Physical and chemical maturity indexes and Fourier transform infrared (FTIR)spectroscopy of animal manures during composting.

Abstract

The composting experiments on three manures (cattle, pig and chicken manures) were carried out to study the maturity indexes by monitoring their physical and chemical properties, seed germination index (GI), and characterizing chemical structures using Fourier transform infrared (FTIR) spectroscopy. Results showed that temperature changed during composting, and the numbers of peak temperatures for cattle, chicken, and pig manures were 1, 2 and 2, respectively. The duration with temperature higher than 50 ℃ was longer than 10 days for all the three manures. This indicated that temperature was the most intuitive maturity index. The pH of pig and chicken manures increased from 6.63 to 7.74 and from 7.73 to 8.66, respectively, while that of cattle manure first increased from 7.86 to 8.36 and then decreased to 7.52. The organic carbon content decreased by23.3%, 28.2%, and 31.7%, respectively, for cattle, pig and chicken manures. In addition, the NH4+-N concentrations decreased by 87.8%, 73.6%, and 79.7%, and the NO3--N increased by 56.81, 6.49, and 4.85 times for cattle, pig, and chicken manures, respectively. The ratio of NH4+-N/NO3--N of piles decreased below 2. Our study indicated that temperature, pH, organic carbon content, and ratio of NH4+-N/NO3--N were closely related to maturity index and correlated with seed germination rate (P≤0.05). The FIIR spectra revealed that in the cattle and pig manures aliphatic compounds and polysaccharides decreased but aromatics increased during the process of composting, suggesting enhanced humification. However, the trend was reversed for chicken manure. Therefore, it was necessary to take into account the stability of composts while maturity indexes were sought.