Farimah Omidi - PhD Scholar of Irrigation Science and Engineering; Tehran; Iran
Mehdi Homaee - Professor, Irrigation and Drainage Department, Agriculture and Natural Resources Campus, Tarbiat Modares University, Tehran, Iran

In most arid and semi-arid regions of the world, cultivation soils are saline due to droughts, lack of precipitation and irrigation with saline water. On the other hand, water scarcity and water and soil resources salinity have led farmers to apply chemical fertilizers in order to decrease the effect of water and salinity stresses and improve crop yield. In addition, water scarcity and its importance as an intermediate good, have increased water demand as an economic good. So, determining the irrigation water price when deficit irrigation along with chemical fertilizers is being applied to improve water productivity is of vital importance. For this purpose, green pepper (Capsicum Annum) was cultivated applying four irrigation, three salinity and three nitrogen treatments which were 120, 100, 70 and 50% of crop water requirement, 0.5, 2 and 4 (dS/m), 100, 70 and 50% of crop nitrogen requirement respectively. The crop yield was then collected and measured as dry matter at the end of the cultivation period. Crop-water-salinity-nitrogen production functions were derived and then irrigation water price was calculated in order to calculate irrigation efficiency and water productivity. The results indicated that increasing salinity in each irrigation treatment, decreased water price. Also, increasing salinity along with increasing nitrogen application decreased water price. But, water stress affected water price more than salinity stress and nitrogen treatments respectively. Regarding to the results, applying 50% of crop water requirement with the salinity of 0.5 to 2 (dSm⁄) and 100% of crop nitrogen requirement, maximized irrigation efficiency (IE). But, applying 70% of crop water requirement with the salinity of 0.5 to 2 (dSm⁄) and 100% of crop nitrogen requirement, maximized water use efficiency. Also, Physical, physical-economical and economical productivity decreased in all irrigation treatments when salinity increases. All the conducted results also indicated that the salinity threshold value is 2 (dSm⁄) for green pepper. In addition, to apply 100% of crop nitrogen requirement when deficit irrigation was implemented decreased crop yield and water productivity consequently.

Climate change, crop production functions, irrigation efficiency, economic productivity, simultaneous abiotic stresses