Effects of zinc nanofertilizer and salicylic acid on yield and yield components of fennel (Foeniculum vulgare Mill.) under drought stress conditions

To investigate the effects of different levels of drought stress, and foliar application of zinc nanofertilizer and salicylic acid on the yield and yield components of fennel (Foeniculum vulgare Mill.), a split-plot factorial experiment was conducted in a randomized complete block design with three replications in the village of Sultanabad, Razan city in Hamadan province in two years, 2018 and 2019. The main factor included the irrigation regime at three levels of irrigation after 50 (no stress), 75 (moderate stress), and 100 (severe stress) mm evaporation from Class A evaporation pan and the sub-factors consisted of foliar application of zinc nanofertilizer at two levels (without fertilizer and zinc nanofertilizer spray) and salicylic acid at four levels (0, 2, 4, and 6 mM). The drought stress decreased the number of umbels per plant, number of umbellules per umbel, number of seeds per umbellule, 1000-seed weight, and grain yield and increased the percentage of essential oil. The highest number of umbellules per umbel was obtained in the severe drought stress treatment with the application of zinc nanofertilizer and salicylic acid with a concentration of 4 mM. The application of zinc nanofertilizer under no stress, moderate, and severe drought conditions increased the grain yield by 14, 5.3, and 4.5%, and the essential oil content by 6, 2.9, and 9.9%, respectively. The concentration of 6 mM salicylic acid had the highest essential oil percentage (2.8%).