Fig. 4. Effect of topsoil depth on N, P and K uptake per unit root length of maize at the jointing (V7) and milk (R3) stages, and of soybean at the initial flowering (R1) and seed-filling (R6) stages in 2017. Values with means ± standard error (n=3). Within a growth stage of each panel, values with a same letter are not significantly different at (P > 0.05).