• Authors:
    • Grace, P. R.
    • Robertson, G. P.
    • Millar, N.
    • Colunga-Garcia, M.
    • Basso, B.
    • Gage, S. H.
    • Hoben, J. P.
  • Source: Agricultural Systems
  • Volume: 104
  • Issue: 3
  • Year: 2010
  • Summary: Agricultural soils emit about 50% of the global flux of N2O attributable to human influence, mostly in response to nitrogen fertilizer use. Recent evidence that the relationship between N2O fluxes and N-fertilizer additions to cereal maize are non-linear provides an opportunity to estimate regional N2O fluxes based on estimates of N application rates rather than as a simple percentage of N inputs as used by the Intergovernmental Panel on Climate Change (IPCC). We combined a simple empirical model of N2O production with the SOCRATES soil carbon dynamics model to estimate N2O and other sources of Global Warming Potential (GWP) from cereal maize across 19,000 cropland polygons in the North Central Region (NCR) of the US over the period 1964-2005. Results indicate that the loading of greenhouse gases to the atmosphere from cereal maize production in the NCR was 1.7 Gt CO2e, with an average 268 t CO2e produced per tonne of grain. From 1970 until 2005, GHG emissions per unit product declined on average by 2.8 t CO2e ha-1 annum-1, coinciding with a stabilisation in N application rate and consistent increases in grain yield from the mid-1970s. Nitrous oxide production from N fertilizer inputs represented 59% of these emissions, soil C decline (0-30 cm) represented 11% of total emissions, with the remaining 30% (517 Mt) from the combustion of fuel associated with farm operations. Of the 126 Mt of N fertilizer applied to cereal maize from 1964 to 2005, we estimate that 2.2 Mt N was emitted as N2O when using a non-linear response model, equivalent to 1.75% of the applied N.
  • Authors:
    • Greenhouse Gas Working Group
  • Year: 2010
  • Summary: Approximately 6% of all greenhouse gas (GHG) emissions originating in the United States (U.S.) come from agricultural activities.1 These gases are in the form of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). However, by employing proper management techniques, agricultural lands can both sequester carbon and reduce CO2, CH4, and N2O emissions, thereby reducing their GHG footprint. Cap-and-trade climate change legislation, currently under discussion in the legislative and executive branches, may have broad and long-term implications for the agricultural sector. In order to determine the role of agriculture in GHG emissions and capture, a full life cycle accounting of GHG sources and sinks is needed. The American Society of Agronomy (ASA), Crop Science Society of America (CSSA), and Soil Science Society of America (SSSA) have examined the evidence for GHG emissions and sequestration typical of agricultural systems in six U.S. regions (Figure 1): • Northeast • Southeast • Corn Belt • Northern Great Plains • Pacific • Southern Great Plains This report summarizes current knowledge of GHG emissions and capture as influenced by cropping system, tillage management, and nutrient source. Additionally, topics requiring further research have been identified.
  • Authors:
    • Alluvione, F.
    • Del Grosso, S. J.
    • Halvorson, A. D.
  • 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 N2O emissions. The study objective was to compare N2O 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 N2O emissions from urea and ESN application were not different under CT-CC, but ESN reduced N2O emissions 49% compared with urea under NT-CC. Compared with urea, SuperU reduced N2O 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 N2O emissions from irrigated systems.
  • Authors:
    • Robertson, G. P.
    • Grace, P. R.
    • Millar, N.
    • Gehl, R. J.
    • Hoben, J. P.
  • Source: Global Change Biology
  • Volume: 17
  • Year: 2010
  • Summary: Row-crop agriculture is a major source of nitrous oxide (N2O) globally, and results from recent field experiments suggest that significant decreases in N2O emissions may be possible by decreasing nitrogen (N) fertilizer inputs without affecting economic return from grain yield. We tested this hypothesis on five commercially farmed fields in Michigan, USA planted with corn in 2007 and 2008.
  • Authors:
    • Kohei, U.
    • Ebel, R.
    • Horowitz, J.
  • Source: Economic Information Bulletin
  • Volume: 70
  • Year: 2010
  • Summary: Most U.S. farmers prepare their soil for seeding and weed and pest control through tillage-plowing operations that disturb the soil. Tillage practices affect soil carbon, water pollution, and farmers' energy and pesticide use, and therefore data on tillage can be valuable for understanding the practice's role in reaching climate and other environmental goals. In order to help policymakers and other interested parties better understand U.S. tillage practices and, especially, those practices' potential contribution to climate-change efforts, ERS researchers compiled data from the Agricultural Resource Management Survey and the National Resources Inventory-Conservation Effects Assessment Project's Cropland Survey. The data show that approximately 35.5 percent of U.S. cropland planted to eight major crops, or 88 million acres, had no tillage operations in 2009.
  • Authors:
    • Gottlieb, J.
    • Horowitz, J.
  • Source: Economic Brief Number 15
  • Year: 2010
  • Authors:
    • Dolan, M. S.
    • Wilson, M. L.
    • McNearney, M.
    • Rosen, C. J.
    • Venterea, R. T.
    • Hyatt, C. R.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: Irrigated potato (Solanum tuberosum L.) production requires large inputs of N, and therefore has high potential for N loss including emissions of N2O. Two strategies for reducing N loss include split applications of conventional fertilizers, and single applications of polymer-coated urea (PCU), both of which aim to better match the timing of N availability with plant demand. The objective of this 3-yr study was to compare N2O emissions and potato yields following a conventional split application (CSA) using multiple additions of soluble fertilizers with single preplant applications of two different PCUs (PCU-1 and PCU-2) in a loamy sand in Minnesota. Each treatment received 270 kg of fertilizer N ha-1 per season. An unfertilized control treatment was included in 2 of 3 yr. Tuber yields did not vary among fertilizer treatments, but N2O emissions were significantly higher with CSA than PCU-1. During 3 consecutive yr, mean growing season emissions were 1.36, 0.83, and 1.13 kg N2O-N ha-1 with CSA, PCU-1, and PCU-2, respectively, compared with emissions of 0.79 and 0.42 kg N2O-N ha-1 in the control. The PCU-1 released N more slowly during in situ incubation than PCU-2, although differences in N2O emitted by the two PCUs were not generally significant. Fertilizer-induced emissions were relatively low, ranging from 0.10 to 0.15% of applied N with PCU-1 up to 0.25 to 0.49% with CSA. These results show that N application strategies utilizing PCUs can maintain yields, reduce costs associated with split applications, and also reduce N2O emissions.
  • Authors:
    • Andrasko, K.
    • Bosquet, B.
  • Year: 2010
  • Authors:
    • Mikha,M. M.
    • Nielsen,D. C.
    • Halvorson,A. D.
    • Benjamin,J. G.
  • Source: Agronomy Journal
  • Volume: 102
  • Issue: 3
  • Year: 2010
  • Summary: Crop biomass has been proposed as a source stock for bioethanol production. Levels of crop residue removal must be determined to prevent degradation of soil physical and chemical properties resulting from soil organic carbon (SOC) loss. Carbon inputs from crop residues and an estimate of inputs from roots and rhizodeposition (C return) were calculated and compared with changes in SOC after seven cropping seasons at Akron, CO. Tillage treatments included a chisel plow (CP) and a no-till (NT) treatment. A crop rotation alternating grasses and broadleaf crops was compared with continuous corn ( Zea mays L.). Irrigation treatments included water application to meet evapotranspiration demand or application only during the reproductive stage of each crop. Total C return varied from 25 Mg ha -1 for the delayed irrigation, crop rotation plots to 63 Mg ha -1 for the fully irrigated, continuous corn plots. The change in SOC in the surface 30 cm of soil varied from -0.8 Mg SOC ha -1 for the rotation plots to a gain of 2.8 Mg ha -1 for the continuous corn plots after 7 yr. Correlating crop residue input with change in SOC showed that about 4.6 Mg ha -1 yr -1 C return is needed to maintain SOC levels for NT cropping systems and an average of 7.4 Mg ha -1 yr -1 C return is needed to maintain SOC levels under chisel tillage. Continuous corn was the only system that consistently provided sufficient crop residue to maintain SOC levels. Residue removal for off-farm use should consider only amounts that can be harvested without decreasing SOC levels.
  • Authors:
    • Barfoot, P.
    • Brookes, G.
  • Source: AgBioForum
  • Volume: 13
  • Issue: 1
  • Year: 2010
  • Summary: This article updates the assessment of the impact commercialized agricultural biotechnology is having on global agriculture from an environmental perspective. It focuses on the impact of changes in pesticide use and greenhouse gas emissions arising from the use of biotech crops. The technology has reduced pesticide spraying by 352 million kg (-8.4%) and, as a result, decreased the environmental impact associated with herbicide and insecticide use on these crops (as measured by the indicator the environmental impact quotient) by 16.3%. The technology has also significantly reduced the release of greenhouse gas emissions from this cropping area, which, in 2008, was equivalent to removing 6.9 million cars from the roads.