Effect of nitrogen availability on olive oil quality

Nitrogen (N) is considered one of the major nutrients required for productive orchards. However, information regarding the effect of N on olive oil quality is scarce. We evaluated the relationship between olive tree nutritional status and major oil quality parameters using three experimental setups having different approaches: controlled trial, field trial and survey. In the controlled experiment, trees grown in inert media were exposed to eight levels of N. We found that oil phenolic content decreased linearly as a function of increased leaf N concentration, indicating protein-phenol competition. Free fatty acids (FFAs) increased with increased levels of fruit N concentration. The field experiment confirmed the finding that increased leaf N resulted in increased FFAs and reduced polyphenols. Finally, a survey of 25 commercial olive orchards found correlation between high N concentration in fruit and oil acidity. In conclusion, the findings regarding the negative effects of excess N suggest that balanced controlled fertilization is necessary to obtain high yields without harming olive oil quality.