• Authors:
    • Bourbonniere, R. A.
    • Macrae, M. L.
    • DeSimone, J.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 138
  • Issue: 1-2
  • Year: 2010
  • Summary: Riparian zones often serve to buffer nutrient loading from agricultural uplands but may also release greenhouse gases such as nitrous oxide (N2O) to the atmosphere. Riparian zone topography, combined with lateral chemical inputs from fields, is expected to cause variable hydrochemical environments which may lead to spatially variable N2O emissions. We examined spatial patterns in the simultaneous measurements of subsurface nutrient supply in groundwater, subsurface N2O production and surface N2O fluxes along two transects across a forested riparian zone adjacent to an agricultural field. Although subsurface N2O concentrations and ground water nitrate (NO3-) concentrations displayed distinct spatial trends across the riparian zone, with larger concentrations near the riparian zone-field interface and smaller concentrations in the riparian zone interior, surface N2O fluxes did not reflect this pattern. Instantaneous N2O fluxes measured during this study ranged from -0.28 to 1.3 nmolm-2 s-1 and were as variable within a site as they were among sites. Surface N2O fluxes were most strongly correlated with air and soil temperatures and N2O concentrations in soil pores in the top 15 cm of the soil profile, and were generally not correlated with conditions found in deeper soil throughout the riparian zone, suggesting that lateral inputs in runoff from the agricultural uplands are not increasing N2O fluxes at this site. Further research and analysis is required for a better understanding of the production and consequent movement of N2O, as well as an improved understanding of the effects of agriculture on N2O emissions from riparian areas.
  • Authors:
    • Mauder, M.
    • MacPherson, J. I.
    • Srinivasan, R.
    • Grant, B.
    • Worth, D.
    • Smith, W. N.
    • Pattey, E.
    • Desjardins, R. L.
  • Source: Agricultural and Forest Meteorology
  • Volume: 150
  • Issue: 6
  • Year: 2010
  • Summary: Nitrous oxide (N2O) emissions are a large proportion of the agriculture sector's contribution to the greenhouse gas inventory of most developed countries. The spatial and temporal variability of N2O emissions from agricultural soils has long been considered the main factor limiting our ability to estimate N2O emissions, particularly the emissions associated with the spring snowmelt period. Tower and aircraft-based flux measurement systems and a process-based model were used to quantify N2O emissions for four years (2000, 2001, 2003 and 2004) in an agricultural area of eastern Canada, near Ottawa, where a corn-soybean crop rotation dominates. A tower-based system, which relies on the flux gradient technique, provided diurnal N2O emissions at a field scale. An aircraft-based system, which relies on the relaxed eddy accumulation technique, provided N2O emissions for two similar agricultural regions and the denitrification and decomposition (DNDC) model was used to estimate daily N2O emissions at a regional scale. In most cases, aircraft-based N2O emissions measurements were comparable for the two agricultural regions. Corresponding tower-based measurements which were collected over a field in the Ottawa area showed similar emission patterns to the aircraft-based measurements but in some cases the tower-based emissions were larger, as expected. This is because the footprint of aircraft-based measurements always incorporated a significant amount of crops such as soybean and other types of vegetation which do not receive additional nitrogen fertilization as well as waterlogged areas that do not emit N2O. While in three of the four years, the tower-based measurements were made over a tile drained field where nitrogen fertilizer had been applied the previous year. The N2O emissions patterns after planting were also similar for both aircraft and tower-based systems, but again they were slightly larger for the tower-based system. Aircraft-based N2O flux measurements are also compared to the N2O emissions obtained using the most recent version of the process-based model DNDC. Tests showed that DNDC gave comparable N2O emissions estimates for the measurement period as a whole, but was not always able to correctly predict the timing of peak emissions.
  • Authors:
    • Dilling, L.
    • Failey, E. L.
  • Source: Environmental Research Letters
  • Volume: 5
  • Issue: 2
  • Year: 2010
  • Summary: Land use and its role in reducing greenhouse gases is a key element of policy negotiations to address climate change. Calculations of the potential for enhanced terrestrial sequestration have largely focused on the technical characteristics of carbon stocks, such as vegetation type and management regime, and to some degree, on economic incentives. However, the actual potential for carbon sequestration critically depends on who owns the land and additional land management decision drivers. US land ownership patterns are complex, and consequently land use decision making is driven by a variety of economic, social and policy incentives. These patterns and incentives make up the 'carbon stewardship landscape'-that is, the decision making context for carbon sequestration. We examine the carbon stewardship landscape in the US state of Colorado across several public and private ownership categories. Achieving the full potential for land use management to help mitigate carbon emissions requires not only technical feasibility and financial incentives, but also effective implementing mechanisms within a suite of often conflicting and hard to quantify factors such as multiple-use mandates, historical precedents, and non-monetary decision drivers.
  • Authors:
    • Franzluebbers, A. J.
  • Source: Soil Organic Matter and Nutrient Cycling to Sustain Agriculture in the Southeastern USA
  • Year: 2010
  • 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:
    • Scholz, V.
    • Kern, J.
    • Strähle, M.
    • Hellebrand, H. J.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 87
  • Issue: 2
  • Year: 2010
  • Summary: Carbon (C) sequestration and soil emissions of nitrous oxide (N2O) affect the carbon dioxide (CO2) advantage of energy crops. A long-term study has been performed to evaluate the environmental effects of energy crop cultivation on the loamy sand soil of the drier northeast region of Germany. The experimental field, established in 1994, consisted of columns (0.25 ha each) cultivated with short rotation coppice (SRC: Salix and Populus) and columns cultivated with annual crops. The columns were subdivided into four blocks, with each receiving different fertilization treatments. The soil C content was measured annually from 1994 until 1997, and then in 2006. Soil N2O levels were measured several times per week from 1999 to 2007. Water-filled pore space (WFPS) and soil nitrate measurements have been performed weekly since 2003. Increased C stocks were found in SRC columns, and C loss was observed in blocks with annual crops. The soil from fertilized blocks had higher levels of C than the soil from non-fertilized blocks. SRC cropping systems on dry, loamy sand soils are advantageous relative to annual cropping systems because of higher C sequestration, lower fertilized-induced N2O emissions, and reduced background N2O emissions in these soils. SRC cropping systems on dry, loamy sand soils have a CO2 advantage (approximately 4 Mg CO2 ha(-1) year(-1)) relative to annual cropping 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:
    • Song, C. C.
    • Su, Y. H.
    • Yu, Y. Q.
    • Zhang, W.
    • Sun, W. J.
    • Huang, Y.
  • Source: Global Change Biology
  • Volume: 16
  • Issue: 2
  • Year: 2010
  • Summary: It has been well recognized that converting wetlands to cropland results in loss of soil organic carbon (SOC), while less attention was paid to concomitant changes in methane (CH4) and nitrous oxide (N2O) emissions. Using datasets from the literature and field measurements, we investigated loss of SOC and emissions of CH4 and N2O due to marshland conversion in northeast China. Analysis of the documented crop cultivation area indicated that 2.91 Mha of marshland were converted to cropland over the period 1950-2000. Marshland conversion resulted in SOC loss of similar to 240 Tg and introduced similar to 1.4 Tg CH4 and similar to 138 Gg N2O emissions in the cropland, while CH4 emissions reduced greatly in the marshland, cumulatively similar to 28 Tg over the 50 years. Taking into account the loss of SOC and emissions of CH4 and N2O, the global warming potential (GWP) at a 20-year time horizon was estimated to be similar to 180 Tg CO2_eq. yr-1 in the 1950s and similar to 120 Tg CO2_eq. yr-1 in the 1990s, with a similar to 33% reduction. When calculated at 100-year time horizon, the GWP was similar to 73 Tg CO2 _eq. yr-1 in the 1950s and similar to 58 Tg CO2_eq. yr-1 in the 1990s, with a similar to 21% reduction. It was concluded that marshland conversion to cropland in northeast China reduced the greenhouse effect as far as GWP is concerned. This reduction was attributed to a substantial decrease in CH4 emissions from the marshland. An extended inference is that the declining growth rate of atmospheric CH4 since the 1980s might be related to global loss of wetlands, but this connection needs to be confirmed.
  • 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.