3.4. Specific nutrient uptake rate
In maize, the N, P and K uptake per unit root length under 10 cm of topsoil depth significantly decreased by 44%, 46% and 57% at V7, respectively, compared to 30 cm of topsoil depths (P < 0.05, Fig. 4). There was no difference in the P and K uptake per unit root length between 30 cm and 20 cm of topsoil depths at V7. An increase in the N and K uptake per unit root length was found under 20 cm of topsoil depths compared to 30 cm of soil depth at R3.
In soybean, the N, P and K uptake per unit root length under 10 cm of topsoil depth was 46%, 42% and 50% lower than under 30 cm of topsoil depths at R1, respectively. The N, P and K uptake was 71%, 69% and 74% lower under 20 cm and 53%, 45% and 57% lower under 10 cm of topsoil depths than under 30 cm of topsoil depth at R6, respectively (P < 0.05, Fig. 4d, e, f).
The total root length in top 10-cm layer increased with decreasing topsoil depth for maize at V7 and soybean at R1. The total root length was maximum under 20-cm topsoil depth for maize at R3 and soybean at R6 (Fig. S2).