Biochar–soil–tea nexus: a review of soil health, microbial interactions, and sustainable Camellia sinensis cultivation

Abstract Tea ( Camellia sinensis ) cultivation, central to global agriculture and livelihoods, is increasingly challenged by soil degradation, heavy metal contamination, and climate stressors largely driven by intensive practices. Because tea agroecosystems typically occupy acidic, nutrient-poor soils, sustainable management is essential. Biochar, a carbon (C)-rich product of biomass pyrolysis, has emerged as a promising amendment to restore soil health, mitigate contaminants, and strengthen crop resilience. This review synthesizes recent advances on the biochar–soil–tea nexus across five dimensions: (i) soil physicochemical and structural properties, (ii) microbial diversity and functions, (iii) nutrient mobilization and efficiency, (iv) tea productivity and quality, and (v) heavy-metal detoxification. Evidence from field and controlled studies shows that biochar can buffer soil acidity, enhance nutrient retention, restructure microbial communities, reduce pollutant bioavailability, and improve tea growth and quality. In addition, it offers a practice guide for tailoring biochar application based on feedstock and pyrolysis conditions to achieve specific soil and plant health goals. Furthermore, biochar contributes to C sequestration and greenhouse gas mitigation, situating its use within the broader framework of climate-smart agriculture. Despite these benefits, outcomes are highly context-dependent, shaped by feedstock type, pyrolysis conditions, soil characteristics, and application rate. Critical research gaps remain, including scarce tropical field studies, limited long-term field evaluations, inconsistent biochar characterization, and insufficient understanding of cultivar-specific and microbial interactions. By mapping these uncertainties and outlining research priorities, this review provides a foundation for optimizing biochar use in tea systems and guiding region-specific strategies for sustainable cultivation in a changing climate.