Olive-mill and grape-mill waste as a substitute growing media component for unexploded vegetables production

Olive tree and grapevine cultivations are the main crops in the Mediterranean area, resulting to high yields but also a great amount of wastes after processing, with environmental and human health concerns, after their disposal. The present study was conducted in order to evaluate the potential use of olive-mill wastes (OMW) and grape-mill wastes (GMW) in different ratios (0-5-10-20-40% v/v) with peat, as a peat substitute material, for the production of Portulaca oleracea (purslane) and Sonchus oleraceus (sowthistle) plants. Both GMW and OMW addition in the substrate mixture affected purslane's and sowthistle growth and disturb plant's physiological metabolism at ≥20% and ≥10% of the waste, respectively. Sowthistle plants that grew with GMW up to 10% on the substrate, had increased growth indicators (or remained unaffected) compared to the control. Leaf stomatal conductance was decreased proportionally with the increase of the ratios the tested materials into the growing mixtures. The antioxidant status of both plants was significantly affected by the addition of the waste materials into the growing media. Plants in cases appeared to be under stress conditions, as this was revealed by the increment in stress indicators as the lipid peroxidation and the internal concentration of hydrogen peroxide, and as a consequence, antioxidative (catalase, superoxide dismutase, peroxidase) enzyme metabolism was found increased. It can be concluded, that both GMW and OMW have the potential to be used in the growing media at low ratios of 10% and 5%, respectively, providing healthy plants, with increased antioxidant and mineral value.