Greenhouse gas emission reductions in subtropical cereal-based cropping sequences using legumes, DMPP-coated urea and split timings of urea application

To contribute to national greenhouse gas emissions (GHG) reduction targets, grain growers need strategies that minimise emissions associated with grain production. We used life cycle assessments (LCAs) with field-measured production inputs, grain yields and proteins, legume nitrogen ([N.sub.2]) fixation, and soil nitrous oxide ([N.sub.2]0) and methane (C[H.sub.4]) emissions, to explore mitigation strategies in 3-year crop sequences in subtropical Australia. The sequences were: canola plus 80 kg/ha fertiliser nitrogen (80N)-wheat 85N-barley 65N ([Ca.sub.N][Wt.sub.N][Ba.sub.N]), chickpea ON-wheat 85N-barley 5N ([Cp.sub.N][Wt.sub.N]Ba), chickpea ON-wheat 5N-chickpea 5N (CpWtCp), and chickpea ON-sorghum 45N (CpSgN). We also assessed the impacts of split fertiliser N application and urea coated with DMPP, a nitrification inhibitor, on the LCA for the [Ca.sub.N][Wt.sub.N][Ba.sub.N] sequence.Total pre-farm plus on-farm GHG emissions varied between 915 C[O.sub.2]-e/ha (CpSgN) and 1890 C[O.sub.2]-e/ha ([Ca.sub.N][Wt.sub.N][Ba.sub.N]). Cumulative [N.sub.2]O emitted over the 3-year study varied between 0.479 kg [N.sub.2]O-N/ha (CpWtCp) and 1.400 kg [N.sub.2]O-N/ha ([Ca.sub.N][Wt.sub.N][Ba.sub.N]), which constituted 24 44% of total GHG emissions. Fertiliser production accounted for 20% (CpSgN) to 30% ([Ca.sub.N][Wt.sub.N][Ba.sub.N]) of total emissions. An extra 4.7 kg C[O.sub.2]-e/ha was emitted for each additional kg N/ha of applied N fertiliser. Three-year CH4 emissions ranged from -1.04 to -0.98 kg CH4-C/ha. Split N and DMPP strategies could reduce total GHG emissions of [Ca.sub.N][Wt.sub.N][Ba.sub.N] by 17 and 28% respectively. Results of the study indicate considerable scope for reducing the carbon footprint of subtropical, dryland grains cropping in Australia.Additional keywords: carbon dioxide, carbon footprint, fertiliser N, grain cropping, greenhouse gas emissions, life cycle assessment, methane, nitrous oxide.
IntroductionQuantification of anthropogenic greenhouse gas (GHG) emissions from agriculture, specifically nitrous oxide ([N.sub.2]O), methane (C[H.sub.4]), and carbon dioxide (C[O.sub.2]), at scales from national inventories to individual fields reflects concern about [...]