A Dynamic Analysis of Optimal Water Use under Saline Conditions

Abstract

Irrigation with saline waters is a major problem in many parts of the world. Economic questions have usually been addressed using synthesized production functions and theoretically based soil salinity relations. The purpose of this paper is to estimate functions relating crop yield and salt accumulation in the soil to initial soil salinity and water quantity and quality. Crop response functions and dynamic salt balance relations are estimated from experimental data for alfalfa and cotton. The estimated functions are then used in a dynamic programming model to determine optimal water applications for different levels of initial soil salinity and crop and water prices. Salinity is a severe problem for irrigated agriculture in many parts of the world. Farmers face economic questions such as optimal water applications for given irrigation water quality, reuse of drainage water, reduction in profits from using saline waters, and rate of mixing good with saline water. Answering these questions requires knowledge of crop-yield response to water quantity and quality. Because salt may accumulate in the soil over time, it is also necessary in many cases to consider the impact of current actions on future production. One common approach is to divide the overall system into two subsystems, water-soil and soil-crop yield. The water-soil relations are often treated using theoretically based models of water and salt transport in soils (Bresler; Childs and Hanks; Bresler, McNeal, and Carter). Crop yields are then estimated from the calculated salinity levels using experimentally determined relations, such as in Maas and Hoffman. Although this approach is potentially quite useful, the assumptions in