Solid-state carbon-13 nuclear magnetic resonance and infrared spectroscopy of composted organic matter

Use of stabilized composts as horticultural container media has been a fruitful and desirable alternative in utilization of agricultural wastes. We prepared compost from cattle manure and investigated the products at various stages of the composting process. The objectives of this work were to measure, quantify and correlate changes in the organic constituents of separated cattle manure (CSM--the solid fraction obtained by centrifugal separators from a slurry of cattle manure) during composting by using both chemical and spectroscopical analytical methods. This research should provide the information necessary for the establishment of maturity indexes for CSM. Carbon-13 NMR spectra acquired with Cross-Polarization Magic Angle Spinning (CPMAS) and infrared spectra measured with a Fourier-Transform InfraRed spectrophotometer (FTIR) were applied to bulk CSM samples without extraction. Both methods confirmed the presence of appreciable amounts of carbohydrates throughout the composting process. During the process the level of carbohydrates decreased while levels of alkyl C, aromatic C, and carboxyl groups increased. The higher rate of decomposition of the carbohydrates resulted in the accumulation of modified lignin. Changes in FTIR absorbance ratios of several distinct peaks were linearly and significantly correlated with various parameters of compost maturity. Crude fiber analyses showed lower concentrations of soluble organic matter, hemicellulose and cellulose while that of lignin increased. Cation exchange capacity increased from 63 to 181 cmol/kg OM, and humic substances content increased markedly from 38 to 71% of the organic matter, while the C/N ratio decreased from 27.1:1 to 8.7:1 during the 147-d composting process. The proposed spectrometric procedures using CPMAS 13C-NMR and FTIR measurements directly on decomposing organic matter without extraction, provide information exhibiting significant correlations with more conventional chemical parameters of compost maturity.