Understanding feedstock-dependent biochar performance beyond static material descriptors

Biochar is increasingly recognized as a multifunctional carbon material with important roles in soil improvement, environmental remediation, and carbon removal. However, its classification and evaluation commonly rely on static material descriptors, particularly the molar H/Corg ratio, to infer stability and long-term performance. While such descriptors provide useful information on aromaticity and intrinsic recalcitrance, they do not adequately capture how biochars derived from different feedstocks behave in real soil environments. Emerging evidence shows that feedstock identity governs functional performance through differences in labile carbon fractions, nutrient content, and interactions with native soil organic matter, including priming effects. In addition, biochar properties evolve through aging processes such as surface oxidation and functional group development, further influencing reactivity and stability. These dynamic responses mean that biochars meeting similar physicochemical thresholds cannot be assumed to be functionally equivalent materials. This perspective highlights an important dimension of biochar science that is not fully represented by descriptor-based approaches: feedstock-dependent and time-dependent performance in soil systems. Moving beyond static descriptors towards performance-oriented evaluation frameworks could strengthen the scientific basis for biochar assessment and support more function-specific design and application.