COMPOSTING OF OLIVE MARC

Large quantities of olive marc are obtained as a by-product of olive oil extractions. We thought that it could be used as a substrate in horticulture, after an adequate composting process, which was controlled in cubical rotting boxes with 0.5 m sides. Periodically, temperature, pH, electrical conductivity, total-nitrogen, ammonium-nitrogen, nitrate-nitrogen, organic matter content and the degree of decomposition were measured. No additives were applied to olive marc, only water was added three times within the first two months, while aeration was induced by turning the material in order to avoid anaerobic conditions. After two months, when compost had cooled to ambient temperature, pH was near 8, C/N ratio was near 15, the degree of decomposition had increased and organic matter content had decreased as well as electrical conductivity. Emergence of cucumber and lettuce seedlings was still low in two month old compost, but germination was improved by leaching with water or mixing the compost with perlite or sand. A gas chromatographic analysis gave 400 to 600 ppm of acetic and considerable amounts of other organic and fatty acids. After 120 days of composting, none of them was detectable and emergence increased in pure compost.