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Wang W.,Information Technology and Innovation DSITI | Wang W.,Griffith University | Dalal R.C.,Information Technology and Innovation DSITI
European Journal of Agronomy | Year: 2015

Farm management affects the global greenhouse gas (GHG) budget by changing not only soil organic carbon (SOC) stocks and nitrous oxide (N2O) emissions but also other pre-farm, on-farm and off-site emissions. The life cycle assessment (LCA) approach has been widely adopted to assess the "carbon footprint" of agricultural products, but rarely used as a tool to identify effective mitigation strategies. In this study, the global warming impacts of no-till (NT) vs. conventional till (CT), stubble retention (SR) vs. stubble burning (SB), and N fertilization (NF) vs. no N fertilization (N0) in an Australian wheat cropping system were assessed using in situ measurements of N2O fluxes over three years, SOC changes over forty years and including other supply chain GHG sources and sinks. The results demonstrated the importance of full GHG accounting compared to considering SOC changes or N2O emissions alone for assessing the global warming impacts of different management practices, and highlighted the significance of accurately accounting for SOC changes and N2O emissions in LCAs. The GHG footprints of wheat production were on averaged 475kg carbon dioxide equivalent (CO2-e) ha-1 (or 186kg CO2-e t-1 grain) higher under NF than N0. Where fertilizer N was applied (70kgNha-1), the life cycle emissions were 200kg CO2-e ha-1 (or 87t-1 grain) lower under NT than CT and 364kg CO2-e ha-1 (or 155t-1 grain) lower under SR than SB. Classification of the emission sources/sinks and re-calculation of published data indicated that under the common practices of SR combined with NT, N-related GHG emissions contributed 60-95% of the life cycle emissions in the predominantly rain-fed wheat production systems in Australia. Therefore, future mitigation efforts should aim to improve N use efficiency, explore non-synthetic N sources, and most importantly avoid excessive N fertilizer use whilst practising NT and SR. © 2015 Elsevier B.V. Source

Rezaei Rashti M.,Information Technology and Innovation DSITI | Rezaei Rashti M.,Griffith University | Wang W.J.,Information Technology and Innovation DSITI | Wang W.J.,Griffith University | And 5 more authors.
Soil Research | Year: 2015

The greenhouse gas fluxes and effective mitigation strategies in subtropical vegetable cropping systems remain unclear. In this field experiment, nitrous oxide (N2O) and methane (CH4) fluxes from an irrigated lettuce cropping system in subtropical Queensland, Australia, were measured using manual sampling chambers. Four treatments were included: Control (no fertiliser), U100 (100kg N ha-1 as urea), U200 (200kg N ha-1 as urea) and N100 (100kg N ha-1 as nitrate-based fertilisers). The N fertilisers were applied in three splits and irrigation was delivered sparingly and frequently to keep soil moisture around the field capacity. The cumulative N2O emissions from the control, U100, U200 and N100 treatments over the 68-day cropping season were 30, 151, 206 and 68g N2O-N ha-1, respectively. Methane emission and uptake were negligible. Using N2O emission from the Control treatment as the background emission, direct emission factors for U100, U200 and N100 treatments were 0.12%, 0.09% and 0.04% of applied fertiliser N, respectively. Soil ammonium (NH4+) concentration, instead of nitrate (NO3-) concentration, exhibited a significant correlation with N2O emissions at the site where the soil moisture was controlled within 50%-64% water-filled pore space. Furthermore, soil temperature rather than water content was the main regulating factor of N2O fluxes in the fertilised treatments. Fertiliser type and application rates had no significant effects on yield parameters. Partial N balance analysis indicated that approximately 80% and 52% of fertiliser N was recovered in plants and soil in the treatments receiving 100kg N ha-1 and 200kg N ha-1, respectively. Therefore, in combination with frequent and low-intensity irrigation and split application of fertiliser N, substitution of NO3-based fertilisers for urea and reduction in fertiliser N application rates were considered promising mitigation strategies to maintain yield and minimise N2O emissions during the low rainfall season. © 2015 CSIRO. Source

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