The effects of worms, clay and biochar on CO2 emissions during production and soil application of co-composts

In this study we evaluated CO2emissions during composting of green wastes with clay and/or biocharin the presence and absence of worms (species of the genusEisenia), as well as the effect of those amendmentson carbon mineralization after application to soil. We added two different doses of clay, biochar or their mixtureto pre-composted green wastes and monitored carbon mineralization over 21 days in the absence or presenceof worms. The resulting co-composts and vermicomposts were then added to a loamy Cambisol and the CO2emissions were monitored over 30 days in a laboratory incubation. Our results indicated that the addition ofclay or clay/biochar mixture reduced carbon mineralization during co-composting without worms by up to 44 %.In the presence of worms, CO2emissions during composting increased for all treatments except for the lowclay dose. The effect of the amendments on carbon mineralization after addition to soil was small in the shortterm. Overall, composts increased OM mineralization, whereas vermicomposts had no effect. The presence ofbiochar reduced OM mineralization in soil with respect to compost and vermicompost without additives, whereasclay reduced mineralization only in the composts. Our study indicates a significant role of the conditions ofcomposting on mineralization in soil. Therefore, the production of a low CO2emission amendment requiresoptimization of feedstocks, co-composting agents and worm species