Fig. 1 Soil organic C (SOC) as affected by (a) the interaction of tillage x depth, (b) the main effect of tillage, and the interaction of tillage x depth x sand content in the (c) surface (0–5 cm) and (d) subsurface (5–15 cm) depths. The lines in (c) and (d) represent the linear response of tillage x depth to sand content used as a covariate