The non-negligibility of greenhouse gas emission from a combined pre-composting and vermicomposting system with maize stover and cow dung.

Abstract

The acceptance of combined pre-composting and vermicomposting systems is increasing because of the advantage in rapidly stabilizing organic wastes and reducing emission of greenhouse gasses (GHG). However, GHG emission during the pre-composting phase is often neglected when evaluating the system. This study aimed to quantify GHG emission from a combined pre-composting and vermicomposting system and to investigate the effects of earthworms on GHG emission. A combined system using Eisenia fetida was employed to stabilize maize stover and cow dung (mixing ratio 60:40). The inoculating densities were 60 (T1), 120 (T2), and 180 (T3) earthworms per kilogram of substrate. A traditional composting system without earthworms was set as a control (T0). The results indicated that earthworms increased CO2 while decreased CH4 and N2O emissions compared to the control. Higher emission of CO2 suggested that the earthworms promoted the degradation of the substrates. Lower emission of CH4 and N2O showed the advantage of the combined system because CH4 and N2O possess extremely higher global warming potential than that of CO2. T2 is recommended for stabilizing maize stover and cow dung when making a tradeoff between stabilization rate and reduction of GHG. The percentages of GHG emission during pre-composting relative to total GHG emission in T1, T2, and T3 were 34%, 35%, and 30%, respectively. GHG emission is non-negligible when using a combined system, especially the emission of GHG during the pre-composting phase cannot be ignored.