Abstract
AbstractAs studies on biochar stability in field conditions are very scarce, the carbon sequestration potential of biochar application to agricultural soils remains uncertain. This study assessed the stability of biochar in field conditions, the effect of plant roots on biochar stability and the effect of biochar on original soil organic matter (SOM) decomposition in two (Italy and United Kingdom) short rotation coppice systems (SRCs), using continuous soil respiration monitoring and periodic isotopic (δ13CO2) measurements. When root growth was excluded, only 7% and 3% of the biochar carbon added was decomposed after 245 and 164 days in Italy and United Kingdom sites respectively. In the presence of roots, this percentage was increased to 9% and 8%, suggesting a small positive priming effect of roots on biochar decomposition. A decreased decomposition rate of original SOM was observed at both sites after biochar incorporation, suggesting a protective effect of biochar on SOM. This study supports the carbon sequestration potential of biochar and highlights the role of root activity on biochar decomposition, questioning the applicability of laboratory incubation studies to assess biochar stability.
Highlights
Biochar is a carbon-rich material produced from pyrolysis or gasification of biomass under low oxygen conditions (Lehmann, 2007)
In the UK site, Rtot was significantly higher with biochar, while no effect of biochar was detected for Rh (Table 2)
Considering that we found a positive relationship between soil respiration and soil water content (SWC) in both sites, a higher SWC in trenched and biochar-treated plots probably led to an overestimation of RhB, and to an underestimation of the Peff-biochar [Eqn (5)]
Summary
Biochar is a carbon-rich material produced from pyrolysis or gasification of biomass under low oxygen conditions (Lehmann, 2007). The potential of biochar to improve soil C-sink is still under debate, since its stability seems to depend on several factors, such as the starting feedstock, pyrolysis conditions, soil environment and vegetation cover of the site (Hilscher & Knicker, 2011). Several short-term incubation experiments (Hamer et al, 2004; Cheng et al, 2008a; Kuzyakov et al, 2009; Zimmerman, 2010) suggest centennial or millennial mean residence times for biochar stability. Most of the experiments on biochar stability are based on short-term lab incubations while field studies remain scarce (Jones et al, 2012; Gurwick et al, 2013). Little is known about the interactions between biochar and roots and the related effects on biochar stability (Ventura et al, 2013)
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