Subsurface irrigation system design for vegetable production using HYDRUS-2D

Abstract

In the subsurface irrigation management of extensively cropped vegetables, uniform crop growth requires the maintenance of uniform soil water suction at the root zone across a field. Moreover, a fixed value of suction that is suitable for crop growth should be maintained. However, accounting for the temporal and spatial changes in the suction is beyond human capability. Using HYDRUS-2D, this study modeled a spinach field in Tsukuba, Japan, which is irrigated by subsurface irrigation pipes. The subsurface pipes were located 55 cm below the soil surface. The pipes were placed 150 cm apart. Belt-shaped water shielding sheets were installed beneath the pipes. Irrigation was empirically managed. The measured physical soil properties of the spinach field were input into the model as initial values and then calibrated using the irrigation data and observed soil water suction across the field. The calibrated model was further verified by comparing the simulated and other observed suctions. After model verification, several scenarios were created by varying the given conditions: (1) the intervals of subsurface irrigation pipes, (2) the depths at which the irrigation pipes were located, (3) the existence of a water shielding sheet beneath the irrigation pipes, and (4) the shape of the water shielding sheet. These scenarios were compared, and the optimal scenario, which facilitates equal soil water suction that is close to the suction required for the growth of spinach, was selected.