Environmental & Analytical Toxicology

Agronomic Application of Olive Mill Wastewater with Rock Phosphate Influence Soil Phosphorus Availability, Arbuscular Mycorrhizal Fungal Colonisation and Olive Tree Performance under Long-Term Field Conditions

Abstract

Beligh Mechri, Meriem Tekaya, Hechmi Cheheb, Mohamed Hammami and Faouzi Attia

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.