Annual spreading of olive mill wastewater over consecutive years: Effects on cultivated soils' physical properties

Several studies cautioned against potential negative effects of controlled olive mill wastewater (OMW) application on soil physical properties that could be associated with the possible adverse effects of K on soil structure stability. The objective of the study was to examine the effects of annual application of OMW over several years on selected physical properties of the upper soil layer (0-10cm) and their link to exchangeable K levels. Two experimental field platforms were studied: field crops grown in a tilled clay soil (3years of OMW application) and an olive orchard grown in a sandy-loam soil (5years of OMW application). In the clay soil, OMW application did not affect organic carbon (OC) and only slightly increased exchangeable potassium percentage (EPP) from 3.3 in the control to similar to 4.5 in the OMW-treated plots. In the sandy-loam soil, application of different rates of OMW resulted in an increase in both OC and EPP (>20) compared with the control (8). For both soils, addition of OMW improved aggregate stability; yet for the clay soil, the increase was not associated with changes in EPP or OC. In the sandy-loam soil, aggregate stability was positively correlated with OC and EPP. Soil hydraulic conductivity, tested for the sandy-loam soil only, was not affected by OMW application. Overall, our study shows that consecutive 3 to 5years of controlled OMW application in the range of 50-150m(3) OMW ha(-1) y(-1) does not result in the deterioration of soil physical and hydraulic properties.