The effect of nitrogen overfertilization on olive tree growth and oil quality

Mature olive trees (Olea europaea L.) growing in the drylands in Southern Spain were fertilized annually with different amounts of nitrogen. After six years of experiment the results indicate that, under these conditions, increasing the amount of nitrogen applied from 0 to 1 kg of N per olive tree did not result in an increase of yield, fruit size, oil content or vegetative growth. However, olive oil characteristics such as polyphenol content, bitterness (K-225) and oil stability decreased when nitrogen was applied at the highest rates, affecting oil quality negatively. Leaf N concentration was always above the deficiency threshold of 1.4%, but varied among treatments. The results suggest that annual application of N fertilizer to olive orchards may provoke nitrogen overfertilization when leaf N is above the deficiency threshold.