The production of an organic fertilizer was carried out, from waste generated in the winemaking process of white (Riesling Italian-RI) and red (Cabernet Sauvignon-CS) grapes obtained from the vineyard of Pietroasa (Romania). The potential of the biotransformation process of by-product marc in an open pile in the autumn-winter season was controlled and the thermophilic phase reached average values of 60 ºC at a neutral pH which gives it suitable characteristics to be used as a soil fertiliser. The values of the germination index (GI) of Lepidium sativum L. seeds, using water dilutions from the RI and CS compost marc, demonstrated that there was no degree of phytotoxicity (average GI 144.2% and 139.8%, respectively). The compost marc microflora was represented by bacterial and fungal isolates belonging to genera Rhizopus (10%), Aspergillus (80%), and Penicillium (17%), compared to by-product marc that only present fermentation yeasts. The structure of the microorganism populations in the compost marc dried by lyophilisation showed an almost double number of CFUg-1 compared to the oven-dried compost. The presence of potential antagonistic microorganisms and the high number of CFUg-1, demonstrated that this compost can have a suppressive effect on soil pathogens in addition to its quality as a fertilizer.
