Improvement of soil properties by application of olive oil waste

Abstract – Wet olive pomace isan organic lignocellulosic material, a by-product of the olive milling process, a typical and traditional activity in many Mediterranean countries. Wet olive pomace has difficult commercialization due to its high moisture content of 55–65%, that causes a noticeable increase in oil extraction costs. However, it could be conveniently reused in agriculture as a valid soil amendment to improve soil fertility and structure. Here, we studied the effects of the application of increasing amounts of non-fermented wet pomace on the fertility of a silty-clay soil, grown with3 crops in succession: sunflower-wheat-wheat. The experiments were conducted atthe Agricultural Faculty ofBari, Italy, on a Pachic Hoploxeroll soil characterized by illite and kaolinite and large amounts of Fe and Al sesquioxides. We compared the effect of wet pomace applied at amounts ranging from 0 to 210 Mgha−1, incorporated 60 days prior to sunflower sowing. In the wheat lateseason of thesecond year, average samples fromthe 0–0.60 m layerweretaken and testedforstructural stability,organic matter,totalnitrogen, available phosphorus, exchangeable potassium, pH and saturation extract electrical conductivity. The results indicate that the application of wet pomace induces ageneral improvement insoilfertility.Inparticular,theincorporation ofincreasing amounts ofwet pomace improvednutrient content. For instance, an application of 210 Mgha−1 of wet pomace increased soil organic matter by +84%, total N by +0.90 gkg−1, available P by +79.40 mgkg−1 and exchangeable K by+80 mgkg−1.We also observed an improvement in soil structure,which isof particular importance in hot, arid environments and insustainable agricultural systems.