ENERGETIC VALORIZATION OF THE BIOMASS FROM OLIVE REJUVENATION PRUNING OF TRADITIONAL OLIVE ORCHARDS

Traditional olive groves are generally characterized by low planting density, considerable age of the trees, large size of the canopies and alternate fruit productions so that a rejuvenation pruning is highly required. In this context, pruning residues are usually burned by the farmers. The present paper is finalized to assess the production of biomass from rejuvenation pruning of a traditional olive orchard in Southern Italy and to characterize it in order to evaluate its potential energetic value according to dimensional classes. A four-year study was carried out to evaluate the effect of rejuvenation pruning on the olive trees. In particular, an intense pruning by immediately selecting the final primary branches of the canopy was applied in ‘Carolea’ cultivar in 2019 and shreddable and non-shreddable removed materials were separately collected and weighted per tree in each year of experimentation. Pruning material was also analyzed according to dimensional classes in order to evaluate the possibility for energetic use. Results showed that the amount of removed material was very high in the first year of pruning with a ratio around 1.0 for shreddable and nonshreddable fractions. Pruning intensity strongly decreased during the following years with a prevalence of shreddable material and a very low pruning time requirement for tree. The energy characteristics of olive pruning residues recorded significant differences only for the sample with diameter < 20 mm (shreddable foliage) confirming the suitability of the bigger fraction (> 20 mm) to be used for the production of olive pruning pellets for domestic use (boilers even with low thermal powers) respecting the limits of class B of EN ISO 17225-2. In conclusion, while shreddable pruning material was the prevalent fraction and it can be useful to improve the soil organic matter content if maintained in the olive orchard, non-shreddable fraction can offer an interesting source for energy production. In particular, it can represent a secondary source of income for the farm to recover the cost incurred for the rejuvenation pruning of the traditional olive orchard or to design interesting alternative agricultural energetic supply chains.