mg ha

carbon soc

carbon storage

organic carbon soc

soc stocks

soc dynamics

soil sampling

Soil & Tillage Research

Increasing soil organic carbon (SOC) stocks via land management has been proposed as a temporary climate change mitigation measure. An upper limit of soil stable SOC storage, which refers to the concepts of SOC saturation has been proposed. Using systematic grid sampling of topsoil in mainland France and an equation that predicts this SOC saturation, we derived estimates of the SOC sequestration potential density (SOCspd) for various land uses. First, using French database and data from the literature we estimated the proportions of the SOC stored in the fine fraction (SOCfine) in total SOC for grassland (69%), cropland (85%) and forest (66%). Then, SOCspd was calculated as the difference between the theoretical SOC saturation value and SOCfine. The SOCspd stocks for French topsoil were estimated at about 1.1 Pg, in which cropland, forest and grassland accounted for 66%, 17% and 17%, respectively. Varying the proportions of SOCfine in the calculations by assuming a possible range of 0.8-0.9 for cropland and 0.6-0.9 for grassland and forest soils led to variations of total SOCspd stocks of about 0.1 Pg for each land use. Most importantly, we demonstrate that the distribution of SOCspd in forest soils is exactly centred at zero, which suggests that on average, forest topsoils are saturated in SOCfine, and thus Hassink’s equation provides a valid estimate for the SOC sequestration potential for French topsoil.

Soil carbon stocks under different land uses and the applicability of the soil carbon saturation concept