Waste materials-based substrates for ornamental plant production: technical and environmental aspects

In the plant nursery sector, efforts have been made for some time to partially or totally replace peat-based substrates with growing media characterized by a lower environmental impact. In this perspective it was decided to evaluate a composted material obtained from dredged sediments and green waste, to be used as component for substrates in ornamental plant production, while evaluating the environmental implications of this operation. Fresh green waste consisting of corn cob, wood chips, grass and leaves were mixed in different rates (3:1, 1:1, 1:3 v/v) with dried dredged sediments taken from a small stream located in an urban area (?ejkovice, Czech Republic). These different mixtures were co-composted for six months, and the compost heaps were managed following standard compost protocols. To evaluate the progress of the co-composting process, the various mixtures were subjected to physical, chemical and biological analysis, during the entire period of co-composting. Eventually these mixes were taken to a plant nursery farm in Pistoia (Tuscany, Central Italy), and mixed in different ratios with classical nursery growing media (peat and pumice). Then, one-year-old vegetatively propagated plants of two typical evergreen shrubs (Photinia × fraseri, Viburnum tinus) were placed in 10-L (24 Ø cm) pots with differentiated substrates, added with 4.5 g L-1 of Basacote®. The growth of the plants tested is monitored (dry mass storage); at the same time, it was decided to use an LCA (life cycle assessment) analysis, to quantify the CO2 emissions (kg CO2 equivalent) deriving from the different phases (inputs, energy, transport, structures, etc.) of the production process, assessing the effect of these growing mixes on the environmental sustainability of plant nursery production.