Effect of Combined Salinity and Water Stress on Tomato Yield in Soilless Culture

Almost all districts of the country are experiencing quantitative and qualitative decline of agricultural water resources. Considering the extensive expansion of greenhouse cultivation and importance of tomato production, and in order to evaluate the combined effect of salinity and drought stress on growth and yield of tomato plant (Lycopersiconesculentum Mill. Cv. Oriental), four levels of irrigation (125% ETc, 100% ETc, 75% ETc and 50% ETc) and six levels of salinity (0.1, 1.3, 3, 5, 7 and 9 dS/m) were factorially combined in a completely randomized design with 3 replication in a greenhouse soilless culture. Yield and its indexes were measured during the crop growing season. As expected, results indicated that salinity of the nutrient solution and drought stress had significant negative effects on yield and growth indexes of plant. Yield data were fitted on different production functions (simple linear, logarithmic linear, quadratic, and transcendental). The results indicated that the simple linear form was the optimum form. The S1W4 treatment (EC= 0.1 dS/m, and 50% ETc) with 34.6 kg/m3 and S5W1 treatment (EC= 7 dS/m, and 125% ETc) with 6.4 kg/m3 had the highest and lowest water use efficiency, respectively. The iso-yield curves showed that by increasing irrigation water amounts, water with higher salinity can be applied without changing the yield.