Improvement of soil properties by application of olive oil waste

Abstract

Wet olive pomace is an 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 with 3 crops in succession: sunflower-wheat-wheat. The experiments were conducted at the Agricultural Faculty of Bari, 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 Mg ha−1, incorporated 60 days prior to sunflower sowing. In the wheat late season of the second year, average samples from the 0–0.60 m layer were taken and tested for structural stability, organic matter, total nitrogen, available phosphorus, exchangeable potassium, pH and saturation extract electrical conductivity. The results indicate that the application of wet pomace induces a general improvement in soil fertility. In particular, the incorporation of increasing amounts of wet pomace improved nutrient content. For instance, an application of 210 Mg ha−1 of wet pomace increased soil organic matter by +84%, total N by +0.90 g kg−1, available P by +79.40 mg kg−1 and exchangeable K by +80 mg kg−1. We also observed an improvement in soil structure, which is of particular importance in hot, arid environments and in sustainable agricultural systems.