Mitigating drought stress by plant-derived biostimulant in Arbequina olive (Olea europeae L.) cultivar conducted in super high density

The climate change has negative effects on crop production worldwide. The scarcity of water in semi-arid zones proper the use of biostimulants to improve yield and quality parameters. The present work evaluated the impact of exogenous spraying with moringa leaves aqueous extract (MLE 5%) on agro-physiological behavior of the olive cultivar “Arbequina” conducted in super high density during two growing seasons (2019–2020). The experiment consisted of six treatments (T0 = 100% ETc; T1 = 100% ETc + 5% MLE; T2 = 75% ETc; T3 = 75% ETc + 5% MLE; T4 = 50% ETc; and T5 = 50% ETc + 5% MLE). Twelve trees were considered for each treatment and distilled water was applied as control for the MLE treatment. Vegetative growth, yield, water status, antioxidants, oil parameters, leaf gas exchange, and chlorophyll fluorescence were analyzed. Results showed that the net photosynthesis (Pn), stomatal conductance (gs), and evapotranspiration (E) varied significantly in response to drought stress and MLE treatments. The two water regimes (100% and 75% ETc) showed similar behavior regarding the agro-physiological responses to the applied treatments, whereas the 50% ETc water regime significantly affected the studied parameters. The MLE was effective in mitigating the water stress on olive trees, by improving vegetative growth, yield, photosynthesis, and water productivity. It appears that trees grown under 75% ETc water regime were more responsive to 5% MLE, as they exhibit the highest yield (8.4 kg/tree), oil content (28.3%), and water use efficiency, whereas 25% of irrigation water was saved.