Abstract
The use of organic acids and phenolic compounds that are present in olive mill wastewater (OMW) represents a new perspective in rock phosphate (RP) research and a possible solution for the recycling of the OMW. To test the hypothesis that OMW applied in combination with Gafsa RP to olive tree plants can affect P mobilisation from RP to olive trees, a field experiment was conducted to evaluate the potential use of OMW with RP as soil amendment on olive tree alkaline soils. Treatment included three levels of OMW and RP application: M0 (non-amended control), M1PN (30 m3 ha-1 of OMW+150 kg ha-1 of RP) and M2PN (60 m3 ha-1 of OMW+150 kg ha-1 of RP). Five years after the start of the experiment, the available phosphorus decreased significantly. Amended olive trees had lower rate of photosynthates compared to the control, mostly due to decreased sink demand for carbon by the root. The biomass of arbuscular mycorrhizal (AM) fungi and the development of colonisation in the olive tree roots decreased dramatically by the application of OMW and RP. Phenols accumulation in leaves was significantly higher in the OMW and RP amended soils, whereas total chlorophyll, chlorophyll a, and chlorophyll b in olive trees leaves decreased significantly after agronomic application of OMW and RP. Taken with data from experiments in field conditions, our results suggest that the use of OMW in combination with RP, in order to mobilise P from RP to olive trees, are expected to have a major negative impact on plant performance.
Highlights
The olive tree (Olea europaea L.) is the most important evergreen tree in Tunisia with 60 million olive trees covering 1.6 million hectares of land, where it is grown traditionally in rain-fed conditions [1]
To test the hypothesis that olive mill wastewater (OMW) applied in combination with Gafsa rock phosphate (RP) to olive tree plants can affect P mobilisation from RP to olive trees, a field experiment was conducted to evaluate the potential use of OMW with RP as soil amendment on olive tree alkaline soils
Phenols accumulation in leaves was significantly higher in the OMW and RP amended soils, whereas total chlorophyll, chlorophyll a, and chlorophyll b in olive trees leaves decreased significantly after agronomic application of OMW and RP
Summary
The olive tree (Olea europaea L.) is the most important evergreen tree in Tunisia with 60 million olive trees covering 1.6 million hectares of land, where it is grown traditionally in rain-fed conditions [1]. The annual olive oil production in the Mediterranean basin exceeds two million tones and the respective OMW co-produced may exceed 10 million tones. Water of good quality is used to irrigate crops more sensitive to water shortage [6,7]. In these conditions, the reuse of OMW may lead to higher and more consistent levels of olive production, minimizing the exploitation of fresh water resources
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