Seaweed extract and fulvic acid application affect the biomass performance, the essential oil yield and composition of Sicilian oregano grown in an organic agricultural system

Origanum vulgare ssp. hirtum is one of the taxa used as 'oregano' and is medicinal and aromatic plant (MAP) utilized worldwide in various sectors. Nowadays, agricultural systems are moving towards sustainable, organic, and environmentally friendly agricultural production and biostimulants have been used in recent years as a potential strategy. The objective of this research was to investigate the influence of seaweed extract based on Aschophyllum nodosum (AN) and fulvic acid (FA), applied with two different doses, on morphological parameters, fresh and dry yield, essential oil (EO) traits, total phenolic content (TPC), antioxidant activity (AA) and rosmarinic acid content (RAC) of organic oregano. Two-year experiment was conducted using a randomized complete block design with one main factor (foliar biostimulant) and 3 replicates. In AN- and FA-treated plants, increases in fresh biomass between 0.3 and 8.4 t ha- 1 and in dry biomass between 0.5 and 3.0 t ha- 1 were observed. The application of the lowest doses of fulvic acid (FA4) produced the highest EO contents (3.49 % and 3.46 %) and EO yields (73.3 and 97.4 kg ha- 1) in both years. The application of the lowest doses of FA produced an increase (on average 4 %) in thymol content. Biostimulant application generated contrasting response, and, in some cases, a reduction in some chemical parameters compared with control plants. The findings of this study contribute to add novelty in cultivation of oregano. The application of low doses of AN and FA allows to increase yields and improve some qualities of the secondary metabolites from organic oregano.