The effects of biostimulants on Lavandula angustifolia cultivation under insufficient irrigation.
Lavender, (Lavandula angustifolia Mill.; Lamiaceae) is a native species of the Mediterranean basin and has a wide range of medicinal uses and biological functions. The aqueous extracts, essential oils, and herbal formulations have long been utilized in traditional medicine, hygiene products, and cosmetics. The present study evaluated the effect of four different biostimulant products (Tr1: vegetable proteins + amino acids + 5% carboxylic acids; Tr2: vegetable proteins + amino acids + seaweed extracts; Tr3: 0,3% Stabilized Orthosilicic Acid; Tr4: 35% CaO and 35% SiO2 + Calcium Mobilization and Translocation Factor + 1% Mo, 15% Bo and 30% Zn; and the control treatment (Tr5: no biostimulants added) on field grown Lavandula angustifolia plants under three irrigation levels (I1: 164 , I2: 219 and I3: 274 mm). Lavender seedlings were transplanted in the field on April 2022, at the experimental farm of University of Thessaly, in Velestino, Greece. Each experimental plot included 15 plants and was replicated three times (n=3; 45 plants per treatment). Harvest took place on September 2022 by removing the antennas from each plant. All the antennas from the same plot were pooled in a batch sample for the quantification of essential oil yield with a Clevenger apparatus after air-drying at 42 °C. Our findings demonstrated that a decrease to the water supply (irrigation + precipitation) up to 16% and 31% resulted in a decrease of the fresh weight by 32% and 72%, respectively. Specifically, the fresh weight decreased from 1220 to 832 and to 338 kg ha-1 in the case of I3 to I2 and I1, respectively. Furthermore, irrigation has a considerable detrimental impact on the content of essential oils. Particularly, the highest irrigation dose (I3) resulted in a decrease in essential oil concentration compared to I1 treatment (from 1.86% to 0.99%). Additionally, a statistically significant difference amongst the tested biostimulants was discovered, with Tr4 emerging as the biostimulant with the higher essential oil yield (1.67%). In conclusion, our results indicate that deficit irrigation combined with biostimulants application is a sustainable tool that can ensure fresh biomass yield and high essential oil yield in lavender plants.