EFFECT OF NITROGEN FERTILIZATION ON FRUIT MATURATION OF OLIVE TREES

Excessive application of nitrogen is common in olive orchards and cause adverse effects on the soil and on the trees. In this work, the influence of the nitrogen status of the olive trees on fruit maturation was investigated. For this purpose, ‘Picual’ olive trees growing in Cabra, a locality of Córdoba province, southern Spain, were selected from a long-term experiment where the trees were subjected to annual applications of 0, 0.12, 0.25, 0.5 or 1.0 kg N per tree from 1993. In 2010, twelve trees were selected based on their leaf nitrogen concentration in July’s samples. Six experimental trees with less than 1.4% concentration of leaf nitrogen, established as the deficiency threshold, and six trees with more than 1.7% of concentration of leaf nitrogen, representing an excessive level, were selected for the experiment. Fruit maturation was delayed in trees with higher nitrogen levels. In this study, anthocyanin, a pigment responsible for the black color of olive fruits, was detected: cyanidin-3 rutinoside. This compound increased during maturation, but high content of nitrogen caused a reduction in anthocyanin. Also, in trees with higher nitrogen levels, oil content was lower compared with trees with leaf nitrogen concentration below 1.4%, indicating that lipogenesis was also delayed with high nitrogen content along the maturation period.