Olive Mill By-products Application: Organic Olive Orchard Yield Performance and Soil Fertility

Seasonal accumulation and incorrect disposal of olive mill by-products may be detrimental to the environment. Conversely, their proper recycling as soil amendments may be a sustainable solution. Therefore, the objectives of this three-year field trial were: (i) Investigating the effects of Olive Mill Wastewater (OMW) and Pomace Compost (PC) on plant nutritional status and yield in an organic olive grove; (ii) The impact on main soil properties, and (iii) Verifying if these experimental fertilizers can replace the widespread fertilization practices. The OMW and PC treatments were compared to a commercial Organic-mineral Fertilizer (OF) and green manure of horse bean (MV). Plant nutritional status, soil properties and agronomical performance of treatments were assessed. The OMW and OF determined yield that was on average significantly higher than MV and PC by 191 and 55%, respectively. The best leaves P contents in PC indicated a more effective release of this nutrient as compared to the other treatments, which can be matched with more favorable soil conditions. The comparable yield and leaves composition for OMW and OF suggested the possibility to replace the OF with the OMW. The effects on olive oil production and soil fertility highlighted that OMW (and PC as a second choice) could be applied to sustain olive tree production, substituting traditional fertilizers.