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The increasing demand for soilless media for horticultural crop production and the rising environmental concerns about the use of non-renewable resources such as peat as substrate has led to the search for alternative materials as constituents of growing media, such as waste organic by-products. Also, biogas production through the anaerobic digestion of organic wastes generates a potential fertilizer, the digested substrate (digestate). The aim of this work was to study the feasibility of using the composted solid fraction of a digestate obtained after the codigestion of cattle manure and maize-oat silage as a component in the formulation of growing media for the commercial seedling production of three species: tomato (Lycopersicon esculentum Mill.), muskmelon (Cucumis melo L.), and pepper (Capsicum annuum L.). Four substrates were compared: pure peat (control) and three mixtures containing 25%, 50%, and 75% by volume of compost with the corresponding amount of peat. Physical, physicochemical, and chemical analyses of the different growing media were carried out and the effects of the different mixtures of peat/compost on seed germination and on the nutritional status of the seedlings were also studied. In general, compost addition neither influenced negatively the physical and physicochemical properties nor produced any reduction in the germination rate in the species studied, but it did enhance the seedlings' nutritional status.

253-264. The aim of this study was to evaluate the economic feasibility of using compost made from anaerobically digested cattle slurries in a commercial nursery. Using a comparative cost analysis, commercial peat substrate growing media has been partially substituted with increasing proportions of compost (25, 50 and 75% v/v of compost). This experiment was intended to establish the conditions under which the use of these composts is feasible and competitive relative to commercial peat, at both agronomic and economic levels. Neither the quality of germination nor the vegetative development of the seedlings selected for the experiment (tomato, melon and pepper) were compromised, which was a necessary condition of peat substitution. In addition, the economic effects of using alternative compost media instead of peat alone have been quantified. The results showed that the most suitable scenario from an agronomic standpoint is to substitute 25% of the peat with compost because higher proportions of compost in the growing media are more limiting, especially for the tomato crop. At an economic level, reductions of up to 43% of the substrate cost and a 4.6% improvement in the commercial contribution margin for a company in this sector resulted from 50% peat substitution.