Effect of Plant Density on Artemisia annua L. Biomass and Essential Oil Yield and Its Weed Seed Germination Suppression

During spring-summer 2023 and 2024, an Artemisia annua crop was carried out, using two planting densities (20D = 5.0 plants m-2; 40D = 2.5 plants m-2). Morphological traits were measured, including height, stem number, diameter, weight, and dry above-ground biomass. The aerial parts were hydro-distilled, and the essential oil (EO) yield increased from the 1st to 2nd year, from 0.117 to 0.439% for 20D and from 0.157 to 0.550% for 40D. There were significant variations in chemical composition between the years, with an increase in the presence of oxygenated monoterpenes in the 2nd year and the disappearance of oxygenated sesquiterpenes. In the 1st year, sesquiterpene hydrocarbons were the main class, while in the 2nd, oxygenated monoterpenes predominated. The main components were artemisia ketone (8.05-65.77%), eucalyptol (4.70-13.14%), and beta-selinene (5.38-37.53%), present in all the EOs, and trans-caryophyllene (11.65%), present only in the 1st year EOs. The possible phytotoxicity of the EOs on seeds of plants found in the A. annua crops was evaluated. The most susceptible seeds were Sinapis alba, Papaver rhoeas, and Portulaca oleracea. The phytotoxicity was greater in the 2nd year, with more marked effects on the germination of P. rhoeas and P. oleracea (up to 100%). The inhibition of root elongation reached 100% for those at the higher concentrations tested.