Effects of irrigation volumes and organic fertilizers on eggplant grown in Mediterranean environment

A three-year field experiment was carried out in Mediterranean conditions to study the effects of different irrigations and organic fertilizers on yield, quality and nitrogen utilization of eggplant crop and on soil properties. In a split-plot design, two irrigation treatments (re-establishing 100% and 50% of the calculated maximum evapotranspiration) and four fertilizer treatments (mineral fertilizer, commercial stable manure, anaerobic digestate and municipal solid waste compost) were compared. The highest water volume increased significantly the total and marketable yield, the number of marketable fruits, the dry matter of fruits and the nitrogen-use efficiency with respect to the treatment with the lowest irrigation. Nevertheless, the same treatment decreased significantly the fruit dry matter percentage and total soluble solid content. The lowest water volume led to an improvement of fruit quality. Anaerobic digestate increased significantly the total and marketable yield and dry matter compared with compost. Harvest index, nitrogen harvest index, pH, acidity and total soluble solids did not show significant differences among all fertilizer treatments. N translocation ability of plants and fruit quality were not influenced by the type of fertilizer. At the end of experiment, anaerobic digestate and compost reached the highest levels of soil total organic carbon and humic and fulvic acids content. Besides, anaerobic digestate increased the total extractable carbon, phosphorus and nitrogen content compared to all other treatments. Soil copper, nickel and lead content in all treatments enhanced compared to that at the beginning of experiment, but this accumulation did not represent a possible environmental risk. The content of heavy metals in the soil, after 3 years of application, did not exceed the limits imposed by the Italian law. This study showed that the organic wastes, after being adequately processed, could be applied successfully in agriculture especially in arid environments, characterized by quick mineralization and very low organic matter content.