Determining the Optimal Economical Threshold of Water Salinity to be Used in Cotton Irrigation (Case Study: Birjand Plain)

Salinity and water scarcity are tow main limitations on crop production in arid and semi-arid regions. This paper used sample field experimental yield data of cotton with three levels of irrigation water salinity, 2.2, 5.5 and 8.3 dS/m and four levels of irrigation amounts, 50, 75, 100 and 125 percents of cotton water requirements in Birjand. The best fitted production function was transcendental model with R2 equal 0.94. The purpose of this paper was to determine maximum salinity of irrigation water for Cotton. Results showed that maximum salinity of irrigation water is 8.6 dS/m on the condition that the price of saline water being equals to base price of fresh water in Birjand region.