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Title: Analytical steady-state solutions for water-limited cropping systems using saline irrigation water

item Skaggs, Todd
item Anderson, Raymond - Ray
item Corwin, Dennis
item Suarez, Donald

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2014
Publication Date: 12/26/2014
Citation: Skaggs, T.H., Anderson, R.G., Corwin, D.L., Suarez, D.L. 2014. Analytical steady-state solutions for water-limited cropping systems using saline irrigation water. Water Resources Research. 50(12):9656–9674. doi: 10.1002/2014WR016058.

Interpretive Summary: Maintaining the productivity of irrigated croplands in arid and semi-arid regions requires water management practices that prevent excessive accumulation of harmful salts in the root zone. Traditional guidelines for managing salinity and irrigation were mostly designed with the goal of maintaining root zone salinity at a level that avoids any reductions in crop growth or yield. Yet achieving maximum yield is frequently not optimal with respect to either grower profits or environmental conservation, particularly when water resources are limited. Since the availability of good quality water for irrigation is decreasing in many parts of the world, there is a growing need for management tools that can target submaximal yields and support the use of lower quality (saline) irrigation waters. In this work, we developed new mathematical models that can aid in the management of irrigation under water-limited conditions. Whereas classical guidelines can assist only in determining the amount of irrigation water needed to obtain maximum yields, the new research permits an analysis of expected yields when irrigation rates are lower and water quality is potentially poor. This research will help growers, extension specialists, and researchers seeking to manage irrigated agriculture under water-limited conditions.

Technical Abstract: Due to the diminishing availability of good quality water for irrigation, it is increasingly important that irrigation and salinity management tools be able to target submaximal crop yields and support the use of marginal quality waters. In this work, we present a steady-state irrigated systems modeling framework that accounts for reduced plant water uptake due to root zone salinity. Two new explicit, closed-form analytical solutions for the root zone solute concentration profile are obtained, corresponding to two alternative functional forms of the uptake reduction function. The solutions express a general relationship between irrigation water salinity, irrigation rate, crop salt tolerance, crop transpiration, and (using standard approximations) crop yield. Example applications are illustrated, including the calculation of irrigation requirements for obtaining targeted submaximal yields, and the generation of crop-water production functions for varying irrigation waters, irrigation rates, and crops. Model predictions are shown to be mostly consistent with existing models and available experimental data. Yet the new solutions possess clear advantages over available alternatives, including: (i) the new solutions were derived from a complete physical-mathematical description of the system, rather than based on an ad hoc formulation; (ii) the new analytical solutions are explicit and can be evaluated without iterative techniques; (iii) the solutions permit consideration of two common functional forms of salinity induced reductions in crop water uptake, rather than being tied to one particular representation; and (iv) the utilized modeling framework is compatible with leading transient-state numerical models.