Combined Sulfur and Nitrogen Foliar Application Increases Extra Virgin Olive Oil Quantity without Affecting Its Nutritional Quality

Abstract

This study investigates the effect of combined sulfur (S) and nitrogen (N) foliar fertilization on leaf S and N concentration, as well as on the growth of olive fruit and on the quantity and quality of olive oil, obtained from two olive cultivars ‘Istarska bjelica’ and ‘Leccino’ in two consecutive years. S and N are some of the most important nutrients, and both play a crucial role in plant oil production. The here-reported fertilization program significantly increased S concentration in leaves without affecting N concentration, which led to an increase in fruit yield and improvement of all fruit morphological parameters. The best oil yield per tree was obtained under the treatment with the highest S/N dose. Oil quality was not affected by S and N supply, and this allowed us to classify all our oil samples as extra virgin (EVOO). Regarding the content of total phenols (TPC) and composition of fatty acid methyl esters (FAME), they remained unaltered under the applied treatments. All investigated fruit morphological parameters, as well as fruit and oil yield, were highly cultivar-dependent. ‘Istarska bjelica’ was characterized as a cultivar with higher fruit mass and pulp percentage, while its stone parameters were lower than those of ‘Leccino’. Consequently, the extraction oil yield obtained from ‘Istarska bjelica’ fruits was much higher. Moreover, environmental conditions had a great impact on fruit and oil quantity. The here-obtained results led us to the conclusion that supply of S and N can enhance oil production without affecting its nutritional quality, a finding that could generate large long-term effects on economic growth in the olive oil sector.

Irrigation of Young Olives Grown on Reclaimed Karst Soil Increases Fruit Size, Weight and Oil Yield and Balances the Sensory Oil Profile

“…The fruits of the studied cultivar Oblica obtained in this study can be described as oval, with an average width of 1.93 cm and length of 2.14 cm ( Table 2 ). These values are similar to those obtained when describing the fruits of Istarska bjelica, while they are larger than the fruits of Leccino [ 30 ]. Although these parameters have been shown to be cultivar dependent [ 30 ], our results on the influence of irrigation on fruit size parameters are in agreement with previously published results [ 8 , 31 ].…”

Effect of Combined Sulfur and Nitrogen Foliar Supply on Olive Oil Volatile Compounds and Sensory Attributes

“…Concentration of macro-and micro-elements in Istarska bjelica and Leccino leaves, after foliar treatment with fertilizer containing S and N (0 mL SN, 7.5 mL SN, 15 mL SN, and 22.5 mL SN) that were collected in two consecutive years are reported in Table 1. As demonstrated in our previous report, the concentration of S was significantly higher in the leaves that were treated with 15 mL SN and 22.5 mL SN when compared to other two treatments, while no effect of the applied fertilizer on the N concentration was observed [29]. A higher concentration of S was found in Leccino leaves in 2020 when compared to all other combinations.…”

“…The concentration of S remained unchanged in Istarska bjelica leaves in both years. The Leccino leaves in 0 mL SN and 7.5 mL SN treatments were more abundant in N than Istarska bjelica leaves [29]. Treatment significantly affected the concentrations of Mg and manganese (Mn) with the lowest concentrations found at 22.5 mL SN when compared to all the other treatments.…”

“…All the experimental conditions, treatments, sampling, leaves' minerals concentration measurement, and oil extraction were described in detail in our previously published paper [29]. Briefly, a two-year field experiment was set up as a completely randomized design with two olive cultivars (Istarska Bjelica and Leccino) and four foliar fertilization treatments which were applied two times during the summer period in each experimental year.…”

“…The total rainfall was 881.5 mm in 2019 and 702.7 mm in 2020, respectively. The meteorological conditions are described in detail in our previous paper [29].…”