"Olive pressed solid residues as a medium for growing mushrooms and increasing soil fertility".

Organic fertilizer is the core of organic farming, which represents the most important way to provide crops and agricultural products that are safe and free of any chemical components and pesticides. From this point of view, the purpose of this study is to provide a source of organic fertilizers which was formerly an environmental problem. The northwestern region of Saudi Arabia is flourishing with olive production, leaving huge amounts of residues called olive press cake (OPC). These wastes are a major environmental pollution despite their good content of carbohydrates, protein, oil and cellulose alongside phenols and lignin. We tested the cultivation of Gliocladium roseum, Pythium oligandrum and Trichoderma harzianum and the mushroom Pleurotus ostreatus on OPC in order to reduce the high percentage of phenols that impede the germination of some plant seeds. Gliocladium roseum, Pythium oligandrum and Pleurotus ostreatus were able to reduce the percentage of phenols to more than 40% and thus support germination of seeds of Eruca sativa. This study gave than one benefit: firstly, reducing phenols that impede the germination of seeds. Secondly, Gliocladium roseum and Pythium oligandrum work against some plant diseases and also produce plant-like hormones that increase growth of plants.