Application and Evaluation of the SWAP Model for Simulating Water and Solute Transport in a Cracking Clay Soil

Abstract

In Sicily, the increasing scarcity of quality water is leading to irrigation with saline water in soils having a considerable susceptibility to cracking. Irrigation systems involving high application rates are used in these irrigated areas, and bypass flow during irrigation is thus prevalent. Adoption of management practices accounting for cracking is therefore necessary to prevent salinization and land degradation. In this paper, water flow and solute transport in a Sicilian cracking soil irrigated with saline water was simulated by using the soil‐water‐atmosphere‐plant environment (SWAP) model, and the simulated results compared with measured values of soil moisture and salinity. The soil hydraulic parameters were obtained by inverse method based on multi‐step outflow experiments, adopting two different sets of hydraulic parameters/functions, that is, (i) the van Genuchten‐Mualem, (VGM model) and (ii) the Brutsaert retention equation coupled with the hydraulic conductivity model proposed by Gardner (B‐G model). The results obtained using field measurements from four soil profiles of a cracking clay soil showed that SWAP provided accurate predictions of water content, θ, when the soil hydraulic properties were expressed according to the B‐G model. Using the B‐G hydraulic parameters/functions, the model was calibrated with reference to the dispersivity (Ldis). A calibration value of about 20 cm was found for the four different profiles. In the conditions occurring in the Sicilian area where we are focusing our attention, the predictive errors associated with the simulated ECsat, can be considered acceptable if the purpose of application is to predict the influence of salinity on crop yield.