Numerical simulations to estimate wetted soil volumes in subsurface drip irrigation¹

Simulações numéricas para estimar os volumes de solo molhado na irrigação por gotejamento subterrâneo

ABSTRACT

Water scarcity has become a concern for many countries; a proper irrigation system is essential for rational water use. Therefore, information on water dynamics within the wetted soil is necessary. Field investigations and laboratory analyses can measure wetted soil volume dimensions, but these are time-consuming and costly. Mathematical models can also be used to obtain such information based on soil physical-hydraulic properties, among the most used models in HYDRUS-2D. In this sense, we aimed to simulate water movement in a sandy soil profile using the HYDRUS-2D model for subsurface drippers at different spacings, depths, and flows rates. Initially, a greenhouse test was carried out to validate HYDRUS-2D for the soil Psamment (Ferralic Arenosol). After validation, simulations for drippers were arranged as follows: spacings of 0.30, 0.40, and 0.50 m; depths of 0.20, 0.25, and 0.30 m; and flow rates of 1.0 and 1.6 L h^-1. In all simulations, ten applications of 1 L of water were carried out.

Simulations showed that the dripper spacing, depth, and flow rate of 0.40 m, 0.20 m, and 1.6 L h^-1 presented the best performance. In this configuration, wetted soil volume remained at an adequate depth in a scenario of sugarcane root and near the surface, avoiding economic and environmental costs due to water losses to deeper soil layers.

Key words
Water content; HYDRUS-2D; Irrigation project; Mathematical model.