Cucumber is among the most important crops that is produced in greenhouse soilless culture across the world. Soilless culture is one of the effective method that improve crop yield and increase water use efficiency. Among the most important requirements for soilless system, are the appropriate substrate, suitable volume of nutrition and substrate lesching for salt equilibrium in the root zone. An investigation was carried out to identify the best combination of the substrate as well as the nutrition in greenhouse soilless culture for cucumber (cv. ‘Yalda’) at the hydroponic greenhouse of College of Agriculture, Isfahan University of Technology. In order to determine the best combination of substrate, different ratio of cocopit and perlit (0, 25, 50, 75 and 100 %) and different levels of nutrition (210, 425, 645, 935 and 1170 cc/day) were obtained and applied using completely randomized factorial design. Data were analyzed using SAS software and mean comparisons were carried out using Duncan method. Results of analysis of variance showed that effects of different substrate combinations was significant on leaching and electricity conductivity of substrate but not significant on yield and some other vegetative variables such as stem length, fresh and dry weight, dry matter percentage and acidity. The highest and the lowest amount of leaching was observed for 100 % perlit and 100% cocopit substrates, respectively. In other substrates, while the percent of perlite increased the leaching also increased. The electricity conductivity was significant in different substrate but there was no a distinct trend for various substrates. Effects of different irrigation levels was significant on vegetative variables, yield and electricity conductivity of substrate, and the highest amount of yield, fresh and dry weight, dry matter percentage and stem length was obtained at 1170 cc/day. Economical comparison of different levels of nutrient application showed that only the highest level of irrigation water (1170 cc/day) or nutrition application had economic justification. According to the results, for a soilless culture condition, a substrate of cocopit and perlite (1:1) and irrigation amount of 1170 cc/day are the most suitable substrate and irrigation level for greenhouse soilless culture of cucumber. Keywords : soilless culture, greenhouse, cocopit, perlite, irrigation levels, cucumber
