Testing peat-free growing media based on olive wood residues for olive saplings

For environmental conservation, peat-based growing media are being phased-out in many countries. Peat-free alternatives need to be developed, preferably from local biomass ingredients. This paper describes the performance of peat-free substrates containing olive branch pruning materials in comparison with commercial growing media controls for olive saplings grown during April-October 2020 at the Olive Research Institute (ORI) in Turkey. The trial was conducted using a randomized plot design with 4 replications and 4 treatments: 1) (COMP) compost made of locally available plant materials with 70% olive prunings (100%, v v^-1; 2) (FIBER) mixture of chipped and extruded olive prunings (50% chipped + 50% extruded, v v^-1); 3) (SAND) a commercial mixture(sand 90% + vermiculite 10%, v v^-1) (control); and 4) (PEAT+) a commercial mixture (peat 40% + coco coir 40% + perlite20%, v v^-1) (control). The vegetative growth parameters and weed status (density and coverage) were recorded and root fungal diseases commonly found in Turkey were analyzed. After the first six months of growth, there were statistically significant differences between the treatments (p≤0.05); COMP and PEAT+ were comparable and produced the largest plants with 100% survival rate. 98% of plants survived in SAND, and 81% in FIBER.FIBER, which was the only treatment with no weed growth, had about 30% reduced growth as compared to SAND, which had 90 and 78% growth compared with PEAT+ and COMP. Still, it was remarkable that it was possible to grow olive saplings in treated olive prunings. It is very promising that a peat-free growing media like COMP performed as well as the commercial growing media with 40% peat. During the extrusion of olive material, the temperature rose to ca. 120°C and during composting the COMP reached 65-70°C; temperatures at which the materials are expected to be effectively sanatised from any fungal diseases.