Plant residue based compost can replace peat in growing media for organically grown olive tree saplings in Mediterranean climates

Increased environmental concerns over the use of peat for seedling and sapling production has stimulated a quest to find peat alternatives to improve the sustainability of agroecological production systems in Mediterranean climates. This study aimed to develop the use of locally sourced recycled plant residues as effective alternatives to peat in horticultural growing media. The trial was conducted using a randomised plot design with four treatments and four replications. Growing media formulations based on olive tree prunings processed in different ways were tested in a trial for the production of olive saplings in pots under organic management. The trial included four growing media treatments: 1) formulation based on compost made from 70% olive prunings (COMP); 2) a mixture of chipped (50%) and extruded fibre (50%) of olive prunings (FIBRE), 3) commercial medium based on sand and vermiculite (SAND; control); and 4) commercial medium based on peat and coir (PEAT, control). According to the results, after 24 months, the vegetative growth (above-ground parameters) of olive sapling grown in COMP was similar to that for saplings grown in PEAT. At 24 months, saplings grown in COMP had the highest number of roots and the largest root architecture. Saplings grown in FIBRE were smaller than those grown in COMP or PEAT, but they had longer primary roots. It was concluded that the plant-based, mature compost, enriched with bacteria and Trichoderma, provided an effective alternative to peat for sustainable cultivation of olive saplings in Mediterranean climate areas.