Fig. 1. Effect of topsoil depth on grain yields of maize and
soybean in 2016, 2017 and 2018. The main effects of topsoil depth, crop
species and cropping year, and their interactions are all highly
significant (P < 0.001). Values with means ± standard
error (n=3). Within a growing season of each panel, values with a same
letter are not significantly different (P > 0.05).