471. Greenhouse gas emissions from a wastewater sludge-amended soil cultivated with wheat (Triticum spp. L.) as affected by different application rates of charcoal

• Authors:
  • Luna-Guido, M.
  • Dendooven, L.
  • del Rosario Cardenas-Aquino, M.
  • Diaz-Rojas, M.
  • Aguilar-Chavez, A.
• Source: Soil Biology and Biochemistry
• Volume: 52
• Issue: September
• Year: 2012
• Summary: Applying biochar to soil is an easy way to sequester carbon in soil, while it might reduce greenhouse gas (GHG) emissions and stimulate plant growth. The effect of charcoal application (0, 1.5, 3.0 and 4.5%) on GHG emission was studied in a wastewater sludge-amended arable soil (Typic Fragiudepts) cultivated with wheat (Triticum spp. L) in a greenhouse. The application of charcoal at >= 1.5% reduced the CO2 emission rate significantly >= 37% compared to unamended soil (135.3 g CO2 ha(-1) day(-1)) in the first two weeks, while the N2O emission rate decreased 44% when 4.5% charcoal was added (0.72 g N2O ha(-1) day(-1)). The cumulative GHG emission over 45 days was 2% lower when 1.5% charcoal, 34% lower when 3.0% charcoal and 39% lower when 4.5% charcoal was applied to the sludge-amended soil cultivated with wheat. Wheat growth was inhibited in the charcoal-amended soil compared to the unamended soil, but not yields after 135 days. It was found that charcoal addition reduced the emissions of N2O and CO2, and the cumulative GHG emissions over 45 days, without altering wheat yield. (C) 2012 Elsevier Ltd. All rights reserved.

472. Greenhouse gas emission intensities and economic efficiency in crop production: A systems analysis of 95 farms

• Authors:
  • Klakegg, O.
  • Janzen, H. H.
  • Skjelvag, A. O.
  • Bonesmo, H.
  • Tveito, O. E.
• Source: Agricultural Systems
• Volume: 110
• Issue: July
• Year: 2012
• Summary: To increase food production while mitigating climate change, cropping systems in the future will need to reduce greenhouse gas emission per unit of production. We conducted an analysis of 95 arable farms in Norway to calculate farm scale emissions of greenhouse gases, expressed both as CO2 eq per unit area, and CO2 eq per kg DM produced and to describe relationships between the farms' GHG intensities and heir economic efficiencies (gross margin). The study included: (1) design of a farm scale model for net GHG emission from crop production systems; (2) establishing a consistent farm scale data set for the farms with required soil, weather, and farm operation data; (3) a stochastic simulation of the variation in the sources of GHG emission intensities, and sensitivity analysis of selected parameters and equations on GHG emission intensities; and (4) describing relationships between GHG emission intensities and gross margins on farms. Among small seed and grain crops the variation in GHG emissions per kg DM was highest in oilseed (emission intensity at the 75th percentile level was 1.9 times higher than at the 25th percentile). For barley, oats, spring wheat, and winter wheat, emissions per kg DM at the 75th percentile levels were between 1.4 and 1.6 times higher than those at the 25th percentiles. Similar trends were observed for emissions per unit land area. Invariably soil N2O emission was the largest source of GHG emissions, accounting for almost half of the emissions. The second largest source was the off farm manufacturing of inputs (similar to 25%). Except for the oilseed crop, in which soil carbon (C) change contributed least, the on farm emissions due to fuel use contributed least to the total GHG intensities (similar to 10%). The soil C change contributed most to the variability in GHG emission intensities among farms in all crops, and among the sensitivity elasticities the highest one was related to environmental impacts on soil C change. The high variation in GHG intensities evident in our study implies the potential for significant mitigation of GHG emissions. The GHG emissions per kg DM (intensity) decreased with increasing gross margin in grain and oilseed crops, suggesting that crop producers have economic incentives to reduce GHG emissions. (c) 2012 Elsevier Ltd. All rights reserved,

473. A comparison of GHG emissions from UK field crop production under selected arable systems with reference to disease control

• Authors:
  • Fitt, B. D. L.
  • Smith, P.
  • West, J. S.
  • Carlton, R. R.
• Source: European Journal of Plant Pathology
• Volume: 133
• Issue: 1
• Year: 2012
• Summary: Crop disease not only threatens global food security by reducing crop production at a time of growing demand, but also contributes to greenhouse gas (GHG) emissions by reducing efficiency of N fertiliser use and farm operations and by driving land use change. GHG emissions associated with adoption of reduced tillage, organic and integrated systems of field crop production across the UK and selected regions are compared with emissions from conventional arable farming to assess their potential for climate change mitigation. The reduced tillage system demonstrated a modest (< 20%) reduction in emissions in all cases, although in practice it may not be suitable for all soils and it is likely to cause problems with control of diseases spread on crop debris. There were substantial increases in GHG emissions associated with the organic and integrated systems at national level, principally due to soil organic carbon losses from land use change. At a regional level the integrated system shows the potential to deliver significant emission reductions. These results indicate that the conventional crop production system, coupled to reduced tillage cultivation where appropriate, is generally the best for producing high yields to minimise greenhouse gas emissions and contribute to global food security, although there may be scope for use of the integrated system on a regional basis. The control of crop disease will continue to have an essential role in both maintaining productivity and decreasing GHG emissions.

474. Consequences of field N2O emissions for the environmental sustainability of plant-based biofuels produced within an organic farming system

• Authors:
  • Schmidt, J. E.
  • Thomsen, S. T.
  • Jensen, M.
  • Heiske, S.
  • Hauggaard-Nielsen, H.
  • Carter, M. S.
  • Johansen, A.
  • Ambus, P.
• Source: GCB Bioenergy
• Volume: 4
• Issue: 4
• Year: 2012
• Summary: One way of reducing the emissions of fossil fuel-derived carbon dioxide (CO2) is to replace fossil fuels with biofuels produced from agricultural biomasses or residuals. However, cultivation of soils results in emission of other greenhouse gases (GHGs), especially nitrous oxide (N2O). Previous studies on biofuel production systems showed that emissions of N2O may counterbalance a substantial part of the global warming reduction, which is achieved by fossil fuel displacement. In this study, we related measured field emissions of N2O to the reduction in fossil fuel-derived CO2, which was obtained when agricultural biomasses were used for biofuel production. The analysis included five organically managed feedstocks (viz. dried straw of sole cropped rye, sole cropped vetch and intercropped ryevetch, as well as fresh grassclover and whole crop maize) and three scenarios for conversion of biomass into biofuel. The scenarios were (i) bioethanol, (ii) biogas and (iii) coproduction of bioethanol and biogas. In the last scenario, the biomass was first used for bioethanol fermentation and subsequently the effluent from this process was utilized for biogas production. The net GHG reduction was calculated as the avoided fossil fuel-derived CO2, where the N2O emission was subtracted. This value did not account for fossil fuel-derived CO2 emissions from farm machinery and during conversion processes that turn biomass into biofuel. The greatest net GHG reduction, corresponding to 700800 g CO2 m(-2), was obtained by biogas production or coproduction of bioethanol and biogas on either fresh grassclover or whole crop maize. In contrast, biofuel production based on lignocellulosic crop residues (i.e. rye and vetch straw) provided considerably lower net GHG reductions (=215 g CO2 m(-2)), and even negative numbers sometimes. No GHG benefit was achieved by fertilizing the maize crop because the extra crop yield, and thereby increased biofuel production, was offset by enhanced N2O emissions.

475. Greenhouse gas emissions under conservation agriculture compared to traditional cultivation of maize in the central highlands of Mexico

• Authors:
  • Vasquez-Murrieta, S.
  • Gutierrez-Miceli, F. A.
  • Montes-Molina, J.
  • Marsch, R.
  • Luna-Guido, M.
  • Verhulst, N.
  • Ramirez-Villanueva, D. A.
  • Patino-Zuniga, L.
  • Gutierrez-Oliva, V. F.
  • Dendooven, L.
  • Govaerts, B.
• Source: Science of The Total Environment
• Volume: 431
• Issue: August
• Year: 2012
• Summary: In 1991, the 'International Maize and Wheat Improvement Center' (CIMMYT) started a field experiment in the rain fed Mexican highlands to investigate conservation agriculture (CA) as a sustainable alternative for conventional maize production practices (CT). CT techniques, characterized by deep tillage, monoculture and crop residue removal, have deteriorated soil fertility and reduced yields. CA, which combines minimum tillage, crop rotations and residue retention, restores soil fertility and increases yields. Soil organic matter increases in CA compared to CT, but increases in greenhouse gas emissions (GHG) in CA might offset the gains obtained to mitigate global warming. Therefore, CO2, CH4 and N2O emissions, soil temperature, C and water content were monitored in CA and CT treatments in 2010-2011. The cumulative GHG emitted were similar for CA and CT in both years, but the C content in the 0-60 cm layer was higher in CA (117.7 Mg C ha(-1)) than in CT (69.7 Mg C ha(-1)). The net global warming potential (GWP) of CA (considering soil C sequestration, GHG emissions, fuel use, and fertilizer and seeds production) was -7729 kg CO2 ha(-1) y(-1) in 2008-2009 and -7892 kg CO2 ha(-1) y(-1) in 2010-2011, whereas that of CT was 1327 and 1156 kg CO2 ha(-1) y(-1). It was found that the contribution of CA to GWP was small compared to that of CT. (C) 2012 Elsevier B.V. All rights reserved.

476. Global warming potential of agricultural systems with contrasting tillage and residue management in the central highlands of Mexico

• Authors:
  • Marsch, R.
  • Luna-Guido, M.
  • Verhulst, N.
  • Patino-Zuniga, L.
  • Dendooven, L.
  • Govaerts, B.
• Source: Agriculture, Ecosystems & Environment
• Volume: 152
• Issue: May
• Year: 2012
• Summary: Conservation agriculture based on (1) minimal soil movement, (2) retention of rational amounts of crop residue, (3) economically viable crop rotations restores soil fertility. Conservation agriculture improves soil characteristics, but it remains to be seen how zero tillage (ZT) affected greenhouse gas emissions (GHG) and the global warming potential (GWP) compared to conventional tillage (Cr) when crop residue was kept or removed in a maize-wheat crop rotation since 1991. The soil organic C content in the 0-60 cm layer was larger in ZT (117.7 Mg C ha(-1)) compared to CT (76.8 Mg C ha(-1)) when residue was retained, but similar when it was removed. Tillage and residue management had only a small effect on GWP of the GHG emissions. However, the C sequestered in the 0-60cm was affected by tillage and crop residue management, resulting in a negative net GWP for ZT with crop residue retention (-6.277 Mg CO2 ha(-1) y(-1)) whereas in the other management practices it ranged from 1.288 to 1.885 Mg CO2 ha(-1) y(-1). It was found that cultivation technique had little effect on the GWP of the GHG, but had a large effect on C sequestered in the 0-60cm layer and the net GWP. (C) 2012 Elsevier B.V. All rights reserved.

477. Land-use change to bioenergy production in Europe: implications for the greenhouse gas balance and soil carbon

• Authors:
  • Zegada-Lizarazu, W.
  • Walter, K.
  • Valentine, J.
  • Djomo, S. Njakou
  • Monti, A.
  • Mander, U.
  • Lanigan, G. J.
  • Jones, M. B.
  • Hyvonen, N.
  • Freibauer, A.
  • Flessa, H.
  • Drewer, J.
  • Carter, M. S.
  • Skiba, U.
  • Hastings, A.
  • Osborne, B.
  • Don, A.
  • Zenone, T.
• Source: GCB Bioenergy
• Volume: 4
• Issue: 4
• Year: 2012
• Summary: Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO2, N2O and CH4 during crop production may reduce or completely counterbalance CO2 savings of the substituted fossil fuels. These greenhouse gases (GHGs) need to be included into the carbon footprint calculation of different bioenergy crops under a range of soil conditions and management practices. This review compiles existing knowledge on agronomic and environmental constraints and GHG balances of the major European bioenergy crops, although it focuses on dedicated perennial crops such as Miscanthus and short rotation coppice species. Such second-generation crops account for only 3% of the current European bioenergy production, but field data suggest they emit 40% to >99% less N2O than conventional annual crops. This is a result of lower fertilizer requirements as well as a higher N-use efficiency, due to effective N-recycling. Perennial energy crops have the potential to sequester additional carbon in soil biomass if established on former cropland (0.44 Mg soil C ha(-1) yr(-1) for poplar and willow and 0.66 Mg soil C ha(-1) yr(-1) for Miscanthus). However, there was no positive or even negative effects on the C balance if energy crops are established on former grassland. Increased bioenergy production may also result in direct and indirect land-use changes with potential high C losses when native vegetation is converted to annual crops. Although dedicated perennial energy crops have a high potential to improve the GHG balance of bioenergy production, several agronomic and economic constraints still have to be overcome.

478. How do soil emissions of N2O, CH4 and CO2 from perennial bioenergy crops differ from arable annual crops?

• Authors:
  • Skiba, U.
  • Baggs, E. M.
  • Lloyd, C. R.
  • Finch, J. W.
  • Drewer, J.
• Source: GCB Bioenergy
• Volume: 4
• Issue: 4
• Year: 2012
• Summary: It is important to demonstrate that replacing fossil fuel with bioenergy crops can reduce the national greenhouse gas (GHG) footprint. We compared field emissions of nitrous oxide (N2O), methane (CH4) and soil respiration rates from the C-4 grass Miscanthus x giganteus and willow (salix) with emissions from annual arable crops grown for food production. The study was carried out in NE England on adjacent fields of willow, Miscanthus, wheat (Triticum aetivum) and oilseed rape (Brassica napus). N2O, CH4 fluxes and soil respiration rates were measured monthly using static chambers from June 2008 to November 2010. Net ecosystem exchange (NEE) of carbon dioxide (CO2) was measured by eddy covariance on Miscanthus from May 2008 and on willow from October 2009 until November 2010. The N2O fluxes were significantly smaller from the bioenergy crops than that of the annual crops. Average fluxes were 8 and 32 mu g m(-2) h(-1) N2O-N from wheat and oilseed rape, and 4 and 0.2 mu g m(-2) h(-1) N2O-N from Miscanthus and willow, respectively. Soil CH4 fluxes were negligible for all crops and soil respiration rates were similar for all crops. NEE of CO2 was larger for Miscanthus (-770 g C m(-2) h(-1)) than willow (-602 g C m(-2) h(-1)) in the growing season of 2010. N2O emissions from Miscanthus and willow were lower than for the wheat and oilseed rape which is most likely a result of regular fertilizer application and tillage in the annual arable cropping systems. Application of N-15-labelled fertilizer to Miscanthus and oil seed rape resulted in a fertilizer-induced increase in N2O emission in both crops. Denitrification rates (N2O + N-2) were similar for soil under Miscanthus and oilseed rape. Thus, perennial bioenergy crops only emit less GHGs than annual crops when they receive no or very low rates of N fertilizer.

479. Life cycle assessment modelling of complex agricultural systems with multiple food and fibre co-products

• Authors:
  • Grant, T.
  • Carre, A.
  • Eady, S.
• Source: Journal of Cleaner Production
• Volume: 28
• Issue: June
• Year: 2012
• Summary: Most agricultural products are produced on farms where there is a mix of activities, resulting in a range of co-products. This raises the issue of how best to model these complex production systems for Life Cycle Assessment, especially where there are benefits imparted by one activity in the mixed farming system to another. On the mixed farm studied, there were significant two-way reference flows (representing 288 t CO2-e/year or 10% of the total farm emissions) between activities producing distinct products (wool, meat, grain) and these were modelled using system expansion. Cropping and sheep activities were modelled as separate sub-processes in the farming system, with unique inputs and outputs identified for each. Co-production from the sheep activity was modelling using allocation, comparing biophysical and economic relationships. Using an economic allocation resulted in different estimates of global warming impact for sheep co-products, with figures varying by 7-52%. When compared to biophysical allocation, economic allocation shifted the environmental burden to the higher value co-products and away from the high resource use products. Using economic allocation, for every kilogram of wool produced there was an estimated 28.7 kg of CO2-e emitted. Amongst the live animal products, the stud rams had the highest estimated carbon footprint (719 kg CO2-e/ram). Amongst the crops, estimates of emissions for the cereal grains averaged 202 kg CO2-e/tonne grain, canola 222 kg CO2-e/tonne and lupins 510 kg CO2-e/tonne, when modelled to include the benefits of the mixed farming system. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

480. Evaluating soil organic carbon sequestration potential in the Cotton Belt with the soil conditioning index

• Authors:
  • Hubbs, M. D.
  • Franzluebbers, A. J.
  • Norfleet, M. L.
• Source: Journal of Soil and Water Conservation
• Volume: 67
• Issue: 5
• Year: 2012
• Summary: Simulation models that are sensitive to management, edaphic factors, and climate could provide insights into how land owners and producers might be able to sequester soil organic carbon (C) and engage in emerging carbon markets. In this study, the soil conditioning index (SCI) embedded in the Revised Universal Soil Loss Equation (RUSLE2) model was used to predict (1) potential soil organic C sequestration under conventional and conservation management of a diversity of cotton cropping systems throughout the Cotton Belt and (2) relative influences of soil texture, slope, climatic conditions, and management on potential soil organic C sequestration. Across 10 regions of the Cotton Belt, SCI scores ranked in the following order: perennial pasture > no-till cropping systems > conventional tillage cotton. Variations in significance of SCI scores occurred among 5 different no-till cropping systems within regions of the Cotton Belt. For example, 7 of the 10 regions had significantly (p <= 0.05) greater SCI scores (linked to greater soil organic C sequestration) when monoculture cotton was grown with winter cover crop than without.Variation in SCI was dominated by management (46%) and slope (24%) and very little affected by climate (7%) and soil texture (1%). Increasingly wetter climatic conditions (as expressed by increasing precipitation to potential evapotranspiration) had a negative influence on SCI scores for all management systems and land slopes evaluated, but particularly for moldboard-plowed cotton on sloping land, With a linear relationship between SCI and soil organic C sequestration, predicted soil organic C sequestration averaged -0.31 +/- 0.19 Mg C ha(-1) y(--1) (-280 +/- 170 lb ac(-1) yr(-1)) under conventionally tilled cotton, 0.12 +/- 0.06 Mg C ha(-1) y(-1) (103 +/- 52 lb ac(-1) yr(-1)) under various no-till crop rotations, and 0.26 +/- 0.02 Mg C ha(-1) y(-1) (231 +/- 20 lb ac(-1) yr(-1)) under perennial pasture. Cotton production with conventional tillage could only be expected to maintain soil organic C under a best-case scenario and would lose substantial soil organic C under most other scenarios. Simulations showed the strong, positive influence that conservation agricultural management has to sequester soil organic C, irrespective of climate, slope, and texture.