The total phenols in virgin olive oil are highly dependent on cultivar, but also on ripening stage and other agronomic factors. The focus of most studies on agronomic factors has been irrigation, while fertilization has received less attention. Most of the fertilization works find that nitrogen over-fertilization leads to a decrease in phenol contents in virgin olive oil (VOO) and extra virgin olive oil (EVOO), under rain-fed or irrigation management. Ortho-diphenols also decrease with high doses of nitrogen, with no effect on secoiridoids. Phosphorous has a minor effect on irrigated trees; while the role of potassium is controversial, with a lack of trials with calcium and micro-nutrients. Due to the great impact of the fertilization on the phenol content and quality of VOO, new research is necessary with focus aimed at different cultivars and agronomic factors.
The objective of this work was to evaluate the influence of irrigation and fertilization with nitrogen and potassium on the sterol and triterpene dialcohol contents in two trials of cv. Arbequina in super-intensive orchards in Madrid and Lleida (Spain), using a completely randomized block design. No significant differences in total sterols between deficit and full irrigation treatments were observed. Under very dry conditions, the sterol levels from fully irrigated trees were higher than from rain-fed treatments and the triterpene dialcohol erythrodiol+ uvaol content was lower in the irrigated treatments in Lleida. In the fertilizer trial with full irrigation, total sterols were higher in the two N treatments compared to the unfertilized one; while erythrodiol + uvaol decreased. The application of K fertilizer had no effect on total sterol or triterpene dialcohol contents. A proper fertilization and irrigation are vital to obtain high quality EVOOs that meet the regulatory range in sterol and erythrodiol + uvaol contents.
Regulated deficit irrigation in super-high-density (SHD) olive orchards is a well-known strategy to save water and control plant vigor, without decreasing fruit or oil yield. As there is controversial information about its influence on virgin olive oil quality, a trial was conducted in five SHD olive orchards of Arbequina cultivar in different locations of central, east, north and northeast Spain under full irrigation (FI) and regulated deficit irrigation (RDI) treatments. RDI applied during phase II of fruit growing (40% of total needs) saves more than 20% of water on average, without reductions in olive fruit or extra virgin olive oil (EVOO) yield. No threshold of 3.5 MPa of stem water potential was crossed in any case. RDI modified sterols and the fatty acid profile of EVOOs but not phenols, quality parameters, or the sensory profile. Latitude, altitude, and yearly rainfall have a big impact on some compounds such as campesterol, oleuropein, or margaroleic or linolenic acids.
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