determination of optimal field crops irrigation depth using swap model in salinity condition

abstract in this study, seven main field crops of the rudasht and abshar irrigation networks of esfahan (with 54,000 ha designed command area) such as wheat, barley, onion, sunflower, fodder mays and sugar beet were selected and swap model was calibrated by inverse modeling base on field experiments results in order to determine crop water salinity production functions. field experiments were conducted with effect of saline water with different irrigation managements on crop yield at research station of drainage and soil reclamation of rudasht during 1996 to 1998 and 2005 to 2007. in terms of insufficient field treatments and in order to fit proper crop yield production function, swap calibrated model was run for different quantity and quality levels of irrigation water. quadratic form of crop yield production function was calculated for 6 salinity levels of irrigation water include 1, 2, 4, 6, 8 and 10 ds/m and each crop. optimal irrigation depth in different condition include scarcity of water quantity, land quantity and water quantity and quality was calculated base on crop yield production function, cost production function and marketable price of each crop based on 2008 with respect to maximize net benefit. results of analysis showed that in scarcity of water quantity for 10000 m3 available water, maximum net benefit gain onion cultivation with 52.6×106 rials beside with 1.16 ha of area cultivation. in land scarcity condition for specified available water, maximum net benefit gain onion cultivation, too. in scarcity of water quantity and quality condition, with increasing salinity of irrigation water, for 10000 m3 available water salinity level of irrigation water equal 2 ds/m, maximum net benefit gain onion cultivation with 35.11×106 rials beside with 1.44 ha of area cultivation, too. in salinity level equal 6 ds/m, maximum net benefit gain wheat cultivation with 18.37×106 rials and next maximum net benefit barely cultivation with 13.9×106 rials. yield of onion and fodder maize decreased severely so that for higher than salinity level of irrigation water equal 6 ds/m, net benefit was negative. in salinity level equal 10 ds/m, maximum net benefit gain barely and next sugar beet cultivation.