Product contamination and harvesting losses from mechanized recovery of olive tree pruning residues for energy use

The authors tested six commercial pruning harvesters to determine harvesting losses and product contamination when recovering pruning residues from an overgrown olive orchard, typical of Southern Italy. All harvesters used a mechanical pick-up to collect the residues and a shredder to reduce them into chips. Three different pick-up settings were tested and namely: 1 cm above ground level, manufacturer's specification and 3 cm above ground level. Ash content in the shredded material was taken as a measure of contamination. The ash content of uncontaminated branch material collected directly from the trees was 3.5%. Ash content in shredded residues varied between 4.5% and over 5.5%, for the shortest and the longest distance between the pick-up and the soil surface, respectively. In contrast, harvesting losses were weakly (but significantly) related to pick-up setting, and mainly depended on machine type.

► Pruning of olive tree groves can offer up to 14 green tonnes of biomass per hectare.
► Pruning recovery tests were conducted with 6 different machines, at 3 different settings.
► Harvesting losses were strongly related to machine type, possibly due to different work width.
► Residue was contaminated with soil during collection.
► Contamination was strongly related to machine setting (pick-up height).