Critical questions about the rate, duration and ultimate limits (i.e. saturation) to soil C stabilization remain. Especially the concept of soil C saturation needs to be further investigated. In previous work, we found that: 1) the dependency of the fundamental kinetics of soil C turnover on SOC levels, a basic tenet of the saturation hypothesis, is a general phenomenon and 2) differences in the relative efficiency by which newly added C is stabilized in discrete, physically-fractionated SOC components is consistent with the saturation hypothesis and. In the current project we further elucidate how C saturation level and ‘saturation-deficit’ govern the capacity of the soil C sink and the time period over which it can be exploited for C sequestration. The major hypothesis underlying our newly proposed work is that C sequestration amounts are determined by the steady-state C level for a specific management-soil-climate condition, but that the rate, duration and C input level required to attain this C sequestration capacity is controlled by the soil C saturation level and saturation-deficit. Further we postulate that the parameters controlling the rate and capacity of C stabilization can be quantified through measurement of specific SOC fractions and can be used in a new theory/model of C stabilization and turnover as a function of climate, C inputs, soil disturbance, soil texture and mineralogy.

For more information contact Johan Six (jwsix@ucdavis.edu) or Haegeun Chung (hgchung@ucdavis.edu) or consult the publication: Six et al. 2002. Stabilization mechanisms of soil organic matter: Implications for C-saturation of soils. Plant and Soil 241:155-176. (PDF file)