Biochar and Crop Disease Resilience: Mechanistic Evidence, Context Dependence and Translation to Sustainable Management

Biochar is increasingly proposed as a soil amendment that can reduce crop disease while improving soil functioning and retaining carbon. Yet apparent disease suppression varies among feedstocks, pyrolysis conditions, application rates, soils, hosts and pathogens, and a favourable microbial response is not necessarily evidence of disease control. This critical narrative review evaluates the mechanistic and agronomic evidence linking biochar to crop disease resilience, with particular attention to Fusarium wilt and root rot, bacterial wilt, oomycete diseases, clubroot and foliar infections influenced by belowground treatments. Peer-reviewed experimental studies, mechanistic investigations, meta-analyses and authoritative reviews available through 2 September 2026 were considered through targeted scholarly searching and reference tracing. Three interacting routes emerge: changes in soil chemistry and physical habitat, reorganisation of rhizosphere communities and plant-mediated defence or stress responses. Evidence for microbial mediation is stronger when transplantation or biological intervention is used than when sequencing alone identifies correlated taxa. Tomato and pepper experiments offer compelling proof of principle, while research on sugarcane, tobacco and brassicas expands the range of relevant production systems but remains geographically and experimentally uneven. Dose responses can be non-linear, and high amendment rates, unsuitable biochars or co-applied amendments can obscure or reverse benefits. Carbon persistence, contaminant control and agronomic value must therefore be assessed alongside disease outcomes rather than treated as interchangeable gains. Biochar is best regarded as a potentially useful component of integrated disease management, not a universal curative material. Progress depends on characterising materials, including mechanism-discriminating controls, measuring pathogen load and economic outcomes, and testing durability across soils, seasons and crop genotypes.