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Humic Substances Formed during the Composting of Organic Matter
Author(s) -
Inbar Y.,
Chen Y.,
Hadar Y.
Publication year - 1990
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1990.03615995005400050019x
Subject(s) - chemistry , compost , humus , magic angle spinning , fourier transform infrared spectroscopy , humic acid , fractionation , manure , decomposition , organic matter , chemical composition , nuclear chemistry , nuclear magnetic resonance spectroscopy , chromatography , stereochemistry , organic chemistry , soil water , agronomy , fertilizer , physics , environmental science , quantum mechanics , biology , soil science
Humic substances (HS) were extracted from separated cattle‐manure compost (CSM) at various stages of decomposition. Carbon‐13 nuclear magnetic resonance ( 13 C‐NMR) and Fourier‐transform infrared (FTIR) spectroscopy measurements were performed on the purified humic acids (HA) as well as crude fiber and chemical analyses. Levels of HS extracted from the CSM samples doubled during the composting (from 377 to 710 g kg −1 organic matter [OM]). The HS were divided into: (i) HA, which increased from 184 to 457 g kg −1 OM; and (ii) a fulvic fraction (FF). The FF was separated on XAD‐8 resin to: (i) fulvic acid (FA), which maintained an unchanged level during composting (80–100 g kg −1 ); and (ii) a nonhumic fraction (NHF), which increased from 107 to 170 g kg −1 OM during the process. The ratios between the concentrations of these fractions were tested as humification indexes. These indexes changed significantly during the process and were found to correlate exponentially with the composting time, C/N ratio, or both. Quantities of low‐molecular‐weight components (FF and NHF) rapidly increased during the first 40 d of composting and were nearly constant thereafter. The HA and HS contents reached nearly constant values after ∼90 d. Only slight compositional and structural changes in CSM HA were detected with cross‐polarization magic‐angle spinning (CPMAS) 13 C‐NMR, FTIR spectra, and chemical analyses. The elemental composition and functional groups of CSM HA resembled those reported for HA of plant residues, peats, and incompletely humified materials. The CPMAS 13 C‐NMR spectra of the CSM HA resembled that of lignin. The aromaticity of the HA was about 40% and the lignin content was approximately 60%. The NMR data correlated well with results obtained by FTIR spectroscopy, both indicating that the CSM HA are composed of partially degraded constituents of plant tissue, which still retain to some extent their chemical structures. The major plant components identified in the HA were lignin, carbohydrates, and long‐chain aliphatic structural groups.