Humification and Degradability Evaluation During Composting of Horse Manure and Biowaste

Abstract

Performing compost quality assessment such as compost stability is quite necessary for rating the quality of horse manure and biowaste composts and meeting specific regulatory requirements on the composition and compost process. The aim of this study was to identify an appropriate feedstock composition for use in the production of high quality compost. The objectives were to (1) identify an appropriate feedstock composition (2) determine organic matter decomposition and humic acids (HA) development in various composts; (3) compare changes in temperature, C/N ratio and respiration activity, occurring during decomposition of organic matter; (4) evaluate phytotoxicity effects of the final compost on cress seed germination and growth. The above changes in physical, chemical and biological parameters were monitored during the laboratory composting process over a period of 20 weeks. Five organic waste blends of horse manure (HM) and biowaste (BW) were used. The results indicated that at the beginning of the experiment, the highest C/N ratio of 59 was recorded in the pure horse manure. This is attributed to the presence of higher amounts of bedding materials (wood chips and wheat straw). The degradation rate of pure HM was slower than that of BW and the degradation had not been completed by the end of the 20 weeks composting period. An ANCOVA with time as the covariate showed that pure BW was more significantly humified than pure HM (p<0.05). Consistently higher contents of HA and lower E4/E6 ratio were obtained in pure BW than in pure HM throughout the processes. Statistically significant difference (p<0.01) among treatments were found for the shoot fresh weight percentage (SFW%). Correlations between the latter and E4/E6 ratios were significant at (p<0.001). Chemical and biological changes indicated an increase in compost quality in correspondence with BW composition increment. Largely the 50/50 blend was not significantly different from other feedstocks (p<0.01) except from pure HM. It was therefore concluded that composting using a combination of HM and BW (50/50) could be used as an alternative method to pure HM composting.