<p>This study investigated the effect of a low-rank coal-derived soil amendment, produced through microbial digestion of lignite, on the growth of sweet pepper (<i>Capsicum annuum</i>), rhizosphere microbial communities, and soil physicochemical properties.&#xa0;Greenhouse pot experiments were conducted using two application rates of the coal-based amendment (0.4% and 1.5% w/w), alongside treatments with a commercial organic fertilizer, raw lignite, and untreated control. Physical, chemical soil properties and the rhizosphere microbial communities were analyzed.&#xa0;The coal-derived amendment significantly increased pepper fruit yield by 70–90% compared to the control. Commercial organic fertilizer amendments primarily enhanced shoot biomass with minimal effects on root development, while the coal-derived amendment promoted robust root growth, including greater total biomass, leaf surface area, and fine-root density. In contrast, raw lignite amendments had negligible impact, emphasizing the role of microbial processing in releasing the constituents and unlocking the agronomic potential of lignite. Soil analyses indicated that the coal-derived amendment increased soil organic matter content without corresponding increases in nitrogen or phosphorus levels, suggesting its effects are not driven by direct nutrient input. Rhizosphere community assessments demonstrated distinct microbial shifts, including the enrichment of <i>Acidobacteriota</i>,<i> Chloroflexi</i>, and <i>Ascomycota</i>, taxa associated with organic matter turnover, nutrient mobilization, and plant growth promotion.&#xa0;The results support the use of this coal-derived amendment as a scalable, sustainable alternative to conventional fertilizers, promoting crop productivity and soil health via root system enhancement and beneficial microbial modulation rather than through nutrient supplementation.</p>