Biochar‐based fertilizers in agriculture: A global systematic review with a focus on cotton cropping systems and implications for West Africa

Biochar‐based fertilizers (BBFs) or enriched biochar, produced by combining biochar with mineral or organic fertilizers or additives, offer a promising solution to improving soil fertility and crop productivity while reducing chemical fertilizer dependency. However, their effects remain highly variable across studies, depending on soil types, crops, species, management practices, and biophysical conditions. This systematic review, conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses framework, synthesizes global BBFs evidence from general agronomic to cotton‐specific outcomes, assessing their relevance for West African agroecosystems. A total of 820 studies were retrieved from searches conducted in the Google Scholar search engine and Dimensions and Scopus databases, without time restrictions, and were guided by the Population, Intervention, Comparator, Outcome framework. Research interest in BBFs has increased sharply, with 74% published between 2021 and 2024. Globally, BBFs were predominantly evaluated under experimental conditions (50% of cases), and 61% of the biochar feedstocks originated from cotton residues. The enrichment type, soil texture, applied doses, and climatic zone significantly influenced the effectiveness of enriched biochar, reflecting methodological heterogeneity. Under humid subtropical conditions and moderate application rates, BBFs generally improved soil physicochemical properties, whereas responses in arid and Mediterranean regions were more variable and sometimes negative at high rates. In cotton cropping systems, BBFs application consistently improved vegetative growth and physiological performance, though yield responses were mixed: positive effects on reproductive components were reported in some studies but remained weak or nonsignificant in others. Overall, BBFs can support sustainable soil and nutrient management under specific conditions, but outcomes remain strongly context‐dependent across diverse agricultural systems.