Nitrogen nutrition in olive orchards of Central Dalmatia

The aim of the present study was to investigate the effect of fertilization practices, especially with nitrogen (N), on N leaf status, fruit and oil yield, and oil quality parameters in orchards of Central Dalmatia. Questionnaires done by more than 100 olive growers revealed that fertilization practices vary widely. Based on the data obtained, 22 orchards with most prevailing practices in N application were selected for detailed soil, leaf and fruit analyses. The samples were taken from trees of the Oblica cultivar. N concentration in leaves averaged 1, 69% and ranged from 1.09 do 2.36% and correlated mainly with the intensity of agrotechnical prctices and fertilizer use expressed in the questionnaires. Based on results from 22 orchards, an additional subselection of 9 orchards with low, optimal nad high N leaf concentration was made. Hand-picked olives had on average 15, 5% of oil, fruit N concentration ranged from 0.43 to 0.71% ; with an average of 0.57%. The results showed correlation between N level in leaves and fruits, which was more pronounced in leaves with optimal N status. It was also found that N concentration in fruits was higher with lower K concentration in leaves. Significant negative correlation was found between N content in fruits and phenolic content in virgin olive oil, with increased N leading to sharp decrease in phenols in oil. As a basis for future studies on N nutrition in olive, fertilization experiment with three N supply levels was established on the cultivar Oblica.