SALINITY AND TRACE ELEMENTS ASSOCIATED WITH WATER REUSE IN IRRIGATED SYSTEMS: PROCESSES, SAMPLING PROTOCOLS, AND SITE-SPECIFIC MANAGEMENT
Location: Water Reuse and Remediation
Title: Modeling transient rootzone salinity (SWS Model)
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: September 1, 2011
Publication Date: January 2, 2012
Citation: Suarez, D.L. 2012. Modeling transient rootzone salinity (SWS Model). In : Wallender, W.W. and Tanji, K.K. (eds.) Agricultural Salinity Assessment and Management. ASCE Manual and Reports on Engineering Practice No. 71 (2nd Edition). ASCE, Reston, VA. Chapter 28 pp. 855-897.
Interpretive Summary: In the past years we have developed an increased understanding of the multiple processes (and their interactions) that impact plant production and stable soil conditions in irrigated agriculture in arid regions. Use of this information for management decisions can best be made using computer models that account for these processes. Soil salinity is often variable in time and space, hence transient salinity models are desirable for analysis of management decisions. The major processes to be included in these models are described. The Soil Water Salinity Model (SWS) model is applied to a number of field conditions and management decisions related to use of saline water in the presence of rain, irrigation with water elevated in boron concentration and reclamation of a saline sodic soil. The analyses can often be done with minimal site specific information. The application of the process based models allows for site specific recommendations and management plans. Use of the models is of interest to producers and irrigation specialists. It is expected that application of the models will result in improved crop production and more efficient use of available resources in salt affected irrigated regions.
The combined, water quality criteria for irrigation, water and ion processes in soils, and plant and soil response is sufficiently complex that adequate analysis requires computer models. Models for management are also needed but these models must consider that the input requirements must be reasonable, yet still provide adequate prediction of results. It is not practical for use of management models, to obtain detailed soil information and characterization of specific hydraulic and chemical characteristics for each soil. The SWS model considers the relevant processes of variably saturated water flow, carbon dioxide production and transport, cation exchange, precipitation and dissolution of soil minerals, B adsorption and desorption, as well as plant response including relative yield related to salinity and water stress. The model calculates potential evapotranspiration from climatic information predicts water consumption and makes use of default parameters and estimation of properties where practical. The Soil Water Salinity Model (SWS) model is applied to a number of field conditions and management decisions. Among the analyses are prediction of soil water content and carbon dioxide concentration throughout a cropping season and irrigation of saline, moderately sodic water in the presence of intermittent rain. We provide a management strategy related to leaching fraction when irrigating with water elevated in boron concentration above the toxic level and currently considered unsuitable for irrigation. It is demonstrated that high boron water can be used for up to a year if the soil has sufficient boron adsorption capacity. Other analyses shown include optimal use of water and amendment for reclamation of a saline sodic soil. As demonstrated, the analyses can often be done with minimal site specific information, requiring only generally known soil characteristics and water composition. The application of the process based models allows for site specific recommendations and management plans.