Influence of irrigation treatments on the yield and quality of 'Istrska belica' olive oil

In recent years, Slovenian olive growers and producers have faced problems in achieving constant yields and quality of olive oil due to extreme weather conditions, especially because of the more frequent occurrence of drought. A technically accomplished pilot automatic irrigation system for olive trees was established. In 2015, the impact of different irrigation treatments (0, 15, 33, 40 and 100% ETc (crop evapotranspiration)) on olive cultivar 'Istrska belica' were studied to determine the minimum amount of added water that has a positive effect on the yield and quality of the extra virgin olive oil produced. The study results showed that the quantity of applied water equal to 100% ETc had a significant effect on yield of olive fruits. The average fruit mass of the trees grown under full irrigation (100% ETc) was significantly higher than that of those given rain-fed and deficit irrigation treatments (15, 33 and 40% ETc), with no significant differences found between these treatments. The fatty acid contents showed the highest amount of oleic acid (75.61%) at 100% ETc and the lowest amount (74.69%) at 15% ETc, while the highest amount of linoleic acid (6.52%) was determined at 15% ETc and the lowest (5.98%) at 100% ETc. Total biophenol content and biophenol composition was determined. The 40% ETc irrigation system produced the highest amounts of total biophenols, total oleuropein and total ligstroside derivatives (1076, 562 and 388 mg kg(-1), respectively), while the lowest results (883, 477 and 299 mg kg(-1), respectively) were determined in the control system (0% ETc). The organoleptic assessment of the olive samples showed that the positive sensory attributes of fruity, bitter and pungent were more intensive at 33% ETc and were graded highest. Olive oil from non-irrigated trees (0% ETc) received the lowest sensory score.