Shortage of water is the most important limiting factor for crop production in arid and semi-arid regions of Iran. Higher efficiencies for present water supply can be obtained by deficit irrigation. Seasonal and intra-seasonal approaches for deficit irrigation for Sorghum are compared in this study. The data for deficit irrigation were collected at the Bajgah area, a semi-arid region, located 16 km north of Shiraz, in southern Iran. Time pattern distribution of applied water was not considered in their seasonal approach and the cost-benefit ratio analysis are performed on an annual basis. Decision making in the intra-seasonal approach is based on water allocation at different growth stages of crops. The results showed that there are some differences between the two approaches as far as the optimal water reduction is concerned. Seasonal approach showed a constant water reduction (18%) irrespective of water cost variation, while the intra-seasonal method offered higher allowable water reduction of 23% for unit water cost of 10 Rls m^-3 which may lead to a more economical water use. However, the result obtained in the intra-seasonal method is sensitive becomes lower than that of seasonal approach at the higher unit water cost. These results confirmed a previous result on Corn about the differences for the two approaches. Meanwhile, there is a substantial difference between the results for Sorghum and Corn in two different approaches.

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