Biochar from Agricultural Waste Enhances Rhizosphere Microbial Activity Over Bulk Soil

Abstract Understanding how biochar influences microbial processes in the rhizosphere compared to bulk soil remains limited. This study assessed the effects of biochars produced from different agricultural wastes at two pyrolysis temperatures on microbial properties in loamy-clay soil. Biochars were derived from vineyard prunings (VB), tomatoes (TB), cloves (CB), and bananas (BB) at 300 °C and 500 °C. A Completely Randomized Design (CRD) with five replications and nine treatments, including a control, was used. Soil samples were analyzed at harvest (8 weeks) for pH, electrical conductivity (EC), and microbial activities. Biochar significantly enhanced microbial activity, with stronger effects in the rhizosphere than in bulk soil. In the first growing period, biochar increased pH (by up to 1.2 units), EC (by 35%), alkaline phosphatase (by 42%), β-glucosidase (by 51%), denitrification (by 28%), and bacterial counts (by 63%) in the rhizosphere compared to bulk soil. In the second growing period, pH, urease, β-glucosidase, and bacterial counts remained higher in the rhizosphere, although denitrification declined by 19%. Among treatments, CB300, CB500, and BB500 significantly increased dehydrogenase activity (by 47%), while TB300 and CB300 promoted bacterial growth (by 58%) compared to the control. Biochar had a stronger impact on microbial activity in the rhizosphere than in bulk soil, with effects influenced by pyrolysis temperature and feedstock type. These findings highlight biochar’s potential to enhance soil microbial functions, providing insights for optimizing its application to improve soil health and crop productivity.