Impact of bentonite on greenhouse gas emissions during pig manure composting and its subsequent application

Additives were widely investigated to retain the nutrients and mitigate the greenhouse gas emissions (GHGs) during manure composting. However, the sustained effects of additives on the GHGs emissions following incorporation of composts to soil were scarcely explored. This study evaluated the effects of bentonite added at the beginning of pig manure composting on the GHGs emissions during two successive processes, i.e., composting and soil incubation amended with composting products. Addition of bentonite did not hinder the composting process and alter the total CO₂ emission. On the other hand, reduction by about 17% and 29% for CH₄ and N₂O emission, respectively, was achieved in the presence of bentonite during composting. Incorporation of the final composting products to soil enhanced significantly the soil C and N of various forms, and gas emissions of CO₂ and N₂O. However, no significant differences were observed between bentonite-manure co-compost and manure-only compost application except for the N₂O emission. Compared to the manure-only compost, compost amended with bentonite reduced N₂O loss by around 6.8%, but not statistically significant. This study confirmed that addition of bentonite at the composting stage can mitigate the GHGs emission considering both composting and compost application stages, with all reductions occurring at the composting stage.