Development of an olive phenological model in relation to air temperature

The effect of air temperature on olive phenological development has not been extensively studied. Indirectly related data are available, mostly from air pollen concentration measurements rather than direct observation of phenological stages. Data on phenological stages of olive collected in Sicily, by the Sicilian Agrometeorological Service (SIAS), in 10 locations characterized by different climatic conditions were used to develop and calibrate a phenological model for the most important developmental stages in olive. Phenological stages under study were: bud break, inflorescence emission, and full bloom A base-temperature linear model was developed by choosing a temperature threshold using as optimization criteria the Mean Bias Error (MBE) and the R2 of the relationship between observed vs. predicted phenological stage dates. A model with base temperature of 12°C was found to be the best predictor for all initial phenological stages. A more detailed analysis within each single phase showed a decreasing performance compared to predictions performed on the whole period (January 1st to full bloom). Highest displacements of model predictions from observed values occurred starting from bloom, whereas bud-break predictions had the best fit, with lowest residuals. This difference in the predicting ability of the model in different phenological stages could be ascribed to the stronger limitations by low temperatures that can occur early in the season, as for bud-break stage.