The Use of HYDRUS-1D to Study Impact of Irrigation Water Composition and Evaporation on Soil Hydraulics

Abstract

There is an increasing application of modelling software to develop a greater understanding of the soil process and determine the most appropriate soil irrigation regimes to promote crop growth. If the use of modelling software for this application is successful, then the model simulations must be accurate and generate simulation outputs that are concurrent with the real-world scenario. This research focused on the investigation of a simulation of an agricultural soil under a saline irrigation regime. The purpose of the study was to identify whether the model simulation could be utilised to assess the influence of saline irrigation on evaporation and soil hydraulic properties. The modelling software package, which was selected, was the HYDRUS-1D software. This is a publicly available software package that has been used extensively to simulate agricultural soils. An equilibrium flow model was selected based on Richard’s equation and the chemical model for the transport of soil solutes was based on an advective-dispersive one-dimensional transport model. The transport of soil solutes is essential due to the cation exchange process of calcium (Ca2+) and sodium (Na+) within the soil. It was assumed that solute transport occurs only within the liquid phase and that liquid and solid solute interactions are instantaneous. It was found that the HYDRUS-1D simulations were able to accurately model changes in water flow and solute transport within the soil profile. There was an evident influence of irrigation with saline water on the evaporation, water flow and solute transport in the soil profile. The findings indicate that this is likely to have occurred due to the influence of salinity of the soil's physical properties, causing aggregate swelling, dispersion and slaking. Thus, the soil hydraulic properties were suggested to be adversely impacted by the use of saline irrigation waters. The HYDRUS-1D simulation also suggests that saline water irrigation's effects continue even when the irrigation with saline water is ceased. It was only after repeated incidents of freshwater applications that the soil water flow and soil process began to return towards the soil conditions at the start of the simulation. The findings of this study have important implications for the use of HYDRUS-1D as an approach to understanding the effects of irrigation on agricultural soil and the use of this modelling software to develop irrigation regimes.