Comparing the effect of different irrigation water scenarios on arid region pecan orchard using a system dynamics approach

Water scarcity and soil salinization in arid regions have made desalination a competitive alternative source for irrigation. Perceptions of a higher cost and other misconceptions about desalinated water have limited its broader usage in agriculture. In this study, we have focused on understanding the suitability of using desalinated water as a substitute for saline water in the pecan (Carya illinoinensis) orchards of southwest Texas. Pecan is a perennial high-value nut crop that cannot be easily replaced. Therefore, it represents a perfect case study for the application of desalinated water. A recently developed system dynamic model, SMITUV (System Dynamic Modeling of Infiltration, Solute Transport, and Root Water Uptake in Vadose Zone), was modified to assess the effects of irrigation with desalinated water when soil-water salt content increased above pecan tolerance levels. This model simulated five irrigation scenarios with different fractions of river water and saline groundwater. As expected, to sustain the same level of pecan production, a higher amount of desalinated water was needed with increasing amounts of groundwater in the irrigation mix. Soil texture had a significant influence on the amount of desalinated water required. For sandy and silty soils, the 100% river water scenario required no additional desalinated water. Clayey soils could not sustain high production even in a 100% river water scenario. An economic analysis showed that pecan operations might be viable in non-clayey regions for some irrigation mixture even after factoring in the cost of using desalinated water. However, current desalination techniques and associated costs were economically unviable for sustaining pecan in regions with saline groundwater and clayey soils. This study also demonstrated the application of SMITUV and system dynamic modeling as a decision-making tool to assist growers in understanding the farm-scale applicability of desalinated water.