Stratified network analysis of biochar-soil systems: Structural patterns associated with greenhouse gas emission responses

Biochar is extensively studied as a soil amendment with potential to reduce greenhouse gas (GHG) emissions, but field trial outcomes remain inconsistent, limiting generalisable mitigation strategies. Most analyses focus on direct amendment effects, offering limited insight into predictable co-variation patterns. This study applies stratified network analysis to 55 globally distributed field trials, examining chemical, microbial, and emission variables across environmental and management contexts. Correlation-based networks were constructed within ecological strata defined by climate, soil pH, crop type, fertilisation, and trial duration. Using multiscale metrics, such as edge density, centrality, modularity, assortativity, and canonical coherence, we evaluated association patterns at global (system), mesoscopic (subsystem), and variable (local) levels. Biochar application rate, soil pH, and total nitrogen consistently occupied central positions, influencing key structural associations within biochar-soil networks. CH₄, N₂O, and microbial gene markers were more peripheral, especially under acidic or low-input conditions, suggesting context-dependent patterns. Canonical correlation analyses revealed reproducible multiscale alignment (first-variate r = 0.9–0.95), supporting classification into meso-dominant, global-meso, meso-local, and disjoint regimes, each with distinct structural signatures. Partial-correlation networks retained key edges under 25% data removal, indicating structural consistency under data-limited conditions. The analysis is descriptive, but it identifies contexts where emission responses are embedded in a coherent multivariate scaffold and where interpretation is limited by sparse co-reporting. It supports prioritising soil pH, nitrogen context and amendment dose in monitoring and trial reporting, alongside more standardised co-measurement. Together, these results provide a practical basis for selecting core indicators and designing trials that test network structure across sites systematically. • Stratified networks summarise biochar-soil responses across 55 field trials worldwide. • Soil pH, nitrogen context and biochar rate are often central when retained in strata. • N 2 O and CH 4 responses and microbial gene markers shift in connectivity by stratum. • Threshold choice and regularised partial correlations show when associations persist. • Staged monitoring supported: emissions, soil pH, nitrogen status, and amendment dose.