Abstract
Recently special attention has been paid to the humification of organic wastes during composting to evaluate maturity and quality of products. The effects of composting period and degree of maturity on production and optical characteristics of humic substance and structural features of humic acid in practically processed cattle manures were investigated. Beef cattle manure, which were mixed with bark litter and well composted (bark compost) by monthly turning for 5 and 12 months, were selected to evaluate effects of composting periods on the humification. Relative color density (RF value) of humic acid in bark composts increased with increase in the duration of composting. Optical characteristics and structural features of humic acids extracted by water and NaOH solution from four selected dairy and beef cattle manures, which showed completely different degree of maturity, were compared. Humic acids extracted by NaOH solution from dairy cattle manures, which were extremely high in moisture and not aerobically composted, were classified into the immature Rp-type and characterized by lignin-like structures from UV-VIS and FT-IR spectra. Aerobically fermented and well-matured beef cattle manure contained the humified B-type humic acid, which was characterized by carboxylic group and amide structures. These functional groups were more remarkable in the water-extracted humic acids than NaOH-extracted ones. It was concluded that practically well processed and matured cattle manure, which had been selected in the present study, contained highly humified organic matter compared to those reported in the previous studies, probably due to high temperature and its own heavy weight on a large scale.
