Cristiano Tozzini

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

Given todays 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.

Miscanthus × giganteus nutrient concentrations and uptakes in autumn and winter harvests as influenced by soil texture, irrigation and nitrogen fertilization in the Mediterranean

Fertilization has a great impact on GHG emissions and crop nutrient requirements play an important role on the sustainability of cropping systems. In the case of bioenergy production, low concentration of nutrients in the biomass is also required for specific conversion processes (e.g. combustion). In this work, we investigated the influence of soil texture, irrigation and nitrogen fertilization rate on nitrogen, phosphorus and potassium concentrations and uptakes in Miscanthus × giganteus when harvested at two different times: early (autumn) and late (winter). Our results confirmed winter harvest to significantly reduce nutrient removals by as much as 80% compared to autumn. On the other hand, a few attempts have been made to investigate the role of soil texture and irrigation on nutrients in miscanthus biomass, particularly in the Mediterranean. We observed an effect of soil mainly on nutrient concentrations. Similarly, irrigation led to higher nutrient concentrations, while its effect on nutrient uptakes was less straightforward. Overall, the observed differences in miscanthus nutrient uptakes as determined by the crop management (i.e. irrigation and nitrogen fertilization) were highlighted for autumn harvest only, while uptakes in all treatments were lowered to similar values when winter harvest was performed. This study stressed the importance of the time of harvest on nutrient removals regardless of the other management options. Further investigation on the environmental and economic issues should be addressed to support decisions on higher yields‐higher nutrient requirements (early harvest) vs. lower yields‐lower nutrient requirements (late harvest).

Biomass production and carbon balance of a short rotation forestry of Populus deltoides (clone Lux) under two different cutting cycles

The emissions of green house gases contribute to global warming. Consequently, renewable energies such as solar, wind power, hydropower and bio energy appear as alternatives for reducing these emissions. One promising source of renewable energy is forest biomass, for it is considered to have neutral CO2 balance. The problem is to quantify the amount of CO2 that is emitted for a certain amount of energy generated, compared to the CO2 emitted to generate the same amount of energy from a non-renewable source. In this paper we calculate biomass production and carbon dioxide balance of an eight-year-old Populus deltoides short rotation forestry (SRF) under two cutting cycles (harvesting every two years, biennial and every three years, triennial). We also compare the amount of energy generated per kg of CO2 emitted in the use of fossil fuels versus the amount of energy generated per kilogram of CO2 emitted. On the one hand, total biomass yield was 12.6 ± 0.9 Mg ha-1 year-1 and 15.1 ± 1.5 Mg ha-1 year-1 for biennial and triennial cutting cycles respectively. On the other hand, total emissions of CO2 for growing a poplar SRF with a cycle of eight year and biennial cutting sequence reached a value of 738.8 kg ha-1 year-1; however, triennial short total emissions are equivalent to 695.5 kg ha-1 year-1. We concluded that the use of biomass makes a positive contribution to the reduction of greenhouse gases, in particular CO2, reducing emissions almost five times compared with fossil fuels.

Energy balance in a bioenergy plantation of Populus deltoides clone Lux in a site with Mediterranean environment.

Ante el desafio energetico al cual se enfrenta el mundo en general, y Chile no es una excepcion, los cultivos forestales con destinacion energetica se han ido posicionando como una alternativa viable para la diversificacion de la matriz energetica del pais. Este tipo de cultivos, aun en fase de desarrollo, se basan en turnos cortos de rotacion con altas producciones de biomasa. El problema surge a la hora de evaluar la sostenibilidad de dichos cultivos. El calculo del balance energetico es clave para valorar dicha sostenibilidad, es decir, no se puede gastar mas energia en producir biomasa que la que esta otorga con la combustion. En este trabajo se calcula el balance energetico, considerando los productos de la cosecha puestos a orilla de camino, de un cultivo de Populus deltoides clon Lux con fines energeticos durante un periodo de ocho anos (2000-2008), comparando un turno de rotacion bienal (T2) con uno trienal (T3) en un sitio con ambiente mediterraneo. Para ello se ha calculado el costo energetico de la produccion y cosecha, y la cantidad de energia liberada en la combustion de la biomasa generada. En ambos turnos de rotacion se obtienen resultados positivos, siendo mas conveniente energeticamente el turno trienal respecto al bienal (34,7 T2 vs 25 T3).