The expected profitability to farmers from acquiring additional information on the biological response function of crop yield to soil-salinity is investigated. First, a switching regression approach to estimate piecewise linear response function with critical threshold level is presented. Then, an optimization irrigation model was developed, aimed at determining the optimal use of irrigation water for soil leaching. Finally, a loss function was defined, the expected value of sample information was calculated and the optimal number of additional needed observations was determined. At each stage, an empirical analysis, using data from potato field experiment in Israel, is presented.