• Authors:
    • Mosier, A. R.
    • Chen, D.
    • Lam, S. K.
    • Roush, R.
  • Source: Scientific Reports
  • Volume: 3
  • Issue: July
  • Year: 2013
  • Summary: Concerns about increasing concentrations of greenhouse gases in the atmosphere, primarily carbon dioxide (CO2), have raised worldwide interest in the potential of agricultural soils to be carbon (C) sinks. In Australia, studies that have quantified the effects of improved management practices in croplands on soil C have generally been inconclusive and contradictory for different soil depths and durations of the management changes. We therefore quantitatively synthesised the results of Australian studies using meta-analytic techniques to assess the technical and economic feasibility of increasing the soil C stock by improved management practices. Our results indicate that the potential of these improved practices to store C is limited to the surface 0-10 cm of soil and diminishes with time. None of these widely adopted practices is currently financially attractive under Australia's new legislation known as the Carbon Farming Initiative.
  • Authors:
    • Armstrong, R.
    • Norton, R.
    • Chen, D.
    • Lam, S. K.
  • Source: Plant and Soil
  • Volume: 364
  • Issue: 1-2
  • Year: 2013
  • Summary: This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO2]). Field pea (Pisum sativum L.) was labeled in situ with N-15 (by absorption of a N-15-labeled urea solution through cut tendrils) under ambient and elevated (700 mu mol mol(-1)) [CO2] in controlled environment glasshouse chambers. Barley (Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of N-15-enriched urea to the soil. Wheat (Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either N-15-labeled field pea residues (including N-15-labeled rhizodeposits) or N-15-labeled barley plus fertilizer N-15 residues. Elevated [CO2] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO2] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO2] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO2], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO2], but dropped to 11 % under elevated [CO2], while that from fertilizer did not differ significantly between ambient [CO2] (4 %) and elevated [CO2] (5 %). The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO2]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO2]) climates.
  • Authors:
    • Fest, B. J.
    • Idczak, D.
    • Livesley, S. J.
  • Source: Science of The Total Environment
  • Volume: 465
  • Issue: November
  • Year: 2013
  • Summary: National and regional C emissions from historical land use change (LUC) and fossil fuel use are proposed as a basis to ascribe 'burden-sharing' for global emission reduction targets. Changes in non-CO2 greenhouse gas emissions as a result of LUC have not been considered, but may be considerable. We measured soil-atmosphere exchange of methane (CH4) and nitrous oxide (N2O) in remnant forest, pasture and viticulture systems in four seasons, as well as differences in soil C density and the C density of remnant forest vegetation. This approach enabled comparative assessment of likely changes in ecosystem C density and soil non-CO2 greenhouse gas exchange along a LUC continuum since European settlement. Soil CH4 uptake was moderate in forest soil (-27 mu g C m(-2) h(-1)), and significantly different to occasionally large CH4 emissions from viticulture and pasture soils. Soil N2O emissions were small and did not significantly differ. Soil C density increased significantly with conversion from forest (5 kg m(-2)) to pasture (9 kg m(-2)), and remained high in viticulture. However, there was a net decrease in ecosystem C density with forest conversion to pasture. Concurrently, net soil non-CO2 emissions (CH4 and N2O combined) increased with conversion from forest to pasture. Since European settlement 170 years ago, it was estimated similar to 8114 Gg CO2-e has been released from changes in ecosystem C density in the Mornington Peninsula, whereas similar to 383 Gg CO2-e may have been released from changes in soil non-CO2 exchange processes. Principally, a switch from soil CH4 uptake to soil CH4 emission after forest clearing to agro-pastoral systems provided this further similar to 5% contribution to the historical landscape CO2-e source strength. Conserving and restoring remnant forests and establishing new tree-based systems will enhance landscape C density. Similarly, minimising anaerobic, wet conditions in pasture/viticulture soils will help reduce non-CO2 greenhouse gas emissions. (C) 2013 Elsevier B.V. All rights reserved.
  • Authors:
    • Reardon-Smith, K.
    • Maraseni, T. N.
    • Mushtaq, S.
  • Source: Agricultural Systems
  • Volume: 117
  • Year: 2013
  • Summary: There are significant concerns about the longer term impact of climate change and climate variability on water availability in Australia. Modern irrigation technologies are seen as a way to manage climate change impacts and improve water security. However, while modern irrigation technologies may save volumes of water, it is likely that they will result in increased on-farm energy consumption and greenhouse gas (GHG) emissions, suggesting potential conflicts in terms of mitigation and adaptation policies. Five irrigation technology transformation scenarios-three historical and two adoption-were developed to evaluate industry-wide tradeoffs between water savings, energy consumption (and GHG emissions), and economic returns associated with irrigation technology transformations under current Australian Government water resource policies. Three of the five scenarios tested showed tradeoffs between water savings and GHG emissions, with water savings through conversion of irrigation systems increasing both energy consumption and GHG emissions. For example, 120 GL/year of water savings achieved through drip irrigation adoption for cotton cropping would increase energy consumption by 889 TJ/year and GHG emissions by 250,000 t CO(2)e/year. A carbon price of $20/t CO(2)e would result in additional costs nationally of about $5 m/year. However, this study also indicated that significant benefit in terms of water savings and GHG reduction can be achieved when replacing older inefficient and energy-intensive systems, such as hand shift and roll-line sprinkler systems, especially when these are replaced with drip irrigation systems. We suggest priority should be given to replacing such systems while implementing the on-farm infrastructure investment policy. The findings of the study support the use of an integrated approach to avoid possible conflicts in designing national climate change mitigation and adaptation policies, both of which are being developed in Australia.
  • Authors:
    • Robertson, F.
    • Nash, D.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 165
  • Year: 2013
  • Summary: The extent to which soil C storage can be increased in Australian agricultural soils by adoption of improved management practices is poorly understood. There is a pressing need for such information in order to evaluate the potential for soil C sequestration to offset greenhouse gas emissions. In this study we used the RothC model to assess whether soil C accumulation under cropping using stubble retention and pasture rotations could be a significant offset for greenhouse gas emissions. We chose eight regions to represent the climatic range of the Victorian cropping industry: Walpeup, Birchip, Horsham, Bendigo, Rutherglen, Lismore, Bairnsdale and Hamilton (annual rainfall 330-700 mm). For each region, we chose two representative soil types, varying in clay and total organic C contents. For each region x soil combination, we compared the effects of five rotations: Canola-wheat-pulse-barley (C-W-P-B); Canola-wheat-triticale (C-W-T); Canola-wheat-barley-5 year perennial pasture (C-W-B-Pt5); Canola-wheat-fallow (C-W-F) and Continuous pasture (Pt). We compared the cropping rotations with cereal stubble burnt and with cereal stubble retained and, for two regions, with cereal stubble grazed by sheep. The results of the simulations showed that, across all scenarios, the equilibrium C density varied between 19 and 135 t C/ha to 300 mm depth, with potential soil C change being strongly influenced by crop yield, crop rotation, climate, initial soil C content, stubble management and continuity of management The simulations suggested that soil C stocks could be increased under a crop-pasture rotation (C-W-B-Pt5) with stubble retention, with rates of increase of 0.3-0.9 t C/ha yr over 25 years. If all of Victoria's cropland were converted to C-W-B-Pt5 rotation with stubble retention, and if 50% of the modelled potential C change were achieved, this would represent 3.0-4.5 MtCO(2)-e/year, equivalent to 2.5-3.7% of Victoria's greenhouse emissions. Less C accumulation would be possible under continuous cropping with stubble retention; even using the most conservative rotation (C-W-T) rates of C change varied from loss of 0.3 t C/ha yr to accumulation of 0.5 t C/ha yr over 25 years. If all of Victoria's cropland were converted to C-W-T rotation with stubble retention, and if 50% of the modelled potential C change were achieved, this would be equivalent to 0.8-2.3 MtCO(2)-e/year, or 0.7-1.9% of Victoria's greenhouse emissions. It would generally take 10-25 years for the soil C changes to become measurable using conventional soil sampling and analytical methods. Thus we conclude that, with current technology, the potential for significant and verifiable soil C accumulation in Victoria's croplands is limited.
  • Authors:
    • Thorburn, P.
    • Ruane, A.
    • Marin, F.
    • Jones, M.
    • Singels, A.
  • Source: An International Journal of Sugar Crops and Related Industries
  • Volume: 115
  • Issue: 1380
  • Year: 2013
  • Summary: Future climate change is expected to have important consequences for sugarcane production, and reliable predictions of crop response to climate change are necessary to plan adaptation strategies. The objective of this study was to assess the use of global climate models (GCMs) and a crop simulation model for predicting climate change impacts on sugarcane production. The Canegro model was used to simulate growth and development of sugarcane crops under typical management conditions at three sites (irrigated crops at Ayr, Australia; rainfed crops at Piracicaba, Brazil and La Mercy, South Africa) for current and three future climate scenarios. The baseline scenario consisted of a 30-year time series of historical daily weather records and atmospheric CO2 concentration ([CO2]) set at 360 ppm. Future climate scenarios were derived from three GCMs for the A2 greenhouse gas emission scenario and [CO2] set at 734 ppm. The three GCMs were chosen to represent the uncertainty in projected rainfall changes. Future cane yields are expected to increase at all three sites, ranging from +4% for Ayr, to +9% and +20% for Piracicaba and La Mercy. The uncertainty of these predictions correlates with the magnitude of the predicted yield increase. Canopy development was accelerated at all three sites by increased temperature, which led to increased interception of radiation, increased transpiration, and slight increases in drought stress at rainfed sites. For the high potential sites (Ayr and Piracicaba), yield increases were limited by large increases in maintenance respiration which consumed most of the daily assimilate when high biomass was achieved. A weakness of the climate data used was the assumption of no change in rainfall distribution, solar radiation and relative humidity-variables that are crucial in determining the water status of rainfed sugarcane. Crop model aspects that need refinement include improved simulation of (1) elevated [CO2] effects on crop photosynthesis and transpiration, and (2) high temperature effects on crop development, photosynthesis and respiration.
  • Authors:
    • Tausz, M.
    • Norton, R. M.
    • Cane, K.
    • Tausz-Posch, S.
    • Thilakarathne, C. L.
    • Seneweera, S.
  • Source: Functional Plant Biology
  • Volume: 40
  • Issue: 2
  • Year: 2013
  • Summary: In order to investigate the underlying physiological mechanism of intraspecific variation in plant growth and yield response to elevated CO2 concentration [CO2], seven cultivars of spring wheat (Triticum aestivum L.) were grown at either ambient [CO2] (similar to 384 mu mol mol(-1)) or elevated [CO2] (700 mu mol mol(-1)) in temperature controlled glasshouses. Grain yield increased under elevated[CO2] by an average of 38% across all seven cultivars, and this was correlated with increases in both spike number (productive tillers) (r = 0.868) and aboveground biomass (r = 0.942). Across all the cultivars, flag leaf photosynthesis rate (A) increased by an average of 57% at elevated [CO2]. The response of A to elevated [CO2] ranged from 31% (in cv. H45) to 75% (in cv. Silverstar). Only H45 showed A acclimation to elevated [CO2], which was characterised by lower maximum Rubisco carboxylation efficiency, maximum electron transport rate and leaf N concentration. Leaf level traits responsible for plant growth, such as leaf mass per unit area (LMA), carbon (C), N content on an area basis ([N](LA)) and the C : N increased at elevated [CO2]. LMA stimulation ranged from 0% to 85% and was clearly associated with increased [N](LA). Both of these traits were positively correlated with grain yield, suggesting that differences in LMA play an important role in determining the grain yield response to elevated [CO2]. Thus increased LMA can be used as a new trait to select cultivars for a future [CO2]-rich atmosphere.
  • Authors:
    • Thomas,Amy R. C.
    • Bond,Alan J.
    • Hiscock,Kevin M.
  • Source: Global Change Biology Bioenergy
  • Volume: 5
  • Issue: 3
  • Year: 2013
  • Summary: Reduction in energy sector greenhouse gas GHG emissions is a key aim of European Commission plans to expand cultivation of bioenergy crops. Since agriculture makes up 1012% of anthropogenic GHG emissions, impacts of land-use change must be considered, which requires detailed understanding of specific changes to agroecosystems. The greenhouse gas (GHG) balance of perennials may differ significantly from the previous ecosystem. Net change in GHG emissions with land-use change for bioenergy may exceed avoided fossil fuel emissions, meaning that actual GHG mitigation benefits are variable. Carbon (C) and nitrogen (N) cycling are complex interlinked systems, and a change in land management may affect both differently at different sites, depending on other variables. Change in evapotranspiration with land-use change may also have significant environmental or water resource impacts at some locations. This article derives a multi-criteria based decision analysis approach to objectively identify the most appropriate assessment method of the environmental impacts of land-use change for perennial energy crops. Based on a literature review and conceptual model in support of this approach, the potential impacts of land-use change for perennial energy crops on GHG emissions and evapotranspiration were identified, as well as likely controlling variables. These findings were used to structure the decision problem and to outline model requirements. A process-based model representing the complete agroecosystem was identified as the best predictive tool, where adequate data are available. Nineteen models were assessed according to suitability criteria, to identify current model capability, based on the conceptual model, and explicit representation of processes at appropriate resolution. FASSET, ECOSSE, ANIMO, DNDC, DayCent, Expert-N, Ecosys, WNMM and CERES-NOE were identified as appropriate models, with factors such as crop, location and data availability dictating the final decision for a given project. A database to inform such decisions is included.
  • Authors:
    • Macdonald, B. C. T.
    • Biggs, J. S.
    • Thorburn, P. J.
    • Allen, D. E.
    • Denmead, O. T.
  • Source: Conference: Proceedings of the 35th Conference of the Australian Society of Sugar Cane Technologists held at Townsville, Queensland, Australia, 16-18 April 2013. Proceedings of the 35th Conference of the Australian Society of Sugar Cane Technologists hel
  • Year: 2013
  • Summary: NITROUS OXIDE IS a potent greenhouse gas, and emission from soils in sugarcane crops of NSW are some of the highest measured from cropping systems. Yet, not all emissions are this large and the reason for the range is unclear. The high emissions come from a site with acid sulphate soils in Australia, and chemo-denitrification in the acid subsoils have been suggested as important causes of the high emissions. However, emissions from acid sulphate soils are not always at the upper end of this range suggesting the explanation is not general. We used the APSIM model to investigate the degree to which the biological nitrous oxide-generating pathways represented in the model might (1) account for the high emissions measured in some sugarcane crops grown on acid sulphate soils, and hence (2) provide a broader understanding of the basis for the wide range of emissions associated with sugarcane. We found conditions at the site where the highest emissions were measured, particularly a combination of high soil carbon (~10%) and large applications of nitrogen fertiliser, gave simulated emissions similar to the high values measured. Sensitivity analyses showed that when soil carbon contents and/or nitrogen applications were lower, predicted emissions reduced to levels closer to those at other sites. Our results suggest that biological pathways are capable of producing the range of nitrous oxide emissions measured in sugarcane crops, and that the contribution of chemical pathways need not be great. The results have important implications for understanding both how nitrous oxide emissions from sugarcane may vary between different environments and how emissions can be mitigated; issues that are particularly important for the environmental sustainability of sugarcane production.
  • Authors:
    • Weeks, C.
    • Cordingley, N.
    • Flower, K. C.
    • Ward, P. R.
    • Micin, S. F.
  • Source: Field Crops Research
  • Volume: 132
  • Year: 2012
  • Summary: Modern conservation agriculture practices aim to maintain year-round ground cover in order to maximise soil protection from extremes of temperature and minimise erosion risk. However, in Mediterranean-style environments with hot dry summer periods, maintaining ground cover can be difficult, as these periods are generally too arid for plant growth. In this research, we investigated the use of cover crops, grown solely to increase ground cover and not harvested for grain or biomass, in a Mediterranean climate. Specifically, we examined the impact of cover crops and residue retention on evapotranspiration, both over the summer fallow period and during the winter and spring crop growth period, and on deep drainage from subsequent crops, on two contrasting soil types in south-western Australia. The impact of cover crops on weed populations and nitrogen dynamics is described in a companion paper. In contrast to previously published research, cover crops and residue retention were found to have limited impact on total evaporation during the summer and autumn period, although there were occasional short-term impacts on the rate of evaporation shortly after rainfall. There was also limited evidence of changes in evaporation during early crop growth. Drainage from crops grown after cover crops was not consistently different to drainage from crops grown after conventional crops. The inclusion of cover crops in farming systems in regions with a Mediterranean climate is unlikely to have major impacts on the water balance, but may still increase overall sustainability of the farming system.