A Correlation-Based Approach for Predicting Humic Substance Bioactivity from Direct Compost Characterization

The efficient characterization of compost quality is essential for optimizing its application in agriculture and soil improvement. In this study, a correlation-based approach was employed to evaluate relationships between physicochemical properties, structural features, and reactivity indicators of compost extracts-fulvic acid-like (FA-L), humic acid-like (HA-L), and dissolved organic matter (DOM)-and their respective bulk composts. The goal was to identify key compost parameters that can serve as reliable predictors of humic substance composition and bioactivity, thereby reducing reliance on labor-intensive humic substance extractions. A comprehensive set of elemental, spectroscopic (UV-vis, ATR-FTIR, ¹H-NMR), and thermal (TGA-DSC) analyses were conducted to assess the composition and stability of the extracts. Strong correlations were found between compost oxidation state (<i>C_oxi</i>/<i>C</i>), cation exchange capacity (<i>CEC</i>), thermal stability, and the structural characteristics of humic substances-like (HS-L) fractions, suggesting that direct compost characterization can effectively predict humic substance reactivity and agronomic potential. The findings also align with a previously developed Compost Quality Index (CQI), reinforcing the functional role of humic substances in soil fertility and nutrient retention. By establishing a simplified yet robust compost assessment framework, this study advances the potential for efficient, cost-effective evaluation methodologies for compost quality.