Foliar application of biostimulants on olive oil quality

From the report “Effect of foliar application of amino acid, humic acid and fulvic acid on the oil content and quality of olive”, of Mohsen Miri Nargesi, Shahram Sedaghathoor & Davood Hashemabadi, published in Saudi Journal of Biological Sciences, 2022.

This study investigates the biochemical responses of three olive cultivars (‘Zard’, ‘Arbequina’, and ‘Manzanilla’) to foliar applications of amino acids (arginine, glutamine) and organic acids (humic and fulvic acids) under saline orchard conditions in Rudbar, Iran. The experiment followed a two‑factor factorial randomized complete block design with nine foliar treatments applied twice during the growing season.

The results show clear cultivar‑dependent differences: ‘Zard’ exhibited the highest Brix value, fruit protein content, carotenoids, anthocyanins, and phenolics, whereas ‘Arbequina’ produced the highest oil content. Organic acids and amino acids also produced distinct biochemical effects. Humic acid increased anthocyanins and phenolics more than other treatments, while arginine + humic acid and glutamine + humic acid produced the highest total chlorophyll levels. Glutamine alone significantly increased fruit protein content compared to other amino‑acid treatments.

Interaction effects between cultivar and treatment were particularly strong. ‘Arbequina × glutamine’ yielded the highest oil content, while ‘Manzanilla × fulvic acid’ and ‘Manzanilla × glutamine + fulvic acid’ produced the highest fruit protein levels. Antioxidant enzyme activities also varied: ‘Arbequina × arginine’ showed the highest SOD (superoxide dismutase) activity, and ‘Arbequina × glutamine + fulvic acid’ the highest POD (peroxidase) activity, indicating that amino‑acid and organic‑acid combinations modulate oxidative stress responses in a cultivar‑specific manner.

Overall, the study concludes that foliar application of organic and amino acids can significantly enhance oil content, pigments, phenolics, and antioxidant enzyme activity in olives, though the magnitude and direction of the response depend strongly on the cultivar and treatment combination. The most notable practical outcome is that ‘Arbequina’ produced the highest oil content when foliar‑sprayed with glutamine, highlighting the potential of targeted amino‑acid nutrition to improve oil yield under saline conditions.