Il compost da residui di Posidonia: un possibile sostituto della torba nella formulazione dei substrati

Posidonia oceanica (L.). Del. is the main marine seagrass endemic of the Mediterranean Sea. From September on, leaves and rhizomes detach off the marine plant and accumulate on beaches in huge amount. Offshore residues represent an environmental, economical, social and hygienic problem because of the great disturb to the bathers and citizens and high costs that the public administrations have to support for managing them. Nowadays, current Italian legislation (D. L. n. 75/2010) allows the use of posidonia residues as raw material for the production of compost even though at a rate of 20% by weight. In an experiment posidonia residues have been used to produce green compost. This was used as a substrate for the cultivation of tomatoes in soilless subirrigation system. Plants grown on compost showed a lower production (18%) compared to perlite: peat (control), but fruits had the same quality characteristics (as dry matter and soluble solids). On the other hand, the same compost represented a viable alternative to peat when used for the production of lettuce transplants. In particular, lettuce seedlings grown on compost showed higher fresh and dry weight of leaves and roots, length and volume of the root system, and leaf area, if compared with those grown on peat alone.