Biochar for Sustainable Agriculture: A Systematic Review and Conceptual Framework Linking Biomass Type and Pyrolysis Conditions to Soil Macronutrient Dynamics

Sustainable soil fertility management requires amendments that improve nutrient retention while supporting nutrient recycling. This review synthesizes current evidence on how biomass type and pyrolysis conditions determine biochar properties and, consequently, the dynamics of N, P, K, S, Ca, and Mg in soils. The analysis integrates bibliometric screening, comparative data on feedstock groups, and mechanistic evidence on adsorption–desorption, ion exchange, precipitation, microbial transformations, aging, and nutrient release. Feedstocks were grouped into agricultural, woody, animal, urban, and aquatic biomasses, whose mineral composition and structural features produced contrasting nutrient-source potentials. Across the biochars reviewed, pyrolysis temperatures ranged from 200 to 900 °C, generating materials with pH values of 4.7–13.7, surface areas of 0.18–545.66 m2 g−1, and nutrient contents of 0.04–8.22% N, 0.02–5.30% P, and 0.15–7.01% K. Higher pyrolysis temperatures generally increased aromaticity, alkalinity, porosity, and mineral concentration, whereas mineral-rich feedstocks provided greater direct nutrient and base-cation inputs. This review shows that BC functionality is context-dependent and should be matched to soil nutrient limitations, pH, texture, and crop requirements to improve nutrient-use efficiency and support sustainable agriculture.