181. Soil carbon sequestration rates and associated economic costs for farming systems of South-Eastern Australia

• Authors:
  • Antle, J.
  • Ogle, S.
  • Paustian, K.
  • Basso, B.
  • Grace, P. R.
• Source: Australian Journal of Soil Research
• Volume: 48
• Issue: 8
• Year: 2010

182. Nitrous oxide emissions from irrigated cotton soils of northern Australia

• Authors:
  • Grace, P.
  • Kiese, R.
  • Butterbach-Bahl, K.
  • Rowlings, D.
  • Rochester, I.
• Source: Soil Solutions for a Changing World: proceedings of the 19th World Congress of Soil Science
• Year: 2010

183. Soil nitrous oxide and methane fluxes are low from a bioenergy crop (canola) grown in a semi-arid climate

• Authors:
  • Barton, L.
  • Murphy, D. V.
  • Kiese, R.
  • Butterbach-Bahl, K.
• Source: GCB Bioenergy
• Volume: 2
• Issue: 1
• Year: 2010
• Summary: Understanding nitrous oxide (N2O) and methane (CH4) fluxes from agricultural soils in semi-arid climates is necessary to fully assess greenhouse gas emissions from bioenergy cropping systems, and to improve our knowledge of global terrestrial gaseous exchange. Canola is grown globally as a feedstock for biodiesel production, however, resulting soil greenhouse gas fluxes are rarely reported for semi-arid climates. We measured soil N2O and CH4 fluxes from a rain-fed canola crop in a semi-arid region of south-western Australia for 1 year on a subdaily basis. The site included N fertilized (75 kg N ha−1 yr−1) and nonfertilized plots. Daily N2O fluxes were low (−1.5 to 4.7 g N2O-N ha−1 day−1) and culminated in an annual loss of 128 g N2O-N ha−1 (standard error, 12 g N2O-N ha−1) from N fertilized soil and 80 g N2O-N ha−1 (standard error, 11 g N2O-N ha−1) from nonfertilized soil. Daily CH4 fluxes were also low (−10.3 to 11.9 g CH4-C ha−1 day−1), and did not differ with treatments, with an average annual net emission of 6.7 g CH4–C ha−1 (standard error, 20 g CH4–C ha−1). Greatest daily N2O fluxes occurred when the soil was fallow, and following a series of summer rainfall events. Summer rainfall increased soil water contents and available N, and occurred when soil temperatures were >25 °C, and when there was no active plant growth to compete with soil microorganisms for mineralized N; conditions known to promote N2O production. The proportion of N fertilizer emitted as N2O, after correction for emissions from the no N fertilizer treatment, was 0.06%; 17 times lower than IPCC default value for the application of synthetic N fertilizers to land (1.0%). Soil greenhouse gas fluxes from bioenergy crop production in semi-arid regions are likely to have less influence on the net global warming potential of biofuel production than in temperate climates.

184. Options for the abatement of methane and nitrous oxide from ruminant production: A review

• Authors:
  • de Klein, C. A. M.
  • Grainger, C.
  • Eckard, R. J.
• Source: Livestock Science
• Volume: 130
• Year: 2010

185. Greenhouse gas emissions from intensive pasture on ferrosol in Northern NSW, Australia: Impact of biochar amendment

• Authors:
  • Van Zwieten, L.
  • Kimber, S.
  • Rowling, D.
  • Grace, P. R.
  • Scheer, C.
• Source: Soil Solutions for a Changing World
• Year: 2010
• Summary: An intensive field campaign was performed from April to June 2009 to assess the effect of biochar amendment on the emission of soil-borne GHGs from a sub-tropical pasture on acidic ferrosol. Over the whole measurement period high emissions of N2O and high fluxes of CO2 could be observed, whereas a net uptake of CH4 was measured. Only small differences in the fluxes of N2O and CH4 from the biochar amended plots (35.33 ± 4.83 μg N2O-N/m2/h, -6.76 ± 0.20 μg CH4 -C/m2/h) vs. the control plots (31.08 ± 3.50 μg N2O-N/m2/h, -7.30 ± 0.19 μg CH4 -C/m2/h) could be observed, while there was no significant difference in the fluxes of CO2. However, it could be observed that N2O emissions were significantly lower from the biochar amended plots during periods with low emission rates (< 50 μg N2O-N/m2/h). Only during an extremely high emission event following heavy rainfall N2O emissions from the biochar amended plots were higher than from the control plots. Our results demonstrate that pastures on ferrosols in Northern NSW are a significant source of GHG and that the amendment of biochar can alter those emissions. However, more field and laboratory incubation studies covering prolonged observation periods are needed to clarify the impact of biochar amendment on soil microbial processes and the emission of soil-borne GHGs.

186. Comparison of the ability of the nitrification inhibitors DCD and DMPP to reduce nitrification and N<SUB>2</SUB>O emissions from nitrogen fertilisers

• Authors:
  • Walker, C.
  • Edis, R.
  • Li, H.
  • Chen, D.
  • Suter, H.
• Source: Soil Solutions for a Changing World
• Year: 2010

187. Reducing N<SUB>2</SUB>O emissions from nitrogen fertilisers with the nitrification inhibitor DMPP

• Authors:
  • Walker, C.
  • Edis, R.
  • Li, H.
  • Chen, D.
  • Suter, H.
• Source: Soil Solutions for a Changing World
• Year: 2010

188. Influence of biochars on flux of N<SUB>2</SUB>O and CO<SUB>2</SUB> from ferrosol

• Authors:
  • Scheer, C.
  • Rust, J.
  • Berger, E.
  • Downie, A.
  • Morris, S.
  • Kimber, S.
  • Van Zwieten, L.
• Source: Australian Journal of Soil Research
• Volume: 48
• Issue: 7
• Year: 2010
• Summary: Biochars produced by slow pyrolysis of greenwaste (GW), poultry litter (PL), papermill waste (PS), and biosolids (BS) were shown to reduce N2O emissions from an acidic Ferrosol. Similar reductions were observed for the untreated GW feedstock. Soil was amended with biochar or feedstock giving application rates of 1 and 5%. Following an initial incubation, nitrogen (N) was added at 165 kg/ha as urea. Microcosms were again incubated before being brought to 100% water-filled porosity and held at this water content for a further 47 days. The flooding phase accounted for the majority (<80%) of total N2O emissions. The control soil released 3165 mg N2O-N/m2, or 15.1% of the available N as N2O. Amendment with 1 and 5% GW feedstock significantly reduced emissions to 1470 and 636 mg N2O-N/m2, respectively. This was equivalent to 8.6 and 3.8% of applied N. The GW biochar produced at 350°C was least effective in reducing emissions, resulting in 1625 and 1705 mg N2O-N/m2 for 1 and 5% amendments. Amendment with BS biochar at 5% had the greatest impact, reducing emissions to 518 mg N2O-N/m2, or 2.2% of the applied N over the incubation period. Metabolic activity as measured by CO2 production could not explain the differences in N2O emissions between controls and amendments, nor could NH4+ or NO3– concentrations in biochar-amended soils. A decrease in NH4+ and NO3– following GW feedstock application is likely to have been responsible for reducing N2O emissions from this amendment. Reduction in N2O emissions from the biochar-amended soils was attributed to increased adsorption of NO3–. Small reductions are possible due to improved aeration and porosity leading to lower levels of denitrification and N2O emissions. Alternatively, increased pH was observed, which can drive denitrification through to dinitrogen during soil flooding.

189. Assessment of the boundary line approach for predicting N<SUB>2</SUB>O emission ranges from Australian agricultural soils

• Authors:
  • Dalal, R. C.
  • Wang, W. J.
• Source: Soil Solutions for a Changing World
• Year: 2010
• Summary: This study aimed to assess the feasibility of predicting ranges in N2O emission with a boundary line approach using a few key driving factors. Intact soil cores (9 cm dia. and ~20 cm in depth) were collected from pasture, cereal cropping and sugarcane lands and incubated at various temperature and moisture conditions after addition of different forms of mineral nitrogen (NH4+ and NO3⎯). The pasture and sugarcane soils showed greater N2O production capacity than the cropping soils with similar mineral N and organic C contents or under similar temperature and water filled pore space (WFPS%), and thus different model parameters need to be used. The N2O emission rates were classified into three ranges: low (< 16 g N2O/ha/day), medium (16 –160 g N2O/ha/day) and high (> 160 g N2O/ha/day). The results indicated that N2O emissions were in the low range when soil mineral N content was below 10 mg N/kg for the cropping soils and below 2 mg N/kg for the pasture and sugarcane soils. In soils with mineral N content exceeding the above thresholds, the emission rates were largely regulated by soil temperature and WFPS and the emission ranges could be estimated using linear boundary line models that incorporated both temperature and WFPS. Using these key driving factors (land use, temperature, WFPS and mineral N content), the boundary line models correctly estimated the emission ranges for 85% of the 247 data points for the cropping soils and 59% of the 271 data points for the pasture and sugarcane soils. In view of the fact that N2O emissions from soil are often very variable and difficult to predict and that the soil and environmental conditions applied in this study differed substantially, the above results suggested that, in terms of accuracy and feasibility, the boundary line approach provides a simple and practical alternative to the use of a single emission factor and more complex process-based models.

190. Biofuels agriculture: landscape-scale trade-offs between fuel, economics, carbon, energy, food, and fiber

• Authors:
  • Bryan, B. A.
  • King, D.
  • Wang, E.
• Source: Global Change Biology Bioenergy
• Volume: 2
• Issue: 6
• Year: 2010
• Summary: First-generation biofuels are an existing, scalable form of renewable energy of the type urgently required to mitigate climate change. In this study, we assessed the potential benefits, costs, and trade-offs associated with biofuels agriculture to inform bioenergy policy. We assessed different climate change and carbon subsidy scenarios in an 11.9 million ha (5.48 million ha arable) region in southern Australia. We modeled the spatial distribution of agricultural production, full life-cycle net greenhouse gas (GHG) emissions and net energy, and economic profitability for both food agriculture (wheat, legumes, sheep rotation) and biofuels agriculture (wheat, canola rotation for ethanol/biodiesel production). The costs, benefits, and trade-offs associated with biofuels agriculture varied geographically, with climate change, and with the level of carbon subsidy. Below we describe the results in general and provide (in parentheses) illustrative results under historical mean climate and a carbon subsidy of A$20 t−1 CO2−e. Biofuels agriculture was more profitable over an extensive area (2.85 million ha) of the most productive arable land and produced large quantities of biofuels (1.7 GL yr−1). Biofuels agriculture substantially increased economic profit (145.8 million $A yr−1 or 30%), but had only a modest net GHG abatement (−2.57 million t CO2−e yr−1), and a negligible effect on net energy production (−0.11 PJ yr−1). However, food production was considerably reduced in terms of grain (−3.04 million t yr−1) and sheep meat (−1.89 million head yr−1). Wool fiber production was also substantially reduced (−23.19 kt yr−1). While biofuels agriculture can produce short-term benefits, it also has costs, and the vulnerability of biofuels to climatic warming and drying renders it a myopic strategy. Nonetheless, in some areas the profitability of biofuels agriculture is robust to variation in climate and level of carbon subsidy and these areas may form part of a long-term diversified mix of land-use solutions to climate change if trade-offs can be managed.