Investigation of different irrigation methods on plants is necessary due to limited water resources and the increasing need for food products. The purpose of this study was to evaluate the effect of sprinkler and drip irrigation systems and hormones on morphological and physiological characteristics of potato. Treatments included sprinkler and drip irrigation systems and hormones (gibberellic acid, acetylsalicylic acid, epi- brassinolide, and no use of growth regulators) as split plot based on randomized complete block design with three replications during 2015 and 2016 growing seasons at a research farm located in Malayer. Results showed that the highest level of tuber dry matter (TDM) was related to epi-brassinolide hormone + drip irrigation after using 80% of the field capacity (FC) in 2015 and epi-brassinolide hormone + drip irrigation after using 70% of the FC in 2016. The lowest amount of water use efficiency (WUE) was seen in sprinkler irrigation + no use of regulators in both years. The highest value of WUE was seen in epi-brassinolide hormone along with drip irrigation after using 80% the FC and drip irrigation after using 70% of the FC in 2015 and also in epi-brassinolide hormone + drip irrigation after using 70% of the FC in 2016. There were high and significant correlations between water use efficiency and relative water content with morphological characteristics. In order to increase the production and potato water use efficiency in cold dry climate, drip irrigation along with epi-brassinolide hormone is recommended.
