Effect on the physicochemical and lipid quality of alternative fertigation with micronized calcium sulphate in olive cultivation

Gypsum (CaSO₄•2H₂O) is a natural fertilizer used worldwide, which can improve the quality of horticultural crops and soils, and is certified for use in organic agriculture. The influence of fertilisation on olives and olive oil quality has not been suitably studied yet. This study evaluates the effect of fertigation with micronized (80-120 μm) CaSO₄ compared to the usual fertigation with Ca(NO₃)₂ on ‘Arbequina’ olive fruits and olive paste quality for two consecutive years. The quality parameters evaluated were weight, calibres, colour, firmness, soluble solids content, pH, acidity, moisture, total fat, and individual fatty acids. Representative subsectors of about 13 ha in a commercial super-intensive olive orchard were calcium fertigated with CaSO₄ or Ca(NO₃)₂. Freshly harvested olives were immediately used to obtain the olive paste in a commercial oil mill. Afterwards, the quality parameters of fresh fruits and olive paste from each fertilizer treatment were evaluated. In the two years, the quality of fruit and olive paste of both types of calcium fertigation, including the acidity and total fat content, were very similar. However, in terms of lipid composition, in the first year, the highest oleic acid content (68.4%) was reached in the olives fertigated with CaSO₄, while the highest linoleic acid content (13.8%) was found in the Ca(NO₃)₂ treated fruits in both years. Consequently, the ecological micronized CaSO₄ could be a good substitute for Ca(NO₃)₂ for calcium fertigation in sustainable cultivation practices of ‘Arbequina’ olive trees.