EVALUATION OF TEMPORALVARIATIONS IN MOISTURE AND CALORIFIC VALUE OF VINE AND OLIVE PRUNING

In Italy arboreal crops, in particular vine and olive, cover a surface area of around 19.6×109 m2 from which about 4.6×109 kg of pruning are cut. These by-products are currently ploughed into the soil or else harvested and burned in open fields. On the other hand such materials would be more useful as an energy source. If these materials are to be used as fuel, it is important to know their calorific value. The calorific value is significantly influenced by the moisture content of wood. This work has evaluated the changes in moisture content and calorific value with time for different harvesting and storage systems of vine and olive pruning. The observed decrease in the moisture content of the vine and olive pruning depended on the storage system utilized, in particular on the product compression ratio and air circulation. Some differences were observed between the results obtained for vine and olive pruning. The time required for these materials to obtain their best energetic performance was identified at 32 weeks from their harvesting. Harvesting with balers and forwarding costs are about 6.21×10-2 €/kg for vine pruning and 4.64×10-2 €/kg for olive pruning. They are very similar to the price currently offered for energy biomass in Italy (5.00×10-2 €/kg). While the cost actually paid to plough pruning into the soil amounts to about 2.50×10-2 €/kg. Therefore the energy chain encourages a cost-and-benefit analysis.