The compost of posidonia residues: A short review on a new component for soilless growing media

Posidonia oceanica (L.) Delile 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 amounts, forming banks on the foreshore and backshore of beaches. Offshore residues represent an environmental, economical, social and hygienic problem, because of the great disturbance to the touristic activities, citizens life in urban areas and high costs that the public administrations have to support for managing them (beach cleaning, transport and disposal of such a biomass). Nowadays, current Italian legislation (n. 75/2010) allows the use of posidonia residues as raw material for the production of compost although at a maximum rate of 20% by fresh weight of the composting mixture. High presence of sand mixed to residues after removing from beaches and high salinity levels represent at the moment the main obstacles to the large use of this biomass as raw material for composting. Studies have been conducted, in the framework of the Life09 "Posidonia Residues Integrated Management for Eco-sustainability" (P.R.I.M.E.) project, with the aim to increase the application of posidonia residues for compost production, demonstrating the possibility to effectively separate the sand from the organic material and reduce the salinity levels. Several tests have been carried out with the objective to assess the posidonia-based compost quality. Posidonia-based compost proved to be a good peat substitute for lettuce transplant production and a good growing media component for greenhouse tomato and lettuce in soilless conditions. According to our studies, beached posidonia wastes could represent a low cost and renewable raw material for composting. Posidonia-based compost presents interesting properties and can be used as horticultural growing media component.