Fertilizer use, biofuel energy balance and GHG emissions

Energy balances and Greenhouse Gas (GHG) emission reduction from biofuel production in the Netherlands was evaluated using a tool developed by Wageningen University and Research Centre and Biomass Research. The model (Energy Crop Simulation Model or E-CROP) covers the entire biofuel production chain from sowing to distribution. A recent paper describes E-CROP application to four crops on two sites in the Netherlands (potato and sugar beet for bioethanol, winter oilseed rape for biodiesel and silage maize for bioelectricity) and on the effect of crop management (irrigation and nitrogen fertilisation).

In all situations, gross energy output exceeded total energy input. Average net energy yield ranged from 45 to 140 GJ∙ha. Net reduction of GHG emissions ranged from 0.60 to 6.5 t CO2-eq per hectare. N2O emission from nitrogen fertiliser caused large variations in the net reduction of GHG emissions, which may be reduced to zero.

Reducing irrigation or fertilisation  caused large variations in the net GHG reduction, which even might become negative. Low nitrogen fertilizer applications reduced yield levels but enhanced net GHG emission reduction. It is concluded that good knowledge of agricultural practices is needed if one wants to optimise the performance of bioenergy production.

The study was done following ISO 14040/44 guidelines for Life Cycle Assessment (LCA). The goal of the analysis was to evaluate the effects of biofuel chain and crop management options with respect to the potential of energy crops to replace non-renewable (fossil) energy and to reduce GHG emissions. Bioenergy chains were compared in a “Well to Tank” analysis with their appropriate fossil reference chains (bioethanol −> gasoline from crude oil, biodiesel −> diesel from crude oil, bio-electricity −> power production from a mix of fuels and heat −> heat production from natural gas). Co-products from cropping and biofuel production were either incorporated into the soil or converted into additional energy, e.g., electricity, of which the benefits were added to the energy and GHG emission balances.

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