Chemical and Microbiological Characterization of Olive Mill Wates Based Substrata Produced by the (O.Mi.By.P.) technology (olive mill by-products processor) and their Grounds Amendment

An innovative technology for pomace and olive mill waste water recycling for agronomic goals was highlighted by the Oliveculture Section of ISAFoM-CNR of Perugia, Italy, in the context of the European project Life Environment-TIRSAV (www.lifetirsav.com). Olive wastes without stones are mixed with appropriate hygroscopic organic wastes, producing a non-percolating and non bad-smelling substratum, where aerobic microbial metabolisms occur. Substrata are packaged in net sacks, stored and amended on site when requested by cultural conditions. In this work two experimental storage systems were compared to study their physical, chemical and microbiological modifications: 1) outdoor stratification of net sacks substrata, protected against precipitation and 2) net sacks substrata piled inside a warmed greenhouse. In addition, different substrata were tested as amendment/fertilizer at a rate of 6 tonnes per year of dry matter per hectare, in an intensive olive grove in comparison to a standard mineral fertilizing system, and vegetative and productive parameters were recorded over four years. Important chemical changes occurred during the storage period: mass dehydration, increased pH and specific electric conductivity, and polyphenols-degradation. Moreover, substrata presented an interesting content of plant nutrients, in particular Potassium, Nitrogen, Calcium and microelements (Magnesium, Iron, Manganese, Zinc and Copper). Microorganisms in the raw Olive Mill Wastes had CFU values of 9.4x107-1.1x108 per gram of fresh weight, and were mainly yeasts. At milling, yeasts were the prevailing microorganisms in the substrata, whereas during storage, both in the cold and warm conditions, bacteria seemed to become the most representative microorganisms (1.8x108 CFU) probably linked to the increase in pH, detected in the same substrata. Few moulds were present in the different storage conditions. Microorganisms able to degrade aromatic compounds were also present at different times in the stored substrata. Vegetative and productive parameters, detected in the field experiment, showed no statistically significant differences between the standard mineral fertilizing system and Olive Mill Wastes Based Substrata amendments.