• Authors:
    • Hoben, J. P.
    • Gehl, R. J.
    • Grace, P. R.
    • Robertson, G. P.
    • Millar, N.
  • Source: Mitigation and Adaptation Strategies for Global Change
  • Volume: 15
  • Issue: 2
  • Year: 2010
  • Summary: Nitrous oxide (N2O) is a major greenhouse gas (GHG) product of intensive agriculture. Fertilizer nitrogen (N) rate is the best single predictor of N2O emissions in row-crop agriculture in the US Midwest. We use this relationship to propose a transparent, scientifically robust protocol that can be utilized by developers of agricultural offset projects for generating fungible GHG emission reduction credits for the emerging US carbon cap and trade market. By coupling predicted N2O flux with the recently developed maximum return to N (MRTN) approach for determining economically profitable N input rates for optimized crop yield, we provide the basis for incentivizing N2O reductions without affecting yields. The protocol, if widely adopted, could reduce N2O from fertilized row-crop agriculture by more than 50%. Although other management and environmental factors can influence N2O emissions, fertilizer N rate can be viewed as a single unambiguous proxy--a transparent, tangible, and readily manageable commodity. Our protocol addresses baseline establishment, additionality, permanence, variability, and leakage, and provides for producers and other stakeholders the economic and environmental incentives necessary for adoption of agricultural N2O reduction offset projects.
  • Authors:
    • Monke, J.
  • Source: CRS Report for Congress
  • Year: 2010
  • Authors:
    • Schoeneberger, M. M.
    • Paustian, K.
    • Fry, R.
    • Franzluebbers, A. J.
    • Dijkstra, F.
    • Derner, J. D.
    • Del Grosso, S. J.
    • Allen, L. H. Jr.
    • Follett, R. F.
    • Morgan, J. A.
  • Source: Journal of Soil and Water Conservation
  • Volume: 65
  • Issue: 1
  • Year: 2010
  • Summary: from conclusion: "In agriculture, C sequestration research has tended to focus primarily on productive cropping systems. Too few experiments have specifically addressed best management practices for improving soil C storage, and fewer yet evaluate practices to reduce emissions of non-CO2 trace gases. Research needs to be expanded to less well-defined components of US agriculture. Despite occupying 37% of total US land area, relatively little research has evaluated how different management practices may affect C sequestration in US rangelands and pasture lands. Even less is known about the management potential for mitigating GHG emissions in the US horticulture industry and for turfgrass. Organic soils and wetlands present especially complex management challenges since they involve significant emissions of more than one GHG, and practices that reduce emissions of one GHG may stimulate another. Agroforestry contributions to GHG mitigation have not been considered in national inventories. Addressing these research needs, including the challenges presented by biofuels development and climate change feedbacks on agricultural GHG emissions, will be critical for giving US agriculture the necessary tools to mitigate climate change. Continued progress on scaling and monitoring methodologies will be essential to implement regional/national analyses and assessments that climate change policies and protocols will demand."
  • Authors:
    • Ellsworth, T. R.
    • Khan, S. A.
    • Mulvaney, R. L.
  • Source: Journal of Environmental Quality
  • Volume: 39
  • Issue: 2
  • Year: 2010
  • Summary: last paragraph: "In the modern era of intensified agriculture, soils are generally managed as a commodity to maximize short-term economic gain. Unfortunately, this concept entirely ignores the consequences for a vast array of biotic and abiotic soil processes that affect air and water quality and most important, the soil itself. After five decades of agrocentric management, the world's arable soils have been degraded and cereal production is increasingly exceeded by grain demand for a burgeoning human population. Should not an issue with global economic, political, and environmental ramifications be taken seriously?"
  • Authors:
    • Baker, J. S.
    • Murray, B. C.
  • Source: Greenhouse Gas Measurement and Management
  • Volume: 1
  • Issue: 1
  • Year: 2010
  • Summary: US legislators have recently proposed output-based emissions intensity metrics as an approach to credit greenhouse gas (GHG) offsets from agriculture and other uncapped sectors. This article explains the features and rationale of the output-based offset (OBO) approach, outlines a candidate accounting methodology, discusses the potential advantages and limitations of such an approach relative to the area-based offset (ABO) approach that is standard practice in some settings, and introduces possible policy implications. By incentivizing improvements in agricultural efficiency, the OBO approach strives to achieve the dual goals of food security and climate change mitigation. It expands the toolkit for achieving reductions in agricultural emissions, rewards technological advancement in both emission reductions and yields, and offers promise for addressing the problem of accounting for leakage. But because it is based on improvements in GHG efficiency in agriculture rather than on absolute reductions, emissions and climate risks could continue to rise while credits are being issued. An OBO approach might work best as a transitional strategy to address emissions from sectors or countries likely to remain outside a strict regulatory cap. Because it is the total atmospheric concentration of GHGs that creates the environmental threat of climate change, policies should ultimately focus not on the intensity of emissions but rather on their absolute levels.
  • Authors:
    • Fargione, J.
    • Wiens, J.
    • Kline, K. L.
    • Dale, V. H.
  • Source: Biofuels and Sustainability Reports
  • Year: 2010
  • Summary: from conclusions: "The implications of biofuel production and feedstock choices for land use and biodiversity are important, ranging from effects on individual fields to watersheds (which can be as big as the 48% of the US that drains into the Gulf of Mexico) to potentially the entire world. .... There are ways in which biofuels can be developed to enhance their coexistence with biodiversity. Landscape heterogeneity can be enhanced by interspersion of land uses, which is easier around production facilities with smaller feedstock demands. The development of biofuel feedstocks that yield high net energy returns with minimal carbon debts, or that do not require land for production, should be encouraged. Competing land uses (including food, fiber, and biofuel production, biodiversity protection, and urban and suburban expansion) should be subjected to comprehensive analysis and planning, so that incentives can be directed where they will do the most good. Finally, the opportunity to design bioenergy feedstock systems to optimize socioeconomic and ecologic benefits must build from the growing scientific understanding of effects of bioenergy choices at different scales, quantitative metrics, and ways to deal with environmental tradeoffs.
  • Authors:
    • Six, J.
    • Lee, J.
    • Temple, S. R.
    • Rolston, D. E.
    • Mitchell, J.
    • Kaffka, S. R.
    • Wolf, A.
    • De Gryze, S.
  • Source: Ecological Applications
  • Volume: 20
  • Issue: 7
  • Year: 2010
  • Summary: Despite the importance of agriculture in California's Central Valley, the potential of alternative management practices to reduce soil greenhouse gas (GHG) emissions has been poorly studied in California. This study aims at (1) calibrating and validating DAYCENT, an ecosystem model, for conventional and alternative cropping systems in California's Central Valley, (2) estimating CO2, N2O and CH4 soil fluxes from these systems, and (3) quantifying the uncertainty around model predictions induced by variability in the input data. The alternative practices considered were cover cropping, organic practices, and conservation tillage. These practices were compared with conventional agricultural management. The crops considered were beans, corn, cotton, safflower, sunflower, tomato, and wheat. Four field sites for which at least five years of measured data were available, were used to calibrate and validate the DAYCENT model. The model was able to predict 86% to 94% of the measured variation in crop yields and 69% to 87% of the measured variation in soil organic carbon (SOC) contents. A Monte-Carlo analysis showed that the predicted variability of SOC contents, crop yields and N2O fluxes was generally smaller than the measured variability of these parameters, in particular for N2O fluxes. Conservation tillage had the smallest potential to reduce GHG emissions among the alternative practices evaluated, with a significant reduction of the net soil GHG fluxes in two of the three sites of 336 ± 47 (mean ± standard error) and 550 ± 123 kg CO2-eq ha-1 yr-1. Cover cropping had a larger potential, with net soil GHG flux reductions of 752 ± 10, 1072 ± 272 and 2201 ± 82 kg CO2-eq ha-1 yr-1. Organic practices had the greatest potential for soil GHG flux reduction, with 4577 ± 272 kg CO2-eq ha-1 yr-1. Annual differences in weather or management conditions contributed more to the variance in annual GHG emissions than soil variability did. We concluded that the DAYCENT model was successful at predicting GHG emissions of different alternative management systems in California, but that a sound error analysis must accompany the predictions to understand the risks and potentials of GHG mitigation through adoption of alternative practices.
  • Authors:
    • Del Grosso, S. J.
  • Source: Nature
  • Volume: 464
  • Issue: 7290
  • Year: 2010
  • Summary: Most emissions of nitrous oxide from semi-arid, temperate grasslands usually occur during the spring thaw. The effects that grazing has on plant litter and snow cover dramatically reduce these seasonal emissions.
  • Authors:
    • Breidt, F. J.
    • Parton, W. J.
    • Ogle, S. M.
    • Del Grosso, S. J.
  • Source: Global Biogeochemical Cycles
  • Volume: 24
  • Year: 2010
  • Summary: [1] A Monte Carlo analysis was combined with an empirically based approach to quantify uncertainties in soil nitrous oxide (N2O) emissions from U.S. croplands estimated with the DAYCENT simulation model. Only a subset of croplands was simulated in the Monte Carlo analysis, which was used to infer uncertainties across the larger spatiotemporal domain. Specifically, one simulation representing dominant weather, soil type, and N inputs was performed for each major commodity crop in the 3000 counties occurring within the conterminous United States. We randomly selected 300 counties for the Monte Carlo analysis and randomly drew model inputs from probability distribution functions (100 iterations). A structural uncertainty estimator was developed by deriving a statistical equation from a comparison of DAYCENT simulated N2O emissions with measured emissions from experiments in North America. We estimated soil N2O emission of 201 Gg N from major commodity crops in 2007, with a 95% confidence interval (CI) of 133-304 Gg N. This implies a relative CI of 34% below and 51% above the estimate at the national scale, but the CIs tended to be larger at the regional level, particularly in regions with low emissions. Spatial variability in emissions was driven primarily by differences in N inputs from fertilizer and manure, while temporal variability was driven more by N mineralization rates, which are correlated with weather patterns in DAYCENT. A higher portion of total uncertainty was due to model structure compared to model inputs, suggesting that improvements in model algorithms and parameterization are needed to produce results with higher precision and accuracy.
  • Authors:
    • Ogle, S.
    • Del Grosso, S.
    • Delgado, J.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 86
  • Issue: 3
  • Year: 2010
  • Summary: It is difficult to quantify nitrogen (N) losses from agricultural systems; however, we can use 15N isotopic techniques to conduct site-specific studies to increase our knowledge about N management and fate. Our manuscript analyzes two reviews of selected 15N isotopic studies conducted to monitor N fate. The mechanistic foci of these studies include crop residue exchange and N fate in farming systems. Analysis of the data presented in these studies supports the claim that the average N losses are greater from inorganic N fertilizer inputs than organic crop residue N inputs. Additionally we conducted unique DAYCENT simulations of the effects of crop residue on nitrous oxide (N2O-N) emissions and nitrate (NO3-N) leaching. The simulation evaluations support the crop residue 15N exchange studies and show lower leaching and N2O-N emissions from crop residue sources when compared to N fertilizer. The 15N data suggest that the N in the crop residue pool must be recycled, and that this is a slower and more protected pool when compared to the readily available fertilizer. The results suggest that the Intergovernmental Panel on Climate Change (IPCC) methodology should be reevaluated to determine whether the direct and indirect N2O-N emission coefficients need to be lowered to reflect fewer N2O-N emissions from high C/N crop residue N inputs. The data suggest that accounting for nutrient cycling has implications for public policy associated with the United Nations Framework Convention on Climate Change (UNFCCC) and mitigation of N2O-N emissions from agricultural soils. Additional crop residue exchange studies, field N2O-N and NO3-N leaching and support model evaluations are needed across different worldwide agroecosystems.