Effects of harvest stage and diurnal variability on yield and essential oil content in Mentha x piperita L.

This study aimed at investigating the effect of ontogenetic and diurnal variability on yield and quality criteria of Mentha piperita. The research was conducted in the Ordu province of Turkey for two years. The trial was established in a randomised complete block design with 3 replications according to factorial regulations. Four different harvesting periods (budding, first flowering, 50% flowering, 100% flowering) and three harvesting hours (9:00 a.m., 1:00 p.m., 5:00 p.m.) were evaluated. A significant difference was determined between the trial years in all characters examined: plant height 55.9--69.0 cm, fresh herb yield 3 236--16 438 kg/ha, drug-herb yield 1 748--2 862 kg/ha, fresh leaf yield 3 477--4 506 kg/ha, drug leaf yield 968--1 253 kg/ha, essential oil ratio 2.0--2.5% and essential oil yield that varied between 19--28 L/ha. The highest yields were obtained at the beginning of flowering in drug leaf yield and 100% flowering period for all other characteristics. Diurnal variability was statistically significant only in the rate of essential oil, and the highest rate occurred in the 9:00 a.m. harvest. [ABSTRACT FROM AUTHOR]