Life cycle assessment of oilseed crops produced in rotation with dryland cereals in the inland Pacific Northwest

Purpose Oilseed crops are expected to become an important feedstock for production of renewable jet fuel. The objective of this study is to determine the life cycle energy and greenhouse gas (GHG) emissions of several 2- and 3-year crop rotations with cereals and oilseeds in a low precipitation environment of the inland Pacific Northwest. The purpose is to ascertain whether cropping intensification could improve energy efficiency and reduce GHG emissions. Methods A life cycle assessment (LCA) was carried out to evaluate the fossil energy and carbon footprint of nine cropping systems characterized by different inputs applied to spring carinata [Brassica carinata (A.) Braun] and winter canola (B. napus L.) in rotation with wheat (Triticum aevistum L.) and other cereal crops. Grain yield and field activity data from cropping systems were acquired from a field experiment over a 5-year period. Gas emissions were measured weekly over 2 years using static chamber methodology and laboratory gas chromatography. Inputs for the LCA regarding fertilizers, machinery fuel use, and pesticides were from the field trials and literature for fuel use. Results and discussion Emission results of winter wheat (WW) rotations are between 300 and 400 g CO2 eq. kg−1 WW, in the range for US average WW cropping emissions (i.e., 300–600 g CO2 eq. kg−1 WW). Reduced tillage fallow (RTF)-Winter oilseed (WO)-RTF-WW and summer fallow (SF)-WW rotation were the most promising, from a trade-off of GHG emissions versus total crop sales over 6 years per hectare with low emissions and high sales. The best oilseed result was 660 g CO2 eq. kg−1 for canola following RTF. Highest yields were observed when cereal or oilseed crops were planted following RTF. Efficiency in terms of Energy Return on Energy Investment was 3.85 for winter oilseed yields 1338.9 kg ha−1 and 1.6 for spring oilseed yields 552.2 kg ha−1. Conclusions Compared to SF-WW, bioenergy oilseed cultivation may increase CO2 equivalent emissions in 3-year cereal-based rotations due to increased inputs with inclusion of fallow-substitution cultivation. Fossil energy inputs required to produce oilseed crops were smaller than the total energy in final seed and thus oilseeds have the potential to reduce reliance on fossil fuels. Improving energy efficiency and encouraging adoption by growers will depend on ability to enhance agronomic performance with higher yielding, drought and cold tolerant oilseed varieties