Long-term field evaluation of the changes in fruit and olive oil chemical compositions after agronomic application of olive mill wastewater with rock phosphate.

The objectives of this study were to determine the long-term effects of agronomic application of olive mill wastewater (OMW) with rock phosphate (RP) in a field of olive trees, on olive fruits and oil quality. The results revealed that olive fruits of OMW-RP amended plants had higher contents of polyphenols and mannitol indicating that agronomic application of OMW with RP generated an oxidative stress. Land spreading of OMW with RP altered the relative proportions of individual sugars in leaves and fruits. Consequently, the oil content decreased significantly, and a marked decrease in the contents of carotenoids and chlorophylls was also observed. Changes also took place in the composition of fatty acids, particularly by the increase of linoleic acid and the decrease of oleic acid. Our results suggested that the use of OMW in combination with RP is expected to have a major negative impact on olive fruit and oil quality.