147 Proc. Int. Symp. on Composting of Organic Matter Eds. Balis et al. A cta Hort. 549, ISHS 2001 EVALUATION OF DIFFERENT COMPOSTS FROM HORTICULTURAL CROP RESIDUES AND THEIR USES IN GREENHOUSE SOILLESS CROPPING M. Urrestarazu, M.C. Salas and M.I. Padilla Dept. Producción Vegetal Univ. of Almería E O4120 Almería. Spain e-mail mgavilan@ual.es J. Moreno and M.A. Elorrieta Dept. Biología Aplicada, Univ. of Almería. Spain G.A. Carrasco Dept. Horticultura Facultad de Cs Agrarias, Univesidad de Talca, Chile Keywords : compost, soilless crop, environment Abstract The aim of this work was to evaluate the possibility of using different composts from horticultural residues under forced ventilation conditions and different levels of inoculation of microorganisms. All compost treatments started with a similar volumetric ratio: 2 parts of pepper : 1 cucumber : 1 runner beans : 1 wooden material (sawdust and industrial shavings). Several inoculation methods were evaluated with controlled humidity and using forced ventilation and turn over. The evaluation trials were: germination assays, growth test and yield using watercress and lettuce, melon, and tomato cherry respectively. We conclude that these composts can be utilised not only as compost amendment but as horticultural and environmentally friendly substrates. Also they are able to substitute for other traditional substrates such as peat. 1. Introduction Almería Province located in the Southeast of Spain, generates approximately 422,900 mtyear -1 of solid plant residues from greenhouses (Escobar, 1998). This situation results in infection foci for pests, microorganisms, rats and insects; and other environmental changes such as pollution of soil by toxic elements, effluent run-off, generation of bad smell, etc. In relation to this, Conway (1996) indicates that an important factor in sustainable agriculture is the need to eliminate the harvest residues in these crop areas having protected systems such as greenhouses. Controlled composting seems to be an important way to eliminate residues and reusing those materials as organic amendments. Also, there is a need for new substrates as alternative soilless media. (Pudelski, 1987; Abad et al., 1993a; Soliva, 1998). These should have similar characteristics to existing environmentally friendly substrates such as coconut coir waste (Noguera et al., 1999). Composting is a process involving biological aerobic breakdown of organic residues under controlled conditions (Gouleke, 1972; Hoitink & Fahy, 1986). The nature of initial organic matter is an important factor in the development of composting processes due to its composition and physical-chemical characteristics, which depend on the residues source (Gouleke, 1992). It is known that different processes take place during general composting (Crawford, 1985; Biddlestone & Gray, 1991; Gouleke, 1992) and each phase (Fogarty & Touvinen, 1991. It is very important to consider that when composting is unsuitable or immature, phytotoxic substances ca arise (Chanyasak et al., 1983; Hoitink & Fahy, 1986). In order to obtain a correct and rapid maturity of compost, and therefore removal of phytotoxic substances, it is beneficial to provide forced ventilation (Fogarty & Tuovine, 1991; Nakasaki et al., 1992) and a suitable level of microorganism-inoculation, although this last factor was variable under certain conditions (Crawford et al., 1993). The aim of this work was to evaluate the possibility of using different composts from horticultural residues under forced ventilation conditions with different levels of