Potential Use of Olive Mill Wastewater Spreading in Olive Orchards for Improving Soil Fertility and Olive Oil Quality Under Semi-Arid Environment

In Tunisia, olive growing and olive oil production represent a key element of the agricultural and economic sectors. Furthermore, olive producing areas are mostly located in semi-arid and arid regions with low water availability. On the other hand, olive oil industry generates high liquid effluent volumes (olive mill wastewater (OMW)) that represent a major environmental concern, and therefore must be appropriately managed. Accordingly, spreading OMW on agricultural lands in water scare areas may help to sustain dry lands productivity. In this study, we investigated the long-term effects of OMW spreading to an olive orchard in a semi-arid region. Physicochemical and biological properties of soil as well as olive oil quality were monitored. OMW was applied, after the end of the olive milling season, at annual dose of 50 m(3) ha(-1) y(-1) every 2 years. The findings revealed that the OMW application increased soil water content. Moreover, OMW positively affected soil fertility, and increased, soil organic matter and biological activity. The overall results of this study indicate that OMW spreading at doses of 50 m(3) ha(-1) y(-1) in a semi-arid region improves soil physicochemical properties and does not have a negative impact on olive oil quality. Additionally, direct spreading of OMW, if applied every 2 years, could be a sustainable practice in olive orchards under semi-arid environments.