• Authors:
    • Snapp, S. S.
    • Robertson, G. P.
    • Gelfand, I.
  • Source: Environmental Science & Technology
  • Volume: 44
  • Issue: 10
  • Year: 2010
  • Summary: The prospect of biofuel production on a large scale has focused attention on energy efficiencies associated with different agricultural systems and production goals. We used 17 years of detailed data on agricultural practices and yields to calculate an energy balance for different cropping systems under both food and fuel scenarios. We compared four grain and one forage systems in the U.S. Midwest: corn ( Zea mays) - soybean ( Glycine max) - wheat ( Triticum aestivum) rotations managed with (1) conventional tillage, (2) no till, (3) low chemical input, and (4) biologically based (organic) practices, and (5) continuous alfalfa ( Medicago sativa). We compared energy balances under two scenarios: all harvestable biomass used for food versus all harvestable biomass used for biofuel production. Among the annual grain crops, average energy costs of farming for the different systems ranged from 4.8 GJ ha -1 y -1 for the organic system to 7.1 GJ ha -1 y -1 for the conventional; the no-till system was also low at 4.9 GJ ha -1 y -1 and the low-chemical input system intermediate (5.2 GJ ha -1 y -1). For each system, the average energy output for food was always greater than that for fuel. Overall energy efficiencies ranged from output:input ratios of 10 to 16 for conventional and no-till food production and from 7 to 11 for conventional and no-till fuel production, respectively. Alfalfa for fuel production had an efficiency similar to that of no-till grain production for fuel. Our analysis points to a more energetically efficient use of cropland for food than for fuel production and large differences in efficiencies attributable to management, which suggests multiple opportunities for improvement.
  • Authors:
    • Halvorson, A. D.
    • Grosso, S. J. del
    • Alluvione, F.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: Nitrogen fertilization is essential for optimizing crop yields; however, it increases N 2O emissions. The study objective was to compare N 2O emissions resulting from application of commercially available enhanced-efficiency N fertilizers with emissions from conventional dry granular urea in irrigated cropping systems. Nitrous oxide emissions were monitored from corn ( Zea mays L.) based rotations receiving fertilizer rates of 246 kg N ha -1 when in corn, 56 kg N ha -1 when in dry bean ( Phaseolus vulgaris L.), and 157 kg N ha -1 when in barley ( Hordeum vulgare L. ssp. vulgare). Cropping systems included conventional-till continuous corn (CT-CC), no-till continuous corn (NT-CC), no-till corn-dry bean (NT-CDb), and no-till corn-barley (NT-CB). In the NT-CC and CT-CC systems, a controlled-release, polymer-coated urea (ESN) and dry granular urea were compared. In the NT-CDb and NT-CB rotations, a stabilized urea source (SuperU) was compared with urea. Nitrous oxide fluxes were measured during two growing seasons using static, vented chambers and a gas chromatograph analyzer. Cumulative growing season N 2O emissions from urea and ESN application were not different under CT-CC, but ESN reduced N 2O emissions 49% compared with urea under NT-CC. Compared with urea, SuperU reduced N 2O emissions by 27% in dry bean and 54% in corn in the NT-CDb rotation and by 19% in barley and 51% in corn in the NT-CB rotation. This work shows that the use of no-till and enhanced-efficiency N fertilizers can potentially reduce N 2O emissions from irrigated systems.
  • Authors:
    • Committee on the Impact of Biotechnology on Farm-Level Economics and Sustainability
    • National Research Council
  • Year: 2010
  • Authors:
    • Pollack, A.
    • Neuman, W.
  • Source: The New York Times
  • Volume: 4 May
  • Year: 2010
  • Summary: A 2010 article in the New York times about Round-Up resistant weeds in the United States.
  • Authors:
    • Nordhaus, W. D.
  • Source: The Economist's Voice
  • Volume: 7
  • Issue: 3
  • Year: 2010
  • Summary: A carbon tax would improve fiscal sustainability in the United States according to William Nordhaus of Yale University. There is no better fiscal instrument to employ at this time, in this country, and given the fiscal constraints the government faces.
  • Authors:
    • NRCS,USDA
  • Volume: 2010
  • Year: 2010
  • Authors:
    • Paustian, K.
    • Killian, K.
    • Williams, S.
    • Easter, M.
    • Breidt, F. J.
    • Ogle, S. M.
  • Source: Global Change Biology
  • Volume: 16
  • Issue: 2
  • Year: 2010
  • Summary: Process-based model analyses are often used to estimate changes in soil organic carbon (SOC), particularly at regional to continental scales. However, uncertainties are rarely evaluated, and so it is difficult to determine how much confidence can be placed in the results. Our objective was to quantify uncertainties across multiple scales in a processbased model analysis, and provide 95% confidence intervals for the estimates. Specifically, we used the Century ecosystem model to estimate changes in SOC stocks for US croplands during the 1990s, addressing uncertainties in model inputs, structure and scaling of results from point locations to regions and the entire country. Overall, SOC stocks increased in US croplands by 14.6 TgCyr1 from 1990 to 1995 and 17.5 TgCyr1 during 1995 to 2000, and uncertainties were 22% and 16% for the two time periods, respectively. Uncertainties were inversely related to spatial scale, with median uncertainties at the regional scale estimated at 118% and 114% during the early and latter part of 1990s, and even higher at the site scale with estimates at 739% and 674% for the time periods, respectively. This relationship appeared to be driven by the amount of the SOC stock change; changes in stocks that exceeded 200GgCyr1 represented a threshold where uncertainties were always lower than 100%. Consequently, the amount of uncertainty in estimates derived from process-based models will partly depend on the level of SOC accumulation or loss. In general, the majority of uncertainty was associated with model structure in this application, and so attaining higher levels of precision in the estimates will largely depend on improving the model algorithms and parameterization, as well as increasing the number of measurement sites used to evaluate the structural uncertainty.
  • Authors:
    • Hatfield, J. L.
    • Parkin, T. B.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 136
  • Issue: 1-2
  • Year: 2010
  • Summary: Fertilizer application in crop production agriculture has been identified as a major source of the greenhouse gas nitrous oxide. Thus, management strategies that increase fertilizer N use efficiency will reduce N2O emission. Anhydrous ammonia applied to cropland in the fall is recognized as a management practice that increases the risk of N loss from the rooting zone, however, this practice is still common in the U.S. Midwest Corn Belt. The nitrification inhibitor, nitrapyrin has been shown to decrease soil N losses during the fall and spring, and maintain fertilizer N availability to the crop. Additionally, nitrification inhibitors have shown promise in reducing soil N2O emissions. However, there have been no studies evaluating the effectiveness of nitrapyrin to reduce annual N2O emissions from land receiving fall-applied anhydrous ammonia. This study was conducted over 2 years to measure N2O emissions from corn plots with fall-applied anhydrous ammonia with and without nitrapyrin. Based on soil NO3 and NH4 analyses, we observed that nitrapyrin delayed nitrification, and in 1 year, reduced late fall/early spring N2O emission. However, annual N2O emissions were not significantly reduced. Significantly higher corn grain yields were observed in the nitrapyrin treatment in both years.
  • Authors:
    • Conant, R. T.
    • Ogle, S.
    • Paustian, K.
  • Source: Handbook of Climate Change and Agroecosystems: Impacts, Adaptation, and Mitigation
  • Year: 2010
  • Authors:
    • Payne, W. A.
  • Source: Advances in Agronomy
  • Volume: 105
  • Year: 2010
  • Summary: Sustainability of biofuels is a contentious but old topic that has reemerged with increased use of crops as feedstocks. There are vastly different land requirements for different feedstocks, and disagreement on the energy balance of their conversion to biofuel. To be sustainable, biofuel systems should (1) have favorable economics, (2) conserve natural resources, (3) preserve ecology, and (4) promote social justice. With the possible exception of sugarcane production in Brazil, it seems unlikely that ethanol production from crops will be economically viable without government support. Less is known on cellulosic feedstock economics because there are no commercial-scale plants. Natural resources that may be affected include soil, water, and air. In the United States, agricultural intensification has been associated with greater soil conservation, but this depended on retaining residue that may serve as cellulosic feedstocks. The "water footprint" of bioenergy from crops is much greater than for other forms of energy, although cellulosic feedstocks would have a smaller footprint. Most studies have found that first-generation biofuels reduce greenhouse gas emissions 20-60%, and second generation ones by 70-90%, if effects from land-use change are excluded. But land-use change may incur large carbon losses, and can affect ecological preservation, including biodiversity. Social justice is by far the most contentious sustainability issue. Expanding biofuel production was a major cause of food insecurity and political instability in 2008. There is a large debate on whether biofuels will always contribute to food insecurity, social justice, and environmental degradation in poor countries.