optimization of water use and determination of tomato sensitivity coefficients under combined salinity and drought stress in karaj

abstract different strategies are existed for adjusting with water shortage, of which the strategy of suitable policies adoption by determining optimum production function can be mentioned. water shortage and quality degradation of soil and water resources is one of main factors of production reduction. therefore, this study was carried out for determination of tomato sensitivity coefficients and its water-salinity-yield optimum function in karaj. the experiment was performed as a complete randomized design with three replicates including two factors; salinity and irrigation water. salinity and irrigation water factors consisted of four levels (s1=0.7, s2=4, s3=8 and s4=12 ds/m) and three levels (w1=100, w2=75 and w3=50 percent of water requirement), respectively. the soil texture was sandy loam. yield data were fitted on different forms production functions (simple linear, logarithmic linear, quadratic and transcendental) and the optimum one was determined after sensitivity analysis. then, the values of water use efficiency and plant sensitivity coefficients were determined. results of sensitivity analysis showed that the quadratic production function is optimal production and it can be recommended. investigation of the maximum values of error (me) showed that the logarithmic linear and simple linear functions have had the highest error. in the irrigation treatments, w1s1 (control) and w2s1 (75% of water requirement) with 7.57 and 7.5 kg /m3 respectively had the highest water use efficiency. however, water use efficiency decreases if the drought and salinity increases. the average value of ky, in the condition of combined salinity and drought stress was 1.696. moreover, plant sensitivity values (ks) decreases if salinity and drought increases and the lowest value of ks were belong to w3s4 (0.57). the iso-yield curve showed that by increasing of irrigation amounts, water with higher salinity can be applied without yield change.