Calibration of HYDRUS-2D model and simulation of soil moisture pattern in transplanting sugar beet with and without mulch under tape irrigation

This study aimed to calibrate the HYDRUS-2D model for simulating soil moisture distribution under tape irrigation in transplanting sugar beet, with and without mulching. The research was carried out during the cropping seasons 2017-2018 in 14 plots (7 plots with mulch and 7 plots without mulch) with 2 rows of 40x50 tape. To monitor soil moisture distribution, soil samples were collected from 12 plots, and access tubes of the PR2 device were installed at depths of 10, 20, 30, 40, 60, and 100 cm in two plots. The PR2 device was calibrated for a 7- day irrigation frequency and 6 irrigations. The calibration results showed that the default parameters a0=1.6 and a1=8.4 proposed by the PR2 manufacturing company were not appropriate for the loam-textured soil of the study area. For this research, a0 and a1 were modified to 1.8 and 8.3 for soil water contents higher than the filed capacity and to 1.2 and 8.6 for soil water contents lower than the field capacity, respectively. The PR2 device was then used to measure soil moisture contents for five irrigations (6 hours each irrigation), during and after irrigation until the next irrigation. The results showed that the HYDRUS-2D model performs appropriately in simulating soil water content in five irrigation intervals with and without mulch application. The mean absolute value of error (MAE) was less than 0.035, root mean square error (RMSE) was less than 0.042; correlation coefficient (R) was above 70%, and the sum of squared error (SSQ) was less than 0.41 percent. If the hydraulic parameters of the soil were recalibrated for the use of mulch, the HYDRUS-2D model provided the same efficiency. Therefore, the HYDRUS-2D model is recommended for designing and managing tape irrigation due to its good simulation during and after irrigation.