Response of Soil Properties and Microbial Communities to the Application of Olive Mill Wastewaters

A laboratory trial was carried out to evaluate the short-term influence of different concentrations of olive mill wastewaters (OMW) on soil physico-chemical properties and microbial community. After 30 days’ incubation, no significant changes occurred in soil pH values and humified organic carbon; soil organic carbon and total water-soluble phenols (WSP) significantly increased. Addition of OMW to the soil caused modification in microbial counts and microbial community structure. Bacteria decreased significantly up to 86% for 100% OMW treatment. No significant differences were found for fungal community in the soil treated up to 50% OMW while a decrease in 50% was found when 100% OMW was applied. The fungal: bacteria ratio increased significantly. The actinomycetes CFU (colony forming units) decreased gradually up to a maximum of 38% when OMW dose increased. Our results evidenced that the storage of OMW in open-air lagoons for a 4-month period before its soil application and the appropriate dilution with irrigation water without any further treatment can be an inexpensive technology to be adopted by small-sized olive mills.