Effects of bio-fertilizers on some physiological characteristics, essential oil percentage and yield of spearmint (Mentha spicata L.) under deficit irrigation

Water scarcity adversely affects many physiological and metabolic processes of the plants. To study the effects of drought stress and fertilization on some physiological characteristics, essential oil percentage and yield of spearmint, a field experiment was conducted at the Research Farm of the College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran. The experiment was conducted in a split plot arrangement based on a randomized complete block design with three replications. Treatments included three irrigation treatments (100%, 75% and 50% of plant water requirement) as the main plot and four fertilizer regimes including no fertilizer (control), chemical fertilizer (N), bio-fertilizer (rhizome inoculation with Azotobacter, Pseudomonas and mycorrhiza) and integration of biological fertilizer and 50% chemical fertilizer as the sub-plot. The results showed that all traits measured were significantly affected by the main and interaction effects of deficit irrigation and fertilizer. The content of chlorophyll a, chlorophyll b, carotenoids, total chlorophyll, percentage and yield of essential oil and yield decreased with increasing water stress while the rate of carbohydrate and proline as well as the electrolyte leakage percentage increased. Furthermore, the results showed that under 100% and 75% irrigation systems, application of chemical and integrated fertilizers improved the physiological characteristics, yield and percentage and yield of essential oil. Under 50% irrigation regime, the best performance was related to bio fertilizer.