A dynamic simulation approach to soil salinity and sodicity control

Soil salinity and sodicity are twin problems potentially affecting soil fertility, farmers’ livelihoods and food security. Management and control of these problems, particularly on irrigated farmlands require knowledge and expertise crafted through appropriate models and experiments. The accumulation of salts on the soil profiles may occur through natural processes (of weathering of soil minerals, saline groundwater intrusion), as well as by human actions, that are mostly related to poor agricultural and irrigation practices. While accumulation of salt in soil water impedes crop evapotranspiration, sodicity (abundance of sodium cations among others) threatens the soil structure and degrades its hydraulic qualities. These problems are more pervasive in arid and semi-arid regions, where inadequate precipitation rates compared to evapotranspiration limit leaching of salts and facilitates their accumulation in productive topsoil. Therefore, irrigation and agricultural practices are crucial in controlling these problems to avoid their undesired consequences.
We build a dynamic simulation model of salinization and sodification in soil layers so as to test the impact of alternative irrigation practices with respect to water quality, quantity and schedule, on soil fertility and farm yields. The model is developed based on the system dynamics methodology, providing a feedback rich understanding of hydraulic, solute, and crop processes. While the hydraulic flow is the driver of solute transport, salinity and sodicity influences the hydraulic flows through their impact on evapotranspiration and hydraulic conductivity. The crop growth and its demand for evapotranspiration at various stages of development is modeled, considering available moisture and the accumulation of salts in the rootzone. Moreover, the model investigates farmers’ response to salinity and sodicity through adoption of different irrigation practices and crop choices, so as to observe the long-term development of the problem under the conditions of adaptive management.
The model has a generic theoretical structure that benefits from soil physics to formulate the complex processes of hydraulic flows and solute transport. Model parameter values are selected as representative of the field conditions of Konya Plain in Turkey, which is a semi-arid region partially experiencing soil salinization problems. As a part of the research project entitled, “Soil Salinity and Sodicity Management by Sustainable Irrigation Practices in Konya Plain”, the Interdisciplinary Multi-Institutional Network, during model validation phase, we will utilize data from the soil experiments that are conducted by our research partners. These data will include, however will not be limited to the experimentally characterized porosity and hydraulic conductivity curves. Ultimately, the model will provide an experimental platform to manage and control soil salinity and sodicity under different environmental conditions and farmer responses.

Keywords: Soil Salinity, Soil Sodicity, System Dynamics, Irrigation, Agriculture

Acknowledgement: This work was supported by the Scientific and Technological Research Council of Turkey [Project Number: TUBITAK-118Y343]