3.1. Crop yield
Compared to the 30-cm topsoil depth, maize yield under the 10-cm topsoil depth decreased by 22%, 11% and 9% in 2016, 2017 and 2018, respectively (P < 0.05, Fig. 1a). Yield under the 20-cm topsoil depth significantly decreased only in 2016 (P < 0.05, Fig. 1a). Soybean yield did not decrease under the 10-cm topsoil depth, compared to the 30-cm topsoil depth. However, the 20-cm topsoil depth significantly increased yields in 2016 and 2018 (P< 0.05, Figs 1b & S1).