Fig. 3. Corn-derived C4-C expressed as (A) concentration (g C kg^–1 soil) or (B) mass (Mg C ha^–1 soil) for no-till (NT) or conventional (moldboard plow) tillage (CT) with residues returned (+) or residues removed (–). Error bars represent standard error. Means with the same letter are not significantly different at a probability of 0.05. Statistics performed separately for the 0- to 15-cm depth.