Posidonia-based compost as a growing medium for the soilless cultivation of tomato

High quality compost could be used as an environmentally friendly and renewable component for soilless growing media. Beached residues of posidonia (Posidonia oceanica (L.) Delile), a marine phanerogam endemic to the Mediterranean Sea, can be used as raw material for compost production. The aim of this study was to evaluate a posidonia-based compost as a soilless growing medium component for the cultivation of tomato. Beached residues of posidonia (20% in weight) and green wastes were composted. The compost, alone (Compost 100%) or mixed with perlite at the rate of 50% in volume (Per-Comp 50:50), was used as growing medium and compared with traditional perlite (Perlite 100%). Tomato plants (cv. ‘Ikram’ ungrafted, ‘Ikram’ grafted onto ‘Beaufort’ and ‘Ikram’ grafted onto ‘Arnold’) were grown in the three growing media. A complete nutrient solution (EC = 1.7 dS/m; pH = 5.0) was used for fertigation. A system composed by EC5 soil moisture sensors, a data logger and a rely controller, and tensiometers to check water potential was used to manage fertigation, with the aim to maintain easily available water. Forty five days after transplanting, the plants grown in 100% compost as well as in the compost/perlite mix resulted in higher growth. Leaf area, total fresh and dry weight increased with increasing amounts of compost in the substrate. The tomato yield in Compost 100% and Per-Comp 50:50 treatments resulted higher than Perlite 100%, in terms of weight and number of fruits (15 and 7%, respectively). Grafted plants, regardless of the rootstock, showed a higher total yield if compared with ungrafted plants (11%, on average). The quality profile of fruits was only slightly influenced by growing media, while was not by the grafting combination. The results show that the compost-based posidonia could be successfully used as soilless substrate component for growing tomato.