Peat replacement is an increasing demand in containerized and transplant production, due to the environmental constraints associated to peat use. However, despite the wide information concerning the use of alternative materials as substrates, it is very complex to establish the best materials and mixtures. This work evaluates the use of mixture design and surface response methodology in a peat substitution experiment using two alternative materials (green compost and palm fibre trunk waste) for transplant production of tomato (Lycopersicon esculentum Mill.); melon, (Cucumis melo L.); and lettuce (Lactuca sativa L.) in organic farming conditions. In general, the substrates showed suitable properties for their use in seedling production, showing the best plant response the mixture of 20% green compost, 39% palm fibre and 31% peat. The mixture design and applied response surface methodology has shown to be an useful approach to optimize substrate formulations in peat substitution experiments to standardize plant responses.

Compost based substrates for producing organic tomato seedlings (Lycopersicum esculentum L. cv. Rio Grande) were evaluated in a peat substitution experiment. Two composts made from olive pomace waste (OWC) and green waste (GWC) were produced and characterized, in comparison with a sphagnum peat moss, for the main physicochemical parameters and for their germination index. Both composts were used as growing media components at four rates (20%, 45%, 70%, 90% on a volume basis) and their performances were compared to peat based control growing media. During plant growth, nitrogen was added as blood meal. Plants were collected 36 days after sowing, plant performance parameters (stem length, leaves, stem and total fresh and dry biomass, leaves number and chlorophyll content values), and NPK shoot contents were measured. Treatments GWC 20%, 45% and OWC 20% showed the best performances, while 70% for green waste compost and 45% for olive pomace compost could be considered as upper limits for producing satisfactory organic tomato seedlings.