Influencia de la fertilización nitrogenada en el crecimiento y la producción del olivo y en la maduración de la aceituna

The aim of this work was to investigate the influence of nitrogen levels and application method on olive trees (Olea europea L.) growth and fruit maturation process. This study was done with full bearing Picual olive tress growing in Cabra, a locality of Cordoba province, Southern Spain, in non-irrigated and non-tillage conditions. In the course of a long-term experiment, those trees were subjected to annual applications of N (urea to the soil, foliar application). As July leaf analysis showed differences among leaf nitrogen concentration, the 12 trees with more extreme values of nitrogen (the most deficient 6 and the most well-nourished 6) were selected in order to investigate the fruit maturation process, according to the high or low leaf nitrogen content. Data of fruit colour and weight, oil yield evaluation and phenolic profiling were recorded throughout he fruit maturation process. On the other hand, for the entire plot, growth parameters such as yield, fruit size, ripeness index, pulp/stone ration, oil yield and vegetative growth were recorded to evaluate both the effects of different nitrogen amounts applied and application method on the olive tree development, which were statistically analyzed afterwards. The application method did not affect significantly any of these parameters. Nevertheless, applying increasing amounts of nitrogen resulted in an increase of leaf nitrogen concentration. In addition, the trees that received larger amounts of nitrogen did not show an increase in yield or vegetative growth, but the maturation process was delayed. Furthermore, fruit size, pulp/stone ratio and oil yield were reduced in trees that received higher amounts of nitrogen compared with the trees that received lower levels of nitrogen. These results suggest that nitrogen excess negatively affect the olive tree development and the fruit maturation process. In addition, the anthocyanins content was also negatively affected by the excess of nitrogen, contributing to the ripening delay. Consequently, nitrogen should be applied only when the previous season’s leaf analysis indicates that leaf nitrogen concentration is below the deficiency threshold (1,4 per cent) in order to optimize nitrogen fertilization in olive orchards and to reduce its losses by leaching and pollution