Harvesting orchard pruning residues in southern Piedmont: a first evaluation of biomass production and harvest loss

In recent years, interest in farming residues has grown and orchard pruning residues are no exception. Several factors define pruned branch mass and dimensional characteristics: fruit variety, vigor, training system used, and pruning intensity and periodicity. While many studies have been performed to determine residue biomass availability, dating and surveying are not always accurate. Detailed qualitative and quantitative knowledge is needed to evaluate the economic sustainability of exploiting orchard pruning residues as an energy source. To assess the real chain potential of renewable energy production from orchard pruning residues in the area of Cuneo, in the Region of Piedmont, northwestern Italy, a study was conducted on the species Actinidia (kiwi tree) pruned according to the Peyracchia system, and Malus (apple tree) pruned according to two different systems, i.e. traditional and taille longue. For each species, pruning residue amounts were quantified and their basal diameter measured. Surveys were performed on some half trees, spaced as crop, for three randomised replications. Pruning residues were determined by dynamometer (accuracy 0.02N); individual cut-off branch diameters were measured at their base with mechanical calipers. Pruning residues were blown by rotating rake and harvested by a modified fixed chamber round baler. Harvest losses were determined by the methodology used for the initial residue quantification. Results showed the average biomass availability was 2.51 Mg DM ha^–1 (SD 0.83) for kiwi tree, 3.04 Mg DM ha^–1 (SD 1.17) for traditionally-pruned apple trees, and 0.46 Mg DM ha^–1 (SD 0.36) for apple trees pruned with the taille longue system. Harvest losses (total pruned dry mass) averaged approximately 19% in kiwi trees and 16% in apple trees (95% to 10% for variety)