2. Soil Salinity Modeling, Approaches, and Key Issues

Salinization is a progressive soil and water degradation process. Soil salinity can be natural or induced by human affecting aquifers and the most productive irrigated agroecosystems in arid and semiarid regions, representing an increasing environmental concern. Root zone soil salinity can be managed using advanced tools and adjusting irrigation application and using the concept of leaching requirement. Modeling the reactive transport in soil uses simplified representations of the reality, but can reveal complex interrelations of properties of the system under study, and is best suited for drawing scenarios for investigating “what-if…” questions. Each modeling effort tries to give answer to a particular question; hence, the input information required for running the models ranges in complexity as does the data acquisition efforts. The scale of application, geometry of the system, and biological, chemical, and physical processes represented, as well as the capability of representing an evolving system, are main differences among models. Some aspects important under normal agricultural practices are not well reproduced by some codes nowadays. Management practices, geometry of irrigation and evaporation, sinks of solutes (plant uptake), and interaction of fertilizers with soil components are incorporated in an uneven way in the available codes and should be further developed. Currently models become more and more mechanistic and require very intensive research efforts. There are uncertainties associated to the values of the input parameters, to the computation procedure, or to the inaccurate description of the system. The parameter estimation, analysis of sensitivity, and validation procedures are refinements applicable to most models. This chapter presents an overview of different modeling approaches, discusses the limits of application of models, and develops a study case.