NEW POPLAR GENOTYPES FOR SHORT-ROTATION BIOMASS PLANTATIONS IN THE MEDITERRANEAN ENVIRONMENT: PRODUCTIVITY AND QUALITY OF BIOMASS FOR BIOREFINERY

Short-rotation woody crops have been recently included in the latest guidelines on the EU's "greening" of the new Common Agricultural Policy (CAP). For the implementation of this measure it is necessary to identify species adapted to different climatic conditions to be evaluated for the production and quality of their biomass. For this purpose, an experimental poplar plantation (1.5 ha) was established in 2009 near Viterbo with a density of 6060 cuttings ha-1 and three-year rotation. Eight new poplar genotypes were compared with Monviso, AF2 and AF8, already in use in commercial plantations. The drip irrigation, conducted in the summer period with irrigation volumes of approximately 100 mm-1 has covered the 30-60% of the optimal water demand of the culture. At the end of the second three-year rotation dry biomass production was evaluated into its component (branch and stem) and qualitative biochemical analyses were conducted to highlight the potential for biorefinery. The dry biomass production was not significantly different between the clones under investigation, with an average production of 13.7 Mg ha-1 in three years. The best clones were AF24 and AF17, with a higher productivity on the average of about 20%. AF24 has allocated in the stem the largest amount of biomass (14.5 Mg ha-1). The biomass of the branches was on average equal to 16% of that total, with the bark representing about 40% of this segment. Also interesting is the variability observed for the survival of the sprouts at the end of the second rotation, with average values at clonal level from 1.9 (AF19) to 5.3 (AF16) shoots per stump. Differences in the allocation of the biomass on the different diameter classes (CD) affected the percentage of bark (Bark%) on the total biomass and, therefore, its qualitative characteristics. In the stem Bark% was variable, from 50% for the 1 cm CD (DBH) up to 20% for the CD over 6 cm. There were not significant differences among clones in Bark%. The qualitative analysis of biomass highlighted significant differences among genotypes in the composition of ashes, total extractives, lignin, and non-structural carbohydrates. The obtained results will be discussed to improve the selection of poplar genotypes for different traits in the Mediterranean environment.