Characteristics of dissolved organic matter release during green manure decomposition

Soil dissolved organic matter (DOM) which can characterize soil quality, plays an important role in the soil carbon and nitrogen cycle, reflecting soil quality to a certain extent. This study combined the fluorescence excitation-emission spectrum and parallel factor analysis (EEM-PARAFAC) to analyze DOM content, composition, and spectral characteristics during decomposition of grass species on the Loess Plateau, which could providing data and theoretical support for soil quality and management evaluation of orchards. The decomposition rate followed the order: white clover (Trifolium repens) (WC) > crown vetch (Securigera varia Lassenn) (CV) > orchard grass (Dactylis glomerata) (OG). EEM-PARAFAC identified one humic acid-like component (C1) and two protein-like components (C2, C3). The fluorescence intensity of the protein-like components was much higher than that of the humic acid-like component, and the C2 was dominant component. The total fluorescence intensity of the WC treatment was higher than that of the OG and CV treatments. The main source of DOM in CV was microbial, while those of WC and OG were terrestrial plant humus and microbial. The humification index (HIX) value followed the order: CV > OG > WC. The SUVA₂₅₄ values followed the order: OG > CV > WC and increased with decomposition. According to the DOM content, composition, spectral characteristics, as well as principal component analysis results, white clover was more beneficial regarding decomposition and release of dissolved organic nutrients in Weibei drylands.