Greenhouse Gas Production in Mixtures of Soil with Composted and Noncomposted Biochars Is Governed by Char-Associated Organic Compounds

Abstract

Biochar application to soil has the potential to increase soil productivity while reducing anthropogenic greenhouse gas (GHG) emissions to the atmosphere. However, techniques for conditioning this material for maximizing its effects as a soil amendment require elucidation. We examined changes of organic matter associated with two biochars after 175 d of composting and the resulting effects on GHG emissions during a 150-d incubation period. Composting decreased the amount of organic compounds that could be thermally released from the biochars and affected their molecular nature. These thermally desorbable organic compounds from initial biochars likely stimulated the oxidation of CH and inhibited the production of NO in soil-biochar mixtures. However, these reductions of GHG emissions disappeared together with thermally desorbable organic compounds after the composting of chars. Instead, addition of composted gasification coke and charcoal stimulated the formation of CH and increased NO emissions by 45 to 56%. Nitrous oxide emissions equaled 20% of the total amount of N added with composted biochars, suggesting that organic compounds and N sorbed by the chars during composting fueled GHG production. The transient nature of the suppression of CH and NO production challenges the long-term GHG mitigation potential of biochar in soil.

Effects of temperature and processing conditions on biochar chemical properties and their influence on soil C and N transformations

“…3a). These results suggest that the presence of labile forms of organic C contained in biochars produced at pyrolysis temperatures <400 C, such as VOC and sorbed organic compounds, promoted N 2 O emissions (Deenik et al, 2010;Ameloot et al, 2013;Borchard et al, 2014).…”

Biochar‐compost substrates in short‐rotation coppice: Effects on soil and trees in a three‐year field experiment

“…While the latter effect may involve N fixation, N deposition, and particularly N return from deep roots via shoots and leaves back to the surface soil, we suggest considering the differences between the control and TPS‐treated soils that the addition of biochar–compost substrates reduced N losses. Cayuela et al (2014) pointed out that biochar application to soil can decrease N 2 O emissions by 54%, although this has not been confirmed consistently ( e.g ., Case et al, 2014; Borchard et al, 2014b). Furthermore, the significantly higher pH of the biochar treatments possibly reduced denitrification as well as N 2 O emission sustaining higher TN stocks of the treatments ( Zhang et al, 2010).…”

“…Conversely, the absence of such positive effects as well as even negative effects on crop yield have also been reported ( e.g ., Van Zwieten et al, 2010; Crane‐Droesch et al, 2013; Borchard et al, 2014a); in addition, other studies have found that woody crops did not respond to biochar applications under temperate climate conditions ( Schmidt et al, 2014; Teat et al, 2015). Some of these negative effects have been attributed to phytotoxicity of the biochars or to nutrient imbalances ( e.g ., Ding et al, 2010; Taghizadeh‐Toosi et al, 2011; Borchard et al, 2014b). These limitations may be overcome by combining biochar application with compost ( Steiner et al, 2010; Fischer and Glaser , 2012).…”

Effect of Pine Waste and Pine Biochar on Nitrogen Mobility in Biosolids

“…Volatile organic compounds (VOCs) may be present in biochars and sawdust (Spokas et al, 2011) and can potentially reduce nitrification (Clough et al, 2010) and mineralization. Borchard et al (2014) demonstrated that VOCs from biochar influence N cycle and can reduce greenhouse gas emissions from soil. The fact that the NO 3 − –N leached as a percentage of N applied was higher ( p < 0.05) under the biochar treatments than in the biosolids alone (Fig.…”