Humic substances formation during poultry litter composting and its influence on the structural characteristics of the compost

This study aimed to elucidate the formation process of humic substances (HS) during poultry litter (PL) composting and its influence on the structural characteristic of the formed compost. Fresh PL was composted, and samples were collected at seven time points (0, 7, 21, 30, 60, 90, and 120 days). At each time point, the compost and its humic fractions were characterized by elemental composition, FTIR spectroscopy, and 13 C nuclear magnetic resonance spectroscopy ( 13 C-NMR CP/MAS) and analyzed by principal component analysis (PCA) and multivariate curve resolution (MCR). The compounds solubilized during composting were characterized by proton nuclear magnetic resonance ( 1 H-NMR) and heteronuclear single quantum coherence spectroscopy ( 1 H- 13 C HSQC). The results showed that PL composting started with the decomposition of nitrogenous compounds (C Alkyl -O,N) followed by the decomposition of carbohydrates (C Alkyl -O e C Alkyl - di -O). However, part of these peptide and carbohydrate fragments act as HS precursors and are selectively preserved in the humic acid (HA) structure. Thus, HA structures evolve from lower molecular weight fulvic acid. The preservation of labile and nitrogenous structures in the HA contributes to the preservation of these structures in the final compost. Carbohydrates and peptides are also solubilized and leached, producing liquid humus rich in monosaccharides and amino acids.