Sohi, Saran (Agriculture & the Environment Division, West Common, Harpenden, Herts, AL5 2JQ, United Kingdom; Phone: +44 (0)1582 763133 ext.2665; Fax: +44 (0)1582 760981; Email: saran.sohi@bbsrc.ac.uk)

Accounting for Black C in the Modeling of Soil Organic Matter Turnover

S Sohi *, J Gaunt, H Yates, J Lehmann

According to recent estimates, black C is a much larger component of soil organic carbon (SOC) in typical agricultural soils than previously assumed. Since black C may also be the most stable form of organic C in the soil, the amount of black C in the soil must impact both on the bulk rate of soil C mineralization (turnover), and the extent to which a particular management intervention can alter SOC.

Simulation models that explicitly account for the impact and interaction of soil and environmental variables can assist in predicting the accumulation of C and its rate of turnover. Relevant, verifiable (i.e. measurable) pools of soil organic matter (SOM) provide the most robust basis for elucidating the underlying mechanisms. We have developed a model based around three measurable pools of SOM, which can be measured using a density-based fractionation procedure. The model has been optimized against measurements of C and N and isotope-tracers in several soils amended with isotope-labeled organic matter.

Until now our simulations have not accounted explicitly for the effect of black C on the dynamics of each pool. It seems unlikely that black C is characterized by a particular physical location within the soil matrix, and in order to account for the influence of black C using this model we have been developing methods to establish how black C influences C turnover and to establish the distribution of charcoal between each of the measured fractions. We will use the data gathered to assess the net impact of black C on soil C turnover.