Effect of Protein Hydrolysates on Yield and Chemical Parameters of Oregano Cultivated Under Rainfed Conditions in Mediterranean Environments

A critical challenge for modern agriculture is the adoption of sustainable and effective strategies, also in the medicinal and aromatic plant (MAP) sector. In many areas, MAP cultivation remains dependent on traditional farming systems, with a lack of innovative techniques. This study investigates the effect of the foliar application of two protein hydrolysates, one animal-derived (PH 1) and one plant-derived (PH 2), on oregano (Origanum vulgare L.) cultivated under rainfed conditions in a representative area of Sicily (Italy). The aim was to evaluate whether these types of biostimulants could enhance production yield compared to untreated plants. Results showed that both protein hydrolysates induced significant improvement of the agronomic responses compared to the control. Specifically, treatments stimulated a substantial enhancement in fresh biomass (increases from 1.9 to 6.5 t ha−1) and dry biomass (increases from 0.9 to 2.4 t ha−1). Total phenolics and antioxidant activity decreased by 15–24% and 7–15%, respectively, compared to control plants during the two years. However, the aromatic profile of the essential oils was not significantly affected by foliar application of the two protein hydrolysates. The use of these foliar biostimulants represents a sustainable and highly effective strategy to maximize productive parameters while maintaining the chemical stability required by the market, offering a significant contribution to the optimization of oregano cultivation.