BOOK OF ABSTRACTS 221 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Hall A Poster Session / Environment, Agriculture, and Forestry P4.5 PGPR-Inoculated Biochar as a Soil Amendment Petr Haleš1, Martin Súkeník1, Barbora Hlaváčková1, Michal Kalina1 1 Brno University of Technology, Faculty of Chemistry, Purkyňova 464/118, 612 00 Brno, Czech Republic, petr.hales@vutbr.cz Biochar is an important soil conditioner in agriculture, serving as a long-term source of organic matter and a short-term source of minerals. However, due to the high temperatures used during its production by pyrolysis, a non-living porous matrix is often formed, which limits its direct impact on biological processes in the soil [1]. Enriching biochar with plant growth-promoting rhizobacteria (PGPR) therefore offers a way to utilize its physicochemical and structural properties for microbial colonization and to supplement this soil conditioner with a living microbial component [2]. Four types of commercial biochar samples (Carbohran, Novocarbo, Sonnenerde, and Zera) produced from various biomass feedstocks at different pyrolysis temperatures and the bacterial strain Azotobacter vinelandii CCM 289 were used in this study. In the introductory section, the biochars were characterized using thermogravimetric analysis (TGA), and the physicochemical properties of aqueous extracts (pH, conductivity) and their elemental composition were determined using ICP-OES. Prior to colonization, the effects of pH, ionic strength, and biochar extract on bacterial growth and its capability to colonize biochar structure were simulated in preliminary cultivation experiments. The aim was to assess separately the influence of these parameters on cell viability and concentration and the capability of bacteria to produce alginate extracellularly. These bacterial suspensions were cross-linked with a 2 wt.% CaCl2 solution into the alginate hydrogel, which was characterized using rheometry. Subsequently, two colonization methods were compared: post-cultivation (mixing the prepared bacterial suspension with biochar) and co-cultivation (direct bacterial growth in a biochar suspension). For both approaches, the effect of biochar presence on cell concentration and viability was evaluated using flow cytometry, and the viscoelastic properties of the resulting alginate hydrogels with entrapped bacteria were monitored using rheometry. These prepared systems were freeze-dried to ensure stability for subsequent soil applications. The core of the work consisted of a 92-day cultivation experiment with the presence of a model plant - maize (Zea mays) under controlled conditions (temperature, moisture, irrigation, illumination). The post-cultivation colonization method was chosen for
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