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

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 (T 1 ), 120 (T 2 ), and 180 (T 3 ) earthworms per kilogram of substrate. A traditional composting system without earthworms was set as a control (T 0 ). The results indicated that earthworms increased CO 2 while decreased CH 4 and N 2 O emissions compared to the control. Higher emission of CO 2 suggested that the earthworms promoted the degradation of the substrates. Lower emission of CH 4 and N 2 O showed the advantage of the combined system because CH 4 and N 2 O possess extremely higher global warming potential than that of CO 2 . T 2 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 T 1 , T 2 , and T 3 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.