Chemical and molecular profiling of dissolved organic matter within varied compost: a comprehensive spectroscopic study

Abstract

Abstract Limited information is available regarding the chemical and molecular compositions and structures of dissolved organic matter (DOM) originating from diverse matured composts. In this study, the compost DOM extracted from composts of chicken manure co-composted with wheat straw (WS), rice husk (RH), and Chinese herbal residue (HR) underwent comprehensive characterization using UV-vis absorption, excitation-emission matrix fluorescence coupled with regional integration analysis (EEM-FRI), high-performance size exclusion chromatography (HPSEC), fourier-transform infrared (FTIR) spectroscopy. The results, as evidenced by the SUVA254, E2/E3, and SR values, consistently revealed a decreasing trend in aromatization and polymerization degree in the order of WS > RH > HR DOM. EEM-FRI analysis indicated that both WS and RH DOM composed of more humic-like substances (Region III+V, 45.4-51.1%) than HR DOM (37.9%), while the latter one enriched more protein-like substances (Region I+II, 48.3%). This implied that WS and RH DOM exhibited a more pronounced humification degree, which is supported by observation reflected by the humification Index (HIX) values. HPSEC revealed broad molecular weight (MW) distributions encompassing a range of 0.1 to 300 kDa across the three compost DOM. As comparison, the Mw and Mn followed the order of WS> RH > HR DOM, signifying a progressive reduction in MW amongst the distinct compost DOM. FTIR spectra suggested that three compost DOM predominantly composed of intricate mixtures of aromatic and aliphatic species, along with O-containing functional groups (e.g., hydroxyl, carboxyl, and carbonyl). Notably, WS and HR DOM exhibited an elevated presence of aromatic and aliphatic groups, whereas RH DOM presented an increased abundance of polar O-containing structures. In summary, this study has pointed out that diverse compost DOM manifest distinct chemical and molecular characteristics. These findings offer a foundational framework for assessing compost maturity and for the judicious application of varied matured compost types as organic fertilizers into soil systems.