Salt and Water Dynamics Under Saline Irrigation: Modeling Approaches

Worldwide efforts have been largely made to generate experimental information regarding water quality impacts on soils and crops, practices to control salt balances, and those to mitigate the damaging effects of salinity/sodicity. However, these field and laboratory investigations continue to be very laborious, time-consuming, and expensive. Therefore, several user-friendly computer simulation models have been put forward for predicting the dynamics of salts, changes in solute composition due to chemical interactions, the effects of these changes on water transmission characteristics of soils vis-a-vis root water uptake, and, ultimately, the performance of crops under such soil environments. These models comprise either steady-state or transient-state solutions. Former use simple representations of crops and soils, and assume that salt concentrations and soil-water contents are constant with time at a given point. The transient-state analytical solutions do account for the time-varying soil water dynamics under the varied irrigation and agro-climatic conditions and ultimately their impact on crop performance. Among these models, various versions of HYDRUS and SALTMED have more generic applications at the field scale. Though the requirements of expertise to handle and a large number of input parameters continue to be constraints in the large-scale adoption of analytical models, these allow for predicting dynamics of salinity and sodicity in root zones under variable irrigation, rainfall, and climatic conditions. Some of the most significant applications of these models in resolving issues related to leaching requirements, saline irrigation strategies and conjunctive use, drip irrigation, and predicting sodicity impacts are elaborated.