actinomycetes. The objective was to determine the optimal bacterial density and dilution level for maximizing colony formation under controlled laboratory conditions. Materials and Methods: The experiment was conducted from July to October 2024 at the Laboratory of Plant Biotechnology, Centre for Research Activities (CRA), Hasanuddin University, using a randomized group design with three replications. Actinomycetes were inoculated onto biochar at three bacterial densities (104, 108 and 1012 CFU/mL) and three dilution levels (10G5, 10G6 and 10G7). Colony observations were recorded weekly for four weeks. Visual colony morphology was documented and environmental conditions (pH, temperature and humidity) were monitored. Data were tabulated and analyzed using ANOVA and significant treatment effects (p<0.05 or p<0.01) were further compared using Tukey’s HSD test at " = 0.05. Results: Actinomycete isolates consistently exhibited round, raised colonies with irregular edges and smooth to wrinkled surfaces. The highest average colony count occurred at pH 7.93, 24.8EC and 66% humidity. The 108 CFU/g enrichment showed the greatest colony formation during the first week, reaching 4.5×109 CFU/g, significantly higher than the 104 and 1012 CFU/g treatments. Among dilution levels, 10G7 produced the highest colony count (4.5×109 CFU/g), showing a significant difference compared with 10G6 and 10G5. Conclusion: Biochar demonstrated strong potential as a suitable carrier medium for actinomycete enrichment, with the 108 CFU/g density and 10G7 dilution yielding optimal growth. These findings highlight biochar’s promise as an effective microbial inoculant for enhancing soil health and supporting sustainable agriculture. Further research should explore field-scale validation and long-term microbial stability.