Application of olive mill wastewater to a Cretan olive orchard: Effects on soil properties, plant performance and the environment

The application of fresh olive mill wastewater (OMW) to the soil surface of an olive (Olea europaea, L.) orchard was studied as a low cost alternative method for the disposal of this waste. OMW were applied to a Cretan orchard with 20-year-old trees (cv. ‘Kalamata’) during winter time for 3 consecutive years, at a maximum annual rate of 420 m3 ha−1. The effects on soil properties and composition (pH, EC, N, P, K, organic matter and phenolic content), yield, photosynthesis and nutritional status of the trees were studied. In a separate experiment, the possibility for groundwater pollution was studied in large lysimeters (60 m3 of soil volume). The most important effects on soil composition included a significant increase on availability of K, which enhanced soil fertility, and an increase of phenolic compounds in the OMW-treated soil. However, phenols decomposed rapidly and no accumulation trend was observed after subsequent applications. No other negative effects on soil properties and plant behavior were observed throughout the experimental period, while the composition of drainage water at a soil depth of 2 m was not altered by the application of OMW. Based on the dosage used, the cost for adopting the method was estimated to less than €0.007 kg−1 of processed olive fruit.