Agronomic exploitation of olive oil mill wastewater: effect on growth and yield of field crops and impact on soil fertility

In Mediterranean countries, olive oil mills generate a liquid waste that could represent a potential source of pollution or an agronomic opportunity if recycled as fertiliser within the agrosystems. Hence, the effects of applying increasing amount of this effluent (0, 8, 16, 32 l m-2) on growth and productive response of a series of field crops (forage sorghum, faba bean, durum wheat, berseem, malting barley, sulla meadow) as well as on the main soil properties were studied. The research was conducted in southern Italy using lysimeters as plots. The results highlighted that with the exception of faba bean, which experienced phytotoxicity with deleterious effects at higher rates of the effluent, the other tested crops were not penalised and responded positively in terms of plant survival, growth and yield as the waste supply increased within certain limits. Therefore, each crop reached the best productive performance with different level of residue. However, the favourable rainfall regime during the growing season of the crops played a key role. At soil level, changes emerged between the start and the end of the experiment for the analysed features, except those for pH and EC. Overall, the organic pool of the soil was relatively preserved, whereas an enhancement occurred for C.E.C. and for macronutrients, mainly P and K. The micronutrient levels also varied differently. However, the final variations of the soil characteristics were not always univocally sustained by the different waste rates. In conclusion, there are real possibilities of agronomic reutilisation of the waste in cropping systems typical of southern Italy, but others research into farming studies are needed to acquire a better evaluation of the environmental impact.