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In an emission intensive era, renewable energy resources, like second-generation lignocellulosic biofuels, offer a solution to reduce our global reliance on fossil fuels and mitigate greenhouse gas (GHG) emissions. Willow short rotation plantations are particularly effective non-food biofuels that can be grown on marginal lands. This ensures that agricultural land is not seized for biofuel growth, and prevents food crops from feeding fuel tanks rather than people. Overall, these plantations are an effective biofuel option relative to first generation options like corn-based ethanol. Arguably, the most important objective of lignocellulosic biofuels is that they are carbon (C)-neutral energy sources. After all, one of the main problems with burning fossil fuels is the release of GHG into the atmosphere, which accelerates climate change.

WillowBiomassPlantation
Willow biomass plantation at the Guelph Turfgrass Institute in Guelph, Ontario, Canada.

In theory, C that is taken up through willow photosynthesis and growth offsets the C that is released through biofuel production and consumption. However, the GHG budget does not solely depend on the difference between C sequestered in vegetation versus the C that is released by biofuel burning. The net GHG budget is much more complex, and depends on the emissions that are released throughout the whole life cycle of the plant, including land management.

One management practice that affects the GHG emissions from willow biomass plantations is the application of nitrogen (N) fertilizer. Fertilizer can increase biomass growth, especially in N limited temperate soils. However, N fertilizer application may also be associated with environmental disservices. This is because N fertilizer application can alter C and N cycling in the soil and may result in elevated CO2 and N2O emissions, both of which are powerful GHGs. Without considering the effect of fertilizer application on both of these GHGs, there may be an overestimation of net GHG reductions, and sources of lignocellulosic biofuels from willow biomass plantations may not be C neutral.

A project conducted at the University of Guelph Turfgrass Institute, Guelph, Ontario, Canada, aims to determine the effect of N fertilizer application on willow biomass plantations. Information about this effect, used in conjunction with biomass data from the harvest and quantified soil characteristics, allows us to determine if productivity gains are worth the immediate increase of N2O emissions that is produced from N fertilizer application.
 
Initial results have shown that CO2 emissions are more dependent on seasonal changes in soil temperature and moisture patterns. Generally, they are the highest in the summer months. N2O emissions are greatly affected by fertilizer application. This is problematic because these emissions, with a global warming potential that is 296 times greater than that of C, deplete stratospheric ozone. The study’s results will be compared to biomass data from the most recent willow harvest in December of 2015, to determine the costs and benefits associated with N fertilizer application in willow biomass production systems. Most recent results were published in: Lutes, K. et al. 2016. Effect of nitrogen fertilizer on greenhouse gas emissions in two willow clones (Salix miyabeana and S. dasyclados) in southern Ontario, Canada. Agroforestry Systems DOI 10.1007/s10457-016-9897-z.