• 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:
    • 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:
    • Schlegel, A. J.
    • Stone, L. R.
  • Source: Agronomy Journal
  • Volume: 102
  • Issue: 2
  • Year: 2010
  • Summary: Efficient water use is the primary determinant of profitability in dryland crop production of the western Great Plains. For a sustainable increase in precipitation use efficiency (PUE) from that typical of the traditional winter wheat (Triticum aestivum L.)-fallow rotation with conventional stubble-mulch (sweep) tillage (CT) to occur, decreased use of fallow and tillage is required. Our objective was to quantify the effect of tillage intensity (no-till [NT], reduced tillage [RT], and CT) and phase of the winter wheat-grain sorghum [Sorghum bicolor (L.) Moench]-fallow rotation on selected sod properties that influence PUE, with emphasis on infiltration and the association between water-stable aggregates (WSA) and infiltration rate. Soil water content at -1.5 MPa matric potential, concentration of WSA >= 0.5 mm, mean weight diameter of WSA, and ponded steady-state infiltration rate were significantly greater with NT than RT or CT (infiltration rates: NT, 30.6; RT, 15.3; and CT, 11.4 mm h(-1)). Infiltration rate was significantly greater in the wheat phase (25.8 mm h(-1)) than in the sorghum (15.4 mm h(-1)) or fallow (16.2 mm h(-1)) phases. The significantly better conditions of aggregate stability and water infiltration with NT management and the lack of development of poor infiltration properties during the wheat season that would need to be alleviated by tillage after harvest reinforce the appropriateness of NT management in crop production systems of the region.
  • Authors:
    • Gross, J. R.
    • Tanaka, D. L.
    • Liebig, M. A.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: The inclusion of cover crops during fallow (i.e., green fallow) may mitigate greenhouse gas (GHG) emissions from dryland cropping systems. An investigation was conducted to quantify the effects of chemical and green fallow on soil organic C (SOC) and CO2, CH4, and N2O flux within spring wheat (Triticum aestivum L.)-fallow (chemical fallow) and spring wheat-safflower (Carthamus tinctorius L.)-rye (Secale cereale L.) (green fallow) under no-till management in west-central North Dakota. Using static chamber methodology, flux measurements were made during 19 mo of the fallow period of each cropping system. Soil samples collected before initiation of flux measurements indicated no difference in SOC in the surface 10 cm between cropping systems. Additionally, differences in gas flux between cropping systems were few. Emission of CO2 was greater under green fallow than chemical fallow during spring thaw until the termination of rye (P = 0.0071). Uptake of atmospheric CH4 was the dominant exchange process during the evaluation period, and was significantly (P = 0.0124) greater under chemical fallow (-2.7 g CH4-C ha-1 d-1) than green fallow (-1.5 g CH4-C ha-1 d-1) following the termination of rye. Cumulative fluxes of CO2, CH4, and N2O did not differ between the chemical- and green-fallow phases during the 19-mo period (P = 0.1293, 0.2629, and 0.9979, respectively). The results from this evaluation suggest there was no net GHG benefit from incorporating a rye cover crop during the fallow phase of a dryland cropping system under no-till management.
  • Authors:
    • Robertson, G. P.
    • Grace, P. R.
    • Bohm, S.
    • McSwiney, C. P.
  • Source: Journal of Natural Resources and Life Sciences Education
  • Volume: 39
  • Year: 2010
  • Summary: Opportunities for farmers to participate in greenhouse gas (GHG) credit markets require that growers, students, extension educators, offset aggregators, and other stakeholders understand the impact of agricultural practices on GHG emissions. The Farming Systems Greenhouse Gas Emissions Calculator, a web-based tool linked to the SOCRATES soil carbon process model, provides a simple introduction to the concepts and magnitudes of gas emissions associated with crop management. Users choose a county of interest on an introductory screen and are taken to the input/output window, where they choose crops, yields, tillage practices, or nitrogen fertilizer rates. Default values are provided based on convention and county averages. Outputs include major contributors of greenhouse gases in field crops: soil carbon change, nitrous oxide (N2O) emission, fuel use, and fertilizer. We contrast conventional tillage and no-till in a corn-soybean-wheat (Zea mays L.-Glycine max (L.) Merr.-Triticum aestivum L.) rotation and compare continuous corn fertilized at 101 and 134 kg N ha-1 yr-1. In corn years, N2O was the dominant GHG, due to high fertilizer requirements for corn. No-till management reduced greenhouse gas emissions by 50% due to net soil carbon storage. Continuous corn fertilized at 101 kg N ha-1 yr-1 emitted 1.25 Mg CO2 equivalents ha-1 yr-1 compared with 1.42 Mg CO2 equivalents ha-1 yr-1 at 134 kg N ha-1 yr-1, providing a 12% GHG savings. The calculator demonstrates how cropping systems and management choices affect greenhouse gas emissions in field crops.
  • 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:
    • Rosegrant, M.
    • Derner, J. D.
    • Schuman, G. E.
    • Verchot, L.
    • Steinfeld, H.
    • Gerber, P.
    • De Freitas, P. L.
    • Lal, R.
    • Desjardins, R. L.
    • Dumanski, J.
  • Source: Applied Agrometeorology
  • Year: 2010
  • Summary: Agriculture can make significant contributions to climate change mitigation by (a) increasing soil organic carbon (SOC) sinks, (b) reducing GHG emissions, and (c) off-setting fossil fuel by promoting biofuels. The latter has the potential to counter-balance fossil fuel emissions to some degree, but the overall impact is still uncertain compared to emissions of non-CO2 GHGs, which are likely to increase as production systems intensify. Agricultural lands also remove CH4 from the atmosphere by oxidation, though less than forestlands (Tate et al. 2006; Verchot et al. 2000), but this effect is small compared to other GHG fluxes (Smith and Conen 2004).
  • Authors:
    • Franzluebbers,A. J.
  • Source: Soil Science Society of America Journal
  • Volume: 74
  • Issue: 2
  • Year: 2010
  • Summary: Conservation management of degraded land has the potential to build soil fertility, restore soil functions, and mitigate greenhouse gas emissions as a consequence of surface soil organic matter accumulation. Literature from the southeastern United States was reviewed and synthesized to: (i) quantitatively evaluate the magnitude and rate of soil organic C (SOC) sequestration with conservation agricultural management; (ii) evaluate how conservation management affects surface SOC accumulation and its implications on ecosystem services; and (iii) recommend practical soil sampling strategies based on spatial and temporal issues to improve the detection of statistically significant SOC sequestration. Soil organic C sequestration was 0.45 ± 0.04 Mg C ha-1 yr-1 (mean ± standard error, n = 147, 20 ± 1 cm depth, 11 ± 1 yr) with conservation tillage compared with conventional tillage cropland. Establishment of perennial pastures sequestered 0.84 ± 0.11 Mg C ha-1 yr-1 (n = 35, 25 ± 2 cm depth, 17 ± 1 yr). Stratification of SOC with depth was common under conservation agricultural management and appears to be integrally linked to abatement of soil erosion, improvement in water quality, and SOC sequestration. Sampling of conservation management systems should ideally occur repeatedly with time in controlled and replicated experiments, but there is also an urgent need for chronosequence and paired-field surveys of SOC on working farms in the region to validate and expand the scope of inference of experimental results. Landowners in the southeastern United States have great potential to restore soil fertility and mitigate greenhouse gas emissions with the adoption of and improvement in conservation agricultural systems (e.g., continuous no-till, high-residue crop rotations, high organic matter inputs).
  • Authors:
    • Franzluebbers, A. J.
  • Year: 2010
  • 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.