MM with different N application rates (A), IM with different N application rates (B); the X-axis indicates depth (20 cm per layer) and the Y-axis indicates sampling interval (10 cm per interval); N application rates are 0, 180 kg N ha-1 (shared by soybean and maize), and 240 kg N ha-1 (180 kg N ha-1 for maize and 60 kg N ha-1 for soybean), respectively, the same as below.