Soil organic carbon sequestration potential of Pampean soils: comparing methods and estimation for surface and deep layers

Abstract

Estimates of soil carbon sequestration potential can help identify areas where appropriate use and management practices can be applied to convert them into carbon sinks. We estimated the carbon capacity of Pampean soils using previously developed models and compared the results with a local model developed by simultaneous quantile regression. We also modelled the effects of the factors controlling the carbon saturation deficit using artificial neural networks and mapped the topsoil and subsoil saturation deficit of the region. Data from a soil survey, in which 296 sites were sampled to 1 m depth, were used. Paired sites in grassland, cropland and lowland areas were selected. The total organic carbon was measured, and the proportion stabilised in the clay + silt (<20 µm) fraction was estimated. The saturation deficit could be predicted (R2 = 0.78) by neural networks and was greater in cropland, followed by lowland and then grassland. It was higher in fine textured soils, in soil surface layers and in humid and colder environments. The saturation deficit of the region is 8.8 Gt carbon (average 196 Mg C ha–1), approximately double the current organic carbon content of the region, indicating that there is considerable room for carbon sequestration in the Pampas. Efforts to increase soil carbon levels must focus on the finely textured soils in the humid part of the region.