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Several studies suggest that lignocellulosic energy crops for electricity production may have a better performance compared to those crops for liquid biofuels production, when assessing GHG savings with respect to fossil references. Winter cereal residues and some annual winter grasses, as dedicated energy crops, are currently being grown in Spain and harvested as bales to be burned for electricity production in biomass power plants. Previous studies of our group analyzed GHG emissions and energy balances of winter cereals for electricity production by means of Life Cycle Assessment. We selected highly productive genotypes of three annual winter cereals (rye, triticale and oat) and compared them with Spanish electricity produced using natural gas. This paper compares effects of the use of different crop management practices for rye growing in the assessment of energy balances and GHG emissions. We analyzed the effects of six different management practices consisting of two different sowing doses (suboptimal and normal) combined with three top fertilization doses (zero, 30 and 80kgN ha-1). We made a characterization analysis of biomasses to estimate the nitrogen uptake of the crops in order to compare it with the nitrogen provided by the fertilizers. This comparison evaluates if lower fertilization doses are sustainable for the soil nitrogen stocks. Our results suggest that there is trade-off between soil nitrogen and emission savings. The use of zero or low top fertilization doses (30 kg N ha-1) improves GHG emissions and energy balances even with a yield reduction. Nevertheless the use of these doses imply an annual lose in soil nitrogen stocks for the majority all of our trials. Using suboptimal sowing doses resulted in yield decreases that did not compensate the lower input consumed.
Keywords: electricity, energy balance, energy crops, greenhouse gases (GHG), life cycle assessment (LCA), sustainability criteria