Fig. 3

Century wheat SOC stock change from 1993 to 2012 as estimated by FD and ESM. Average change from 1993 to 2012 in SOC stocks (Mg C ha⁻¹) by soil depth in each wheat Century treatment (n = 6 per treatment) as estimated by both FD and ESM. IWC is irrigated wheat–fallow with winter supplemental irrigation and no fertilizer inputs, IWF is irrigated wheat–fallow with supplemental irrigation and N fertilizer, RWC is rainfed wheat–fallow control with no additional inputs, RWF is rainfed wheat–fallow and N fertilizer, and RWL is rainfed wheat–fallow with WCC planted after wheat harvest and terminated before summer fallow. We report the results as “ESM depth” intervals [8]. These intervals are the depths represented by the reference soil masses used for the ESM calculation. The reference mass is defined as the mass from the initial fixed depth sample averaged across treatment replicates. Reference masses for each treatment and depth interval can be found in Additional file 1: Table S1a. Error bars represent 95% confidence intervals