• Authors:
    • Sauer, T.
    • Soolaneyakanahally, R.
    • de Gooijer, H.
    • Bentrup, G.
    • Schoeneberger, M.
    • Brendle, J.
    • Zhou, X.
    • Current, D.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 5
  • Year: 2012
  • Authors:
    • Joergensen, R. G.
    • Schweinsberg-Mickan, M. S. Z.
    • Mueller, T.
  • Source: Journal of Plant Nutrition and Soil Science
  • Volume: 175
  • Issue: 5
  • Year: 2012
  • Summary: A greenhouse rhizobox experiment was carried out to investigate the fate and turnover of 13C- and 15N-labeled rhizodeposits within a rhizosphere gradient from 08?mm distance to the roots of wheat. Rhizosphere soil layers from 01, 12, 23, 34, 46, and 68?mm distance to separated roots were investigated in an incubation experiment (42 d, 15 degrees C) for changes in total C and N and that derived from rhizodeposition in total soil, in soil microbial biomass, and in the 0.05 M K2SO4extractable soil fraction. CO2-C respiration in total and that derived from rhizodeposition were measured from the incubated rhizosphere soil samples. Rhizodeposition C was detected in rhizosphere soil up to 46?mm distance from the separated roots. Rhizodeposition N was only detected in the rhizosphere soils up to 34?mm distance from the roots. Microbial biomass C and N was increased with increasing proximity to the separated roots. Beside 13C and 15N derived from rhizodeposits, unlabeled soil C and N (native SOM) were incorporated into the growing microbial biomass towards the roots, indicating a distinct acceleration of soil organic matter (SOM) decomposition and N immobilization into the growing microbial biomass, even under the competition of plant growth. During the soil incubation, microbial biomass C and N decreased in all samples. Any decrease in microbial biomass C and N in the incubated rhizosphere soil layers is attributed mainly to a decrease of unlabeled (native) C and N, whereas the main portion of previously incorporated rhizodeposition C and N during the plant growth period remained immobilized in the microbial biomass during the incubation. Mineralization of native SOM C and N was enhanced within the entire investigated rhizosphere gradient. The results indicate complex interactions between substrate input derived from rhizodeposition, microbial growth, and accelerated C and N turnover, including the decomposition of native SOM (i.e., rhizosphere priming effects) at a high spatial resolution from the roots.
  • Authors:
    • McKone, T. E.
    • Horvath, A.
    • Santero, N. J.
    • Masanet, E.
    • Lobscheid, A. B.
    • Strogen, B.
    • Mishra, U.
    • Nazaroff, W. W.
    • Scown, C. D.
  • Source: Environmental Research Letters
  • Volume: 7
  • Issue: 1
  • Year: 2012
  • Summary: The Energy Independence and Security Act of 2007 set an annual US national production goal of 39.7 billion 1 of cellulosic ethanol by 2020. This paper explores the possibility of meeting that target by growing and processing Miscanthus x giganteus. We define and assess six production scenarios in which active cropland and/or Conservation Reserve Program land are used to grow to Miscanthus. The crop and biorefinery locations are chosen with consideration of economic, land-use, water management and greenhouse gas (GHG) emissions reduction objectives. Using lifecycle assessment, the net GHG footprint of each scenario is evaluated, providing insight into the climate costs and benefits associated with each scenario's objectives. Assuming that indirect land-use change is successfully minimized or mitigated, the results suggest two major drivers for overall GHG impact of cellulosic ethanol from Miscanthus: (a) net soil carbon sequestration or emissions during Miscanthus cultivation and (b) GHG offset credits for electricity exported by biorefineries to the grid. Without these factors, the GHG intensity of bioethanol from Miscanthus is calculated to be 11-13 g CO2-equivalent per MJ of fuel, which is 80-90% lower than gasoline. Including soil carbon sequestration and the power-offset credit results in net GHG sequestration up to 26 g CO2-equivalent per MJ of fuel.
  • Authors:
    • Bakken, L.
    • Budai, A.
    • Chen, R.
    • Senbayram, M.
    • Dittert, K.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 147
  • Issue: January
  • Year: 2012
  • Summary: Amending agricultural soils with organic residues is frequently recommended to improve soil fertility and to sequester carbon for counteracting global warming. However, such amendments will enhance microbial respiration, hence denitrification. Therefore, the assessment of effects on global warming must take N2O emission and the N2O/(N2O + N-2) product ratio of denitrification into account. There are some indications that the product ratio of denitrification is positively correlated with the ratio of available NO3- and available organic C in soils, but more research is needed to unravel quantitative relationships in well defined experiments. We conducted two laboratory incubation experiments, with the objective (i) to test the impact of the application of various N containing organic substrates including biogas residue on the denitrification rate and on N2O emission, and (ii) to investigate the effect of various NO3- concentrations on the denitrification rate and the N2O/(N2O + N-2) product ratio under standardized anoxic conditions in soils collected from long-term organic or inorganic fertilizer plots. In experiment 1, we found that biogas residue was more recalcitrant than maize straw, despite a high concentration of soluble organic C. High respiration (treatments with maize straw and sucrose) resulted in a transient peak in N2O emission, declining rapidly towards zero as nitrate concentrations reached less than 20 mg NO3--N kg(-1) dry soil. Application of biogas residue had a more moderate effect on soil respiration and denitrification, and resulted in a more long lasting peak in N2O emission. The results were interpreted as a result of a gradual increase in the relative activity of N2O reductase (thus lowering of the N2O/(N2O + N-2) product ratio of denitrification) throughout the incubation, most likely controlled by concentration of available NO3- in soil. In the second experiment, we found low N2O/(N2O N-2) product ratios for the treatment where NO3- concentrations were = 10 mM NO3-, and the ratios were remarkably independent of the soil's fertilizer history. We conclude that (i) in N-fertilized agricultural soils, application of organic matter with high contents of labile C may trigger denitrification-derived N2O emission whereas (ii) in soils with low NO3- contents such application may substantially lower the N2O/(N2O + N-2) product ratio and hence N2O emission. (C) 2011 Elsevier B.V. All rights reserved.
  • Authors:
    • Lence, S.
    • Livingston, M.
    • Greene, C.
    • Chase, C.
    • Delate, K.
    • Singerman, A.
    • Hart, C.
  • Source: Renewable Agriculture and Food Systems
  • Volume: 27
  • Issue: 4
  • Year: 2012
  • Summary: Emphasis on reducing emissions from the greenhouse gases (GHG), carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) has increased in recent years in the USA, primarily for industry, transportation, energy and agricultural sectors. In this study, we utilized on-farm data collected by the USDA-National Agricultural Statistics Service (NASS) Agricultural Resource Management Survey (ARMS), secured under an agreement with the USDA-Economic Research Service (ERS) to analyze the profitability of organic and conventional soybean production, based on changes that 'green payments' in a cap-and-trade system would introduce in agricultural markets in the USA. In particular, the analysis focused on establishing whether organic producers would be better positioned to sequester carbon (C) and reap the benefits of the C-offset scheme compared to conventional producers, given the differences in costs, management practices and environmental benefits between organic and conventional production methods. We estimated several changes in profitability of soybean producers according to management practices, incentives for the generation of offset credits, and increase in energy input prices that a potential cap-and-trade system may introduce in future agricultural markets in the USA. Survey data suggested that even with lower yields, conventional producers could profit from converting to organic agriculture, given organic price premiums. In addition, taking into consideration both direct and indirect costs, average cost for conventional-till (CT) organic soybean production was approximately 9% lower than no-till (NT) conventional production. With a C market and payments for soil C sequestration through potential Clean Energy legislation, additional profit could be accrued by organic producers, because organic production would have 28% greater ton CO2 eq. acre(-1) yr(-1) sequestration than conventional NT. Thus, the environmental benefits from GHG reduction could incentivize increased conversion from conventional to organic production across the USA.
  • Authors:
    • Klakegg, O.
    • Arnoldussen, A. H.
    • Skjelvag, A. O.
    • Tveito, O. E.
  • Source: Acta Agriculturae Scandinavica, Section A — Animal Science
  • Volume: 62
  • Issue: 4
  • Year: 2012
  • Summary: Models for an holistic analysis of a farm's greenhouse gas (GHG) emissions are available, e.g. HolosNor. They require access to a farm's management data and its soil and climatic conditions. The objective of this investigation was to demonstrate how available soil and climatic data can be used to provide the required inputs of a farm's natural resource base. Soil type recordings from six municipalities representing main agroclimatic zones of Norway were used. By means of a soil moisture model a combined index of soil moisture and temperature was estimated for use in a carbon balance model, also taking crop species into account. Water filled pore space (Wfps) to saturation and soil temperature were estimated for calculation of emission of nitrous oxide. Input variables for calculation of GHG emissions varied considerably among municipalities and among farms therein.
  • Authors:
    • Huggins, D.
    • Nelson, R.
    • Kemanian, A.
    • Higgins, S.
    • Stoeckle, C.
    • Marcos, J.
    • Collins, H.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 5
  • Year: 2012
  • Summary: Conservation tillage is an agricultural strategy to mitigate atmospheric greenhouse gas (GHG) emissions. In eastern Washington, we evaluated the long-term effects of conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) on soil organic carbon (SOC) storage and nitrous oxide (N2O) emissions at three dryland and one irrigated location using the cropping systems simulation model CropSyst. Conversion of CT to NT produced the largest relative increase in SOC storage (Delta SOC, average yearly change relative to CT) in the top 30 cm (11.8 in) of soil where Delta SOC ranged from 0.29 to 0.53 Mg CO(2)e ha(-1) y(-1) (CO(2)e is carbon dioxide [CO2] equivalent of SOC; 0.13 to 0.24 tn CO(2)e ac(-1) yr(-1)).The Delta SOC were less with lower annual precipitation, greater fallow frequency, and when changing from CT to RT. Overall, Delta SOC decreased from the first to the third decade after conversion from CT to NT or RT. Simulations of Delta SOC for the conversion of CT to NT based on a 0 to 15 cm (0 to 5.9 in) soil depth were greater than the Delta SOC based on a 0 to 30 cm depth, primarily due to differences among tillage regimes in the depth-distribution of carbon (C) inputs and the resultant SOC distribution with depth. Soil erosion rates under CT in the study region are high, posing deleterious effects on soil quality, productivity, and aquatic systems. However, an analysis that includes deposition, burial, and sedimentation on terrestrial and aquatic systems of eroded SOC indicates that the substantial erosion reduction obtained with RT and NT may result only in minor additional SOC oxidation as compared to CT Simulated N2O emissions, expressed as CO2 equivalent, were not very different under CT, RT, and NT However, N2O emissions were sufficiently high to offset gains in SOC from the conversion of CT to RT or NT.Thus, reducing tillage intensity can result in net C storage, but mitigation of GHG is limited unless it is coupled with nitrogen (N) fertilizer management to also reduce N2O emission.
  • Authors:
    • Hellweg, S.
    • Pfister, S.
    • Juraske, R.
    • Stoessel, F.
  • Source: Environmental Science & Technology
  • Volume: 46
  • Issue: 6
  • Year: 2012
  • Summary: Food production and consumption is known to have significant environmental impacts. In the present work, the life cycle assessment methodology is used for the environmental assessment of an assortment of 34 fruits and vegetables of a large Swiss retailer, with the aim of providing environmental decision-support to the retailer and establishing life cycle inventories (LCI) also applicable to other case studies. The LCI includes, among others, seedling production, farm machinery use, fuels for the heating of greenhouses, irrigation, fertilizers, pesticides, storage and transport to and within Switzerland. The results show that the largest reduction of environmental impacts can be achieved by consuming seasonal fruits and vegetables, followed by reduction of transport by airplane. Sourcing fruits and vegetables locally is only a good strategy to reduce the carbon footprint if no greenhouse heating with fossil fuels is involved. The impact of water consumption depends on the location of agricultural production. For some crops a trade-off between the carbon footprint and the induced water stress is observed. The results were used by the retailer to support the purchasing decisions and improve the supply chain management.
  • Authors:
    • Walker, M. B.
    • Faber, A.
    • Syp, A.
  • Source: Journal of Food, Agriculture & Environment
  • Volume: 10
  • Issue: 3-4
  • Year: 2012
  • Summary: In this paper, simulations with a Denitrification -Decomposition (DNDC) model were used to evaluate the impact of different management options on carbon (C) sequestration and emission of greenhouse gases: methane (CH 4) and nitrous oxide (N2O). Two cropping systems were analyzed. The first included potato, winter wheat, spring barley and forage maize (P-W-B-M). The second included potato, winter wheat, spring barley with clover and grass mixture (P-W-B-C). In both cropping systems, different farmyard manure (FYM) rates were applied. The application of additional nitrogen (N) using FYM increased the C sequestration, as well as N2O emissions and had a little effect on CH 4 uptake. An estimate into the average annual increases in N2O emissions, which were converted into carbon dioxide (CO2) equivalent emissions with 100-year global warming potential (GWP) multipliers, were offset by 56-144% of the C sequestration, depending on the management option. After 16 years of the experiment, the accumulation of C and N per hectare increased in the soil organic matter (SOM) pool. In P-W-B-M rotation, with manure applied at 325 kg N ha(-1), the accumulation of C increased to 5,760 and N 585 kg ha(-1), respectively. In P-W-B-C rotation, where a higher rate of manure was applied, the increase of C was at 10,796 and N 740 kg ha(-1). The highest influence in the rise of C and N accumulation was in humates. The high value of C sequestration in soil outweighs the emissions of N2O. In P-W-B-M rotations, the rate of applied FYM switched its average annual net GWP balance from net losses to a net sink. In P-W-B-C rotations, the applied FYM increased the annual rate of GHG emissions by 3%. The average annual N2O emissions increased by 44% under P-W-B-C rotation and by 142% under P-W-B-M rotations. Increases in the soil organic carbon (SOC) were by 234% and 408%, respectively, for P-W-B-C and P-W-B-M rotations. Our study showed that usage of FYM should be managed correctly, because applications at high rates have a negative impact on environment.
  • Authors:
    • Astrup, T.
    • Wenzel, H.
    • Hamelin, L.
    • Tonini, D.
  • Source: Environmental Science & Technology
  • Volume: 46
  • Issue: 24
  • Year: 2012
  • Summary: In the endeavor of optimizing the sustainability of bioenergy production in Denmark, this consequential life cycle assessment (LCA) evaluated the environmental impacts associated with the production of heat and electricity from one hectare of Danish arable land cultivated with three perennial crops: ryegrass (Lolium perenne), willow (Salix viminalis) and Miscanthus giganteus. For each, four conversion pathways were assessed against a fossil fuel reference: (I) anaerobic co-digestion with manure, (II) gasification, (III) combustion in small-to-medium scale biomass combined heat and power (CHP) plants and IV) co-firing in large scale coal-fired CHP plants. Soil carbon changes, direct and indirect land use changes as well as uncertainty analysis (sensitivity, MonteCarlo) were included in the LCA. Results showed that global warming was the bottleneck impact, where only two scenarios, namely willow and Miscanthus co-firing, allowed for an improvement as compared with the reference (-82 and -45 t CO2-eq. ha(-1), respectively). The indirect land use changes impact was quantified as 310 + 170 t CO2-eq. ha(-1), representing a paramount average of 41% of the induced greenhouse gas emissions. The uncertainty analysis confirmed the results robustness and highlighted the indirect land use changes uncertainty as the only uncertainty that can significantly change the outcome of the LCA results.