Fig. 4

WICST SOC stock change from 1989 to 2009 as estimated by FD and ESM. Average change from 1989 to 2009 in SOC stocks (Mg C ha⁻¹) by soil depth in each WICST treatment (n = 12 for Maize, n = 18 for MS, n = 33 for MSW, n = 39 for MAAA, and n = 27 for MOA) as estimated by both FD and ESM. Maize is a high-external input, continuous corn system, MS is a moderate, external input, no-till corn-soybean system, MSW is an organic corn–soybean–winter wheat with interseeded red clover system, MAAA is a high-input corn–alfalfa system, and MOA is an organic oats/alfalfa-corn system. 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