Depth distribution of the soil organic carbon (SOC) concentration under different tillage practices.

<p>No till (NT), rotary tillage (RT), and plow tillage (PT): (A) after the maize harvest and (B) after the wheat harvest. The data are presented as the means ± SD (n = 3). The various capital letters indicate significant differences among the soil depths, and the lowercase letters indicate significant differences among the treatments (<i>P</i><0.05).