Characterization of the nutritional status of olive (Olea europaea L.) orchards in the Verona area of Lake Garda and study of the effects of commercial products on the fruit set of Casaliva variety plants

The olive tree (Olea europaea L.) is one of the most widespread fruit trees in the Mediterranean basin, cultivated for the production of table olives, olive oil, and related products. In the Garda lake area olive cultivation has ancient roots, and the extra virgin olive oil produced in this region has been recognized as a Protected Designation of Origin (PDO) product since 1997, gaining considerable fame for its delicate and elegant characteristics. However, in recent olive-harvesting seasons in the Garda lake area, there have been some productivity problems whose exact causes are still unknown. Data from the Consortium for the protection of Garda PDO show that the biennial bearing, a typical phenomenon of this plant, has intensified over the last 5 olive-growing seasons, resulting in a significant loss of production for two consecutive seasons, almost reducing it to zero. This thesis aimed to analyse the nutritional status of six olive groves in the Garda lake area (Verona province) through soil and leaf analysis, followed by the evaluation and interpretation of the results to characterize their nutritional status. The results did highlight a potassium deficiency in the soil of Lazise, but the most interesting finding is related to the limited boron content in all six soils. Also, in all foliar analysis, an actual deficiency of boron was identified, typical of Garda lake olive groves (Bargioni, 1992), which, although characteristic, will need ongoing monitoring and more in-depth evaluation, possibly corrected through fertilization. In particular, in future studies, it would be very interesting to assess not only the availability of these nutrients but also their movement in the soil. Indeed, nutrient movement is primarily dependent on soil water content, which, in the present context of climate changes, can strongly influence the absorption process in the different plant organs and tissues. The olive tree is characterized by abundant flower production during the spring season, but with a reduced fruit set percentage. Furthermore, the number of fruits that reach maturity, i.e., the harvest, is lower than those initially present on the tree, due to physiological and non-physiological drop phenomena. In this thesis, field trials were conducted in two of the olive groves selected previously for the nutritional characterization, to assess whether the use of commercial products aimed at improving plant nutrition and condition could influence the fruit set percentage, ultimately increasing olive production. Two commercial products (a biostimulant and a fertilizer) were used in the experimentation to evaluate potential benefits on the fruit set percentage. Visual field counts of the number of flowers after anthesis and the number of fruits at different stages of fruit development were carried out. After processing the collected data, including through statistical analysis, it was found that there are no significant differences, in terms of final fruit set and the trend of the fruit set percentage, between treated and untreated groups in either of the two orchards. This study cannot definitively conclude whether the products used can increase the fruit set percentage. It is believed that the study should be repeated, and parameters for evaluation should be expanded to include the evaluation of additional production-related factors, not just fruit set. For example, differences in drupe size between treated and untreated groups or oil content in the drupe should be evaluated. Additionally, other factors influencing fruit set, such as climatic conditions and variety, should also be taken into account.