Centre Bio: Biorefineries, Bioindustries and Bioproducts

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Moderate nitrogen rates applied to a rainfed olive grove seem to provide an interesting balance between variables associated with olive and oil quality

Publication . Silva, Ermelinda; Gonçalves, Alexandre; Martins, Sandra; Pinto, Luís; Rocha, Luís; Ferreira, Helena; Moutinho-Pereira, José; Rodrigues, M.A.; Correia, Carlos M.

Nitrogen (N) fertilization has been extensively studied all over the world, not only due to its impact on plant growth and yield, but also on product quality. Olive oil is a natural product highly valued by the markets, due to its role in the Mediterranean diet, but only when its quality is above legally established standards. Thus, it is important to continue to study how cropping practices can impact the quality of olive oil in order to fine-tune the guidelines issued to producers. The objective of the three-year study was to assess the effect of the application of 0, (N0), 40 (N40) and 120 (N120) kg ha-1 of N in a rainfed olive grove on variables associated with fruit biometry and the maturation index, polyphenols in olives and olive oil, the evolution of the quality of the oil over time and sensory analysis. The application of N prolonged the period of coloration, delaying the maturation of the fruits, particularly in the higher doses of N applied. N application changed the phenolic composition and the antioxidant capacity of the fruits and olive oil, but without a clear trend among years. In general, the high N rate negatively affected the quality of the oils, reducing the oxidative stability and bitterness of the oil when compared to N40 treatment; this is due to the lower content of phenolic compounds that have a radical scavenging capacity. Excessive N application (N120) increased the degradation of the oil quality, as it led to an increase in the K232 extinction coefficient. Moderate N rates (N40) seem to be a good compromise to guarantee the quality and stability of the oil, although there was some interference from other uncontrolled environmental variables; these were probably accentuated because the olives came from a rainfed olive grove. The sensory analysis panel detected a defect (winey-vinegary flavour) in the oil from N40 treatment that is difficult to justify and will need more attention in future studies.

2023Journal article

Open access

Olive yield and physicochemical properties of olives and oil in response to nutrient application under rainfed conditions

Publication . Silva, Ermelinda; Gonçalves, Alexandre; Martins, Sandra; Brito, Cátia; Ferreira, Helena; Ferreira, Luís M.M.; Moutinho-Pereira, José; Rodrigues, M.A.; Correia, Carlos M.

The effects of mineral fertilizers on the physicochemical properties of olives and oil under rainfed conditions is scarce. In this three-year study, the results of a nitrogen (N), phosphorus (P), potassium (K) and boron (B) fertilization trial carried out in a young rainfed olive grove and arranged as a nutrient omission trial are reported. The control consisted of the application of N, P, K and B (NPKB) and four other treatments corresponded to the removal of one of them (N0, P0, K0 and B0). Olive yield and several variables associated with the physicochemical properties of olives and oil were evaluated. The NPKB treatment increased olive yield compared to the treatment that did not receive N (N0). Although dependent on the climate conditions of the crop season, the NPKB treatment increased fruit weight and the pulp/pit ratio and its fruits tended to accumulate more oil than K0. However, the phenolics concentrations on fruits and oil tended to be lower. All olive oil samples were classified in the “extra virgin” category and all showed a decrease in its stability between 3 and 15 months of storage, regardless of treatment, especially in N0, P0 and B0 treatments. The results of the sensorial analysis indicate that all the oils fell into the medium fruitiness and greenly-fruity category. Only in P0 and B0 were defects detected, namely muddy sediment. Thus, this study seems to indicate the importance of N application, but also a balanced nutrient application and that further studies are needed, given the difficulty in finding clear trends in the response of measured variables to fertilizer treatments.

2023Journal article

Open access