3.5. Available nutrients in the rhizosphere
The concentrations of available N and P in the rhizosphere of maize were 42% and 36% lower, respectively, under the 10-cm than the 30-cm topsoil depth (P < 0.05, Fig. 5a, b). Topsoil depth did not affect available K (P > 0.05, Fig. 5c). In comparison, the concentrations of available N, Olsen P and available K in the rhizosphere of soybean were 12%, 25% and 19% lower under the 10-cm than the 30-cm topsoil depth, respectively (P < 0.05, Fig. 5a, c). However, there was no difference in concentrations of available N, P and K between the 30-cm and 20-cm topsoil depths (P > 0.05, Fig. 5c).