Fig. 4: Conceptual representation of different regression methods to estimate the effective mineral-associated organic carbon (MAOC) capacity.
From: Revisiting the soil carbon saturation concept to inform a risk index in European agricultural soils
Boundary line (BL) assumes that MAOC content (g C kg−1 in fine fraction (ff)) has a constant maximum across the fine fraction range15. Piece-wise boundary line (PBL) assumes a constant for the effective MAOC capacity (like Feng et al.) but isolates the disturbance of MAOC contamination and organo-organo C bonds. The non-linear boundary line (NBL) assumes that MAOC content can change across the fine fraction range; effective MAOC capacity includes SOC organic layers that interact via organo-organo C bonds rather than directly to the clay surface. All regressions were done for the 90th quantile with a forced intercept to 0 as per Feng et al. Data and fitting statistics for the LUCAS survey is presented in Supplementary Figs. 5–7.
