Biomass production and Energy balance of a 12-year-old short-rotation coppice poplar stand under different cutting cycles.

Given today's political targets, energy production from agricultural areas is likely to increase and therefore needs to be more sustainable. The aim of this study was thus to carry out a long-term field trial based on the poplar short-rotation coppice (SRC), in order to compare dry matter, energy-use efficiency and the net energy yield obtainable from this crop in relation to different harvest frequencies (1-, 2- and 3-year cutting cycles). The results showed that poplar SRC performed very well under temperate climates as it can survive up to 12 years, providing a considerable annual biomass yield (9.9, 13.8, 16.4 t ha−1 yr−1 for annual T1, biannual T2 and triennial T3 cutting cycles, respectively). The system tested in southern Europe showed a positive energy balance characterized by a high energy efficiency. We found that the choice of harvest interval had huge consequences in terms of energy yields. In fact, the energy efficiency improved from T1 to T2 and T3, while the net energy yield increased from 172 to 299 GJ ha−1 yr−1. This study suggests that, with 3-year harvest cycles, poplar SRC can contribute to agronomic and environmental sustainability not only in terms of its high yield and energy efficiency but also in terms of its positive influence on limiting soil tillage and on the environment, given its low pesticide and nutrient requirements