Texture and organic carbon relations described by a profile pedotransfer function for Brazilian Cerrado soils

Little is known about the interdependence between soil organic carbon (SOC) and texture within the soil profile. In order to describe mathematically this relation, three highly weathered soils (sandy, loamy and clayey) in the Brazilian Cerrado under similar climate, vegetation and topography were sampled in triplicate to 1-m depth and analyzed for texture and total SOC concentration. The SOC concentration was directly and linearly correlated with the combined clay + silt (but not to clay) content for all depths. The intercept and slope of these linear relations decreased with depth following exponential and logarithmic functions (P < 0.001, R2 = 0.97 and 0.95, respectively). These mathematical functions permitted the adjustment of the intercept and slope parameters of a SOC = a + b(clay + silt) function for any depth in the 0-1 m interval. This profile pedotransfer function precisely estimated SOC concentration (P < 0.0001, R2 = 0.92) up to 1.0 m of the studied soils. Using data from different Cerrado soils, estimated vs. measured SOC relations with similarly high R2 values were obtained, despite slopes and intercepts were different than 1 and 0. This indicates that for the Cerrado region the textural control of SOC varies predictably with depth, and the proposed model can be calibrated to estimate SOC in subsurface layers of highly weathered soils.