Measurement and simulation of the water flow and root uptake in soil under subsurface drip irrigation of apple tree

Abstract The study of water flow and root uptake under the soil is especially important in subsurface drip irrigation. The main objective of this study was to measure water flow and root uptake under the soil in subsurface drip irrigation and simulation based on different scenarios in HYDRUS-2D. The field experiment was carried out in a land around a 30-year-old apple tree with a 2 m × 2 m plot in 2018. The emitters were installed at a depth of 30 cm and a distance of 1 m from the tree trunk. The soil water content was measured using a TDR device. It was measured daily for 4 months at the depths of 25, 50, 75 and 100 cm. In order to calibrate the root equation parameters, the samples of root with soil were collected from different parts of the root development zone. The results showed that the highest and lowest root water uptake occurred in the coordinates (radial, deep), (60 cm, 50 cm) and (150 cm, 75 cm) from the tree trunk, respectively. Approximately 81% of the root uptake was at a depth of 0–50 cm and only 19% was at a depth below 50 cm. The calculated RMSE, (0.0141–0.0193 cm3cm−3) showed that HYDRUS-2D had a good estimate from of the soil water content in subsurface drip irrigation. Comparison of different simulated scenarios by HYDRUS-2D with the results of the field measurements showed that by decreasing the emitter discharge to 2 lit h−1 and increasing the irrigation duration (in the constant amount of water used), the root water uptake was raised by 5.08%, and while deep penetration was decreased by 2.18%, as compared to the real condition.