Economic, energetic and environmental impact in short rotation coppice harvesting operations

In Italy, agro-energy’s contribution to the national primary energy demand is still moderate. Among the energy crops Short Rotation Coppice (SRC) has taken up about 6500 ha, using poplar clones. For this crop, the harvesting operations, usually, are carried out by modified forage harvester equipped with dedicated headers and by tractor coupled with trailers. This, besides the high economic costs, involves also energy inputs and green house gas (GHG) emissions that must be carefully taken in account when the sustainability of the whole agro-energy chain is assessed. This study shows the results of filed tests carried out on 69.2 ha of biennial SRC with two different poplar plantation systems. Yield ranges from 16.7 to 33.71 tdm/ha (dry matter), chip moisture content between 50.4 and 64.8% and bulk density between 118.8 and 169.2 kgdm/m3. Effective field capacity and theoretical field capacity are highly variable, respectively, from 0.77 to 1.67 ha/h and from 1.18 to 2.15 ha/h. Economic cost, energetic input and GHG emissions depend on yield, annual use of the machines and scheduling of operations. The analysis shows that the best performances are achieved when harvest and transport are carried out on a area upper than 400 ha, with an efficient plantation design, a proper-sized transport system and without mechanical failures. In these case the productivity of the harvest-transport system can arrive at 65 twb/h (wet basis) while the economic cost, the energetic input and the GHG emissions reach, respectively, 15 €/tdm, 212 MJ/tdm and 16 kgCO2eq/tdm.

► The harvest with a header prototype was tested in different SRC plantations.
► The prototype was able to harvest plantations with different plant density.
► Theoretical and Effective field capacity are variable depending on harvest conditions.
► The lower costs can be achieved when harvest is carried out over large area.
► Energetic costs of harvest operations corresponds to 3–4% of the LHV of the chips.