The effects of worms, clay and biochar on CO<sub>2</sub> emissions during production and soil application of co-composts

Abstract

Abstract. In this study we evaluated CO 2 emissions during composting of green wastes with clay and/or biochar in the presence and absence of worms (species of the genus Eisenia), as well as the effect of those amendments on carbon mineralization after application to soil. We added two different doses of clay, biochar or their mixture to pre-composted green wastes and monitored carbon mineralization over 21 days in the absence or presence of worms. The resulting co-composts and vermicomposts were then added to a loamy Cambisol and the CO 2 emissions were monitored over 30 days in a laboratory incubation. Our results indicated that the addition of clay or clay/biochar mixture reduced carbon mineralization during co-composting without worms by up to 44 %. In the presence of worms, CO 2 emissions during composting increased for all treatments except for the low clay dose. The effect of the amendments on carbon mineralization after addition to soil was small in the short term. Overall, composts increased OM mineralization, whereas vermicomposts had no effect. The presence of biochar reduced OM mineralization in soil with respect to compost and vermicompost without additives, whereas clay reduced mineralization only in the composts. Our study indicates a significant role of the conditions of composting on mineralization in soil. Therefore, the production of a low CO 2 emission amendment requires optimization of feedstocks, co-composting agents and worm species.

Composting with additives to improve organic amendments. A review

“…Biochar addition during composting has contradictory effects on CO 2 emissions compared to regular compost, either increasing (Czekała et al 2016;Wu et al 2017) or decreasing them (Chowdhury et al 2014). Such contradictory effects were also observed for vermicomposting (Barthod et al 2016). Organic additives in the form of bulking materials, such as plastic or pumice, increase CO 2 emissions through aeration improvement and microbial activity enhancement (Wu et al 2015;Czekała et al 2016).…”

“…When choosing organic additives, attention must be paid to the C/N ratio of the initial mixtures to ensure organic matter degradation and prevent N leaching during composting (Doublet et al 2011). Furthermore, biochar, a highly aromatic pyrolysis product (Lehmann and Joseph 2015), has recently received great interest as highly stabilised organic additive for composting (Dias et al 2010;Waqas et al 2017) and vermicomposting (Malińska Barthod et al 2016). As the production of biochar was shown to yield highly aromatic materials with high stability when added to soil, biochar may enhance the carbon sequestration potential of composts and vermicomposts (Lehmann et al 2006;Lehmann 2007), thus mitigating climate change.…”

“…Pure zeolite is easily synthesised by the slow crystallisation of a silica-alumina matrix. Finally, pure minerals such as clay, extracted from quarries or soils, are increasingly used with the aim of reducing greenhouse gas emissions during composting (Bolan et al 2012;Barthod et al 2016). These minerals are sometimes added during vermicomposting (Li et al 2009;Hayawin et al 2014;Barthod et al 2016).…”

“…In conclusion, reducing CO 2 emissions from composting without altering the biodegradation process appears difficult. Chemical and mineral additives have the potential to limit CO 2 emissions, for example by trapping emitted CO 2 with an adsorbent, such as red mud, or by protecting carbon from decomposition through associations with clays or amorphous hydroxyl-Al (Bolan et al 2012;Haynes and Zhou 2015;Barthod et al 2016).…”

“…Additives are used to enhance the composting process by reducing leaching (Steiner et al 2010) and gas emissions (McCrory and Hobbs 2001;Awasthi et al 2016a, b), improving compost aeration or accelerating organic matter degradation (Sánchez-García et al 2015) and improving nutrient content and availability in the final product (Gabhane et al 2012;Morales et al 2016). Only few studies assessed the effect of additives on vermicomposting (Wang et al 2014; Barthod et al 2016;Malińska et al 2017) (Fig. 1).…”