• Authors:
    • Felzer, B. S.
  • Source: Ecological Modelling
  • Volume: 240
  • Issue: August
  • Year: 2012
  • Summary: Future climate projections indicate that Pennsylvania will get significantly warmer and wetter due to continued increases in atmospheric greenhouse gas (GHG) concentrations. Using the Terrestrial Ecosystem Model version Hydro2 (TEM-Hydro2), this study explores the effect of different climate and land use scenarios on carbon, nitrogen, and water dynamics during the 20th and 21st centuries. TEM-Hydro2 runs are forced by historical 20th century climate data and by 21st century climate projections from the NCAR CCSM3.0 IPCC A2 and B1 scenarios, a relatively high and low GHG emissions scenario, respectively. Regrowing forests are the only ecosystem with positive Net Carbon Exchange (NCE) and sequestered more than 12,000 g C m(-2) during the 20th century. The highest rates of leaching of dissolved inorganic nitrogen (DIN) occurred in fertilized croplands in the 20th century. Twenty first century runoff increases by 30% in the A2 scenario and 20% in the B1 scenario, but DIN leaching only increases in the A2 scenario. DIN leaching depends upon both runoff and available inorganic nitrogen, which decreases due to high productivity and enhanced plant nitrogen uptake. The effect of increasing urbanization in the 21st century is to reduce NCE by about 34% in both climate scenarios, while water runoff increases by 5% and DIN leaching decreases by 17%. The reduced leaching is the result of converting agricultural land to suburban areas, which are a combination of turflawn and forests, both of which have lower leaching rates than croplands or pastures. Incorporating realistic forest stand age substantially increases the NCE but has little effect on runoff or DIN leaching. Maize yields decrease in the A2 scenario due to the excessive leaching, but increase in the B1 scenario. These results illustrate why it is important to include scenarios of both GHG emissions and realistic land use changes in model projections of the regional impacts of climate change in the 21st century. (C) 2012 Elsevier B.V All rights reserved.
  • Authors:
    • Hubbs, M. D.
    • Franzluebbers, A. J.
    • Norfleet, M. L.
  • Source: Journal of Soil and Water Conservation
  • Volume: 67
  • Issue: 5
  • Year: 2012
  • Summary: Simulation models that are sensitive to management, edaphic factors, and climate could provide insights into how land owners and producers might be able to sequester soil organic carbon (C) and engage in emerging carbon markets. In this study, the soil conditioning index (SCI) embedded in the Revised Universal Soil Loss Equation (RUSLE2) model was used to predict (1) potential soil organic C sequestration under conventional and conservation management of a diversity of cotton cropping systems throughout the Cotton Belt and (2) relative influences of soil texture, slope, climatic conditions, and management on potential soil organic C sequestration. Across 10 regions of the Cotton Belt, SCI scores ranked in the following order: perennial pasture > no-till cropping systems > conventional tillage cotton. Variations in significance of SCI scores occurred among 5 different no-till cropping systems within regions of the Cotton Belt. For example, 7 of the 10 regions had significantly (p <= 0.05) greater SCI scores (linked to greater soil organic C sequestration) when monoculture cotton was grown with winter cover crop than without.Variation in SCI was dominated by management (46%) and slope (24%) and very little affected by climate (7%) and soil texture (1%). Increasingly wetter climatic conditions (as expressed by increasing precipitation to potential evapotranspiration) had a negative influence on SCI scores for all management systems and land slopes evaluated, but particularly for moldboard-plowed cotton on sloping land, With a linear relationship between SCI and soil organic C sequestration, predicted soil organic C sequestration averaged -0.31 +/- 0.19 Mg C ha(-1) y(--1) (-280 +/- 170 lb ac(-1) yr(-1)) under conventionally tilled cotton, 0.12 +/- 0.06 Mg C ha(-1) y(-1) (103 +/- 52 lb ac(-1) yr(-1)) under various no-till crop rotations, and 0.26 +/- 0.02 Mg C ha(-1) y(-1) (231 +/- 20 lb ac(-1) yr(-1)) under perennial pasture. Cotton production with conventional tillage could only be expected to maintain soil organic C under a best-case scenario and would lose substantial soil organic C under most other scenarios. Simulations showed the strong, positive influence that conservation agricultural management has to sequester soil organic C, irrespective of climate, slope, and texture.
  • Authors:
    • Tsegaye, T. D.
    • Loescher, H. W.
    • Gebremedhin, M. T.
  • Source: Agronomy Journal
  • Volume: 104
  • Issue: 5
  • Year: 2012
  • Summary: The southeastern United States is an economically important agricultural region, yet its role in the regional C budget is not fully understood. There is concern that climate change, particularly altered precipitation patterns, may induce a shift in how crops exchange CO2 with the atmosphere. This study examined the seasonal and interannual variation in net ecosystem exchange (NEE) of a winter wheat cover crop (Triticum aestivum L.) and soybean [Glycine max (L.) Merr.] using the eddy covariance (EC) method. This was conducted at Winfred Thomas Agricultural Research Station, Hazel Green, AL (2007-2009). Annual C balance ranged from a source in 2007 (NEE = 100 g C m(-2) yr(-1)) to a sink (-20 g C m(-2) yr(-1)) in 2009. Annual ecosystem respiration (Re) ranged between 750 and 1013 g C m(-2) yr(-1), while gross ecosystem productivity was between 650 and 1034 g C m(-2) yr(-1). Seasonal NEE for soybean ranged between 42 and -66 g C m(-2). The uptake rates from the cover crop (NEE = -80.0, -80.4, and -40.0 g C m(-2) for 2007, 2008, and 2009, respectively) suggested the importance of winter C uptake off setting C losses caused by summer droughts. The R-e varied between 286 and 542 g C m(-2) for soybean and between 160 and 313 g C m(-2) for the cover crop. Annual variations in NEE and R-e were primarily due to precipitation and air temperature, respectively, indicating a tight coupling between biophysical factors and C uptake. Our results were compared with those from other reported NEE crop estimates using EC.
  • Authors:
    • Negri, M. C.
    • Gopalakrishnan, G.
    • Salas, W.
  • Source: GCB Bioenergy
  • Volume: 4
  • Issue: 6
  • Year: 2012
  • Summary: Current research on the environmental sustainability of bioenergy has largely focused on the potential of bioenergy crops to sequester carbon and mitigate greenhouse gas emissions and possible impacts on water quality and quantity. A key assumption in these studies is that bioenergy crops will be grown in a manner similar to current agricultural crops such as corn and hence would affect the environment similarly. In this study, we investigate an alternative cropping system where bioenergy crops are grown in buffer strips adjacent to current agricultural crops such that nutrients present in runoff and leachate from the traditional row-crops are reused by the bioenergy crops (switchgrass, miscanthus and native prairie grasses) in the buffer strips, thus providing environmental services and meeting economic needs of farmers. The process-based biogeochemical model Denitrification-Decomposition (DNDC) was used to simulate crop yield, nitrous oxide production and nitrate concentrations in leachate for a typical agricultural field in Illinois. Model parameters have been developed for the first time for miscanthus and switchgrass in DNDC. Results from model simulations indicated that growing bioenergy crops in buffer strips mitigated nutrient runoff, reduced nitrate concentrations in leachate by 60-70% and resulted in a reduction of 50-90% in nitrous oxide emissions compared with traditional cropping systems. While all the bioenergy crop buffers had significant positive environmental benefits, switchgrass performed the best with respect to minimizing nutrient runoff and nitrous oxide emissions, while miscanthus had the highest yield. Overall, our model results indicated that the bioenergy crops grown in these buffer strips achieved yields that are comparable to those obtained for traditional agricultural systems while simultaneously providing environmental services and could be used to design sustainable agricultural landscapes.
  • Authors:
    • Cassman, K. G.
    • Grassini, P.
  • Source: Proceedings of the National Academy of Sciences of the United States of America
  • Volume: 109
  • Issue: 4
  • Year: 2012
  • Summary: Addressing concerns about future food supply and climate change requires management practices that maximize productivity per unit of arable land while reducing negative environmental impact. On-farm data were evaluated to assess energy balance and greenhouse gas (GHG) emissions of irrigated maize in Nebraska that received large nitrogen (N) fertilizer (183 kg of N.ha(-1)) and irrigation water inputs (272 mm or 2,720 m(3) ha(-1)). Although energy inputs (30 GJ.ha(-1)) were larger than those reported for US maize systems in previous studies, irrigated maize in central Nebraska achieved higher grain and net energy yields (13.2 Mg.ha(-1) and 159 GJ.ha(-1), respectively) and lower GHG-emission intensity (231 kg of CO(2)e center dot Mg-1 of grain). Greater input-use efficiencies, especially for N fertilizer, were responsible for better performance of these irrigated systems, compared with much lower-yielding, mostly rainfed maize systems in previous studies. Large variation in energy inputs and GHG emissions across irrigated fields in the present study resulted from differences in applied irrigation water amount and imbalances between applied N inputs and crop N demand, indicating potential to further improve environmental performance through better management of these inputs. Observed variation in N-use efficiency, at any level of applied N inputs, suggests that an N-balance approach may be more appropriate for estimating soil N2O emissions than the Intergovernmental Panel on Climate Change approach based on a fixed proportion of applied N. Negative correlation between GHG-emission intensity and net energy yield supports the proposition that achieving high yields, large positive energy balance, and low GHG emissions in intensive cropping systems are not conflicting goals.
  • Authors:
    • Del Grosso, S.
    • Halvorson, A.
  • Source: Journal of Environmental Quality
  • Volume: 41
  • Issue: 5
  • Year: 2012
  • Summary: A nitrogen (N) source comparison study was conducted to further evaluate the effects of inorganic N source and placement on growing-season and non-crop period soil nitrous oxide (N2O). Commercially available controlled-release N fertilizers were evaluated for their potential to reduce N2O emissions from a clay loam soil compared with conventionally used granular urea and urea-ammonium nitrate (UAN) fertilizers in an irrigated no-till (NT) corn (Zea mays L.) production system. Controlled-release N fertilizers evaluated were: a polymer-coated urea (ESN), stabilized urea (SuperU), and UAN+AgrotainPlus (SuperU and AgrotainPlus contain nitrification and urease inhibitors). Each N source was surface band applied (202 kg N ha(-1)) near the corn row at emergence and watered into the soil the next day. Subsurface banded ESN (ESNssb) and check (no N applied) treatments were included. Nitrous oxide fluxes were measured during two growing seasons and aft er harvest using static, vented chambers. All N sources had significantly lower growing-season N2O emissions than granular urea (0.7% of applied N), with UAN+AgrotainPlus (0.2% of applied N) and ESN (0.3% of applied N) having lower emissions than UAN (0.4% of applied N). Similar trends were observed when expressing N2O emissions on a grain yield and N uptake basis. Corn grain yields were not different among N sources but were greater than the check. Selection of N fertilizer source can be a mitigation practice for reducing N2O emissions in NT, irrigated corn in semiarid areas. In our study, UAN+AgrotainPlus consistently had the lowest level of N2O emissions with no yield loss.
  • Authors:
    • Parkin, T.
    • Hatfield, J.
  • Source: Agricultural Sciences
  • Volume: 3
  • Issue: 8
  • Year: 2012
  • Summary: Spatial variation of soil carbon dioxide (CO 2) flux during a growing season within corn and soybean canopies has not been quantified. These cropping systems are the most intense in the United States and the potential for carbon (C) sequestration in these systems through changes in soil management practices create an opportunity for reduction in greenhouse gas emissions; however, the need to understand the variation in fields is critical to evaluating changes in management systems. A study was designed to evaluate the spatial variation in soil CO 2 fluxes along two transects in corn and soybean fields. Samples were collected every 5 m along a 100 m transect between the rows of the crop and also along a transect in which the plants had been removed to reduce the potential of root respiration. Soil CO 2 fluxes were collected at each position with air temperature, soil temperature at 0.05 m, and soil water content (0-0.06 m). At the end of the season, soil samples for the upper 0.1 m were collected for soil organic C content, pH, sand, silt, and clay contents. On each day measurements were made, the observed CO 2 emissions were scaled by dividing the CO 2 flux at each position by the mean CO 2 flux of the entire transect. Observed CO 2 fluxes were signifycantly larger in the row than in the fallow position for both crops. There were no differences between the corn and soybean fallow transects; however, the corn row samples were larger than the soybean row samples. No consistent spatial patterns were observed in the CO 2 fluxes or any of the soil properties over the course of the study. When the CO 2 flux data were combined over the season, there was a significant spatial pattern in the fallow transects for both crops but not for the row transects. Sampling for CO 2 flux values in cropping systems has to consider the presence of a crop canopy and the amount of root respiration.
  • Authors:
    • Dukes, J.
    • Hoeppner, S.
  • Source: Global Change Biology
  • Volume: 18
  • Issue: 5
  • Year: 2012
  • Summary: As Earth's atmosphere accumulates carbon dioxide (CO2) and other greenhouse gases, Earth's climate is expected to warm and precipitation patterns will likely change. The manner in which terrestrial ecosystems respond to climatic changes will in turn affect the rate of climate change. Here we describe responses of an old-field herbaceous community to a factorial combination of four levels of warming (up to 4 degrees C) and three precipitation regimes (drought, ambient and rain addition) over 2 years. Warming suppressed total production, shoot production, and species richness, but only in the drought treatment. Root production did not respond to warming, but drought stimulated the growth of deeper (> 10 cm) roots by 121% in 1 year. Warming and precipitation treatments both affected functional group composition, with C4 grasses and other annual and biennial species entering the C3 perennial-dominated community in ambient rainfall and rain addition treatments as well as in warmed treatments. Our results suggest that, in this mesic system, expected changes in temperature or large changes in precipitation alone can alter functional composition, but they have little effect on total herbaceous plant growth. However, drought limits the capacity of the entire system to withstand warming. The relative insensitivity of our study system to climate suggests that the herbaceous component of old-field communities will not dramatically increase production in response to warming or precipitation change, and so it is unlikely to provide either substantial increases in forage production or a meaningful negative feedback to climate change later this century.
  • Authors:
    • Garcia, L. A.
    • Ahuja, L. R.
    • Islam, A.
    • Ma, L.
    • Saseendran, A. S.
  • Source: Web Of Knowledge
  • Volume: 55
  • Issue: 6
  • Year: 2012
  • Summary: Changes in evapotranspiration demand due to global warming will have a profound impact on irrigation water demand and agricultural productivity. In this study, the effects of possible future anthropogenic climate change on reference evapotranspiration (ETo) were evaluated using the Penman-Monteith equation. The combined effect of temperature and elevated CO2 concentrations on ETo was the major focus of this study. The ETo under the General Circulation Model (GCM) projected climate change scenarios was estimated for a location in Colorado. Multi-model ensemble climate change scenarios were generated from 112 Bias Corrected and Spatially Disaggregated (BCSD) projections from the World Climate Research Program (WCRP) archive, which cover different levels of greenhouse gas emissions. Results showed a decrease in ETo demand with increases in CO2 levels, which greatly moderated the increase in ETo due to increasing temperature. The effect of increases in CO2 levels up to 450 ppm off set the effect of about 1 degrees C rise in temperature. Simulation results with projected climate change scenarios, without considering the effects of CO2 levels, showed an 8.3%, 14.7% and 21.0% increase in annual ETo during the 2020s, 2050s, and 2080s, respectively, when simulation was carried out using an ensemble of the 112 projections. When the effect of elevated CO2 levels was also considered in combination with projected changes in temperature, changes in annual ETo demand varied from -1.5% to 5.5%, -10.4% to 6.7%, and -19.7% to 6.6% during the 2020s, 2050s, and 2080s, respectively, depending on the different climate change scenarios considered and the relationship or equation used for estimating the effect of elevated CO2 on stomatal resistance term in the Penman-Monteith equation.
  • Authors:
    • Barbour, N. W.
    • Archer, D. W.
    • Weyers, S. L.
    • Johnson, J. M. F.
  • Source: Soil Science Society of America Journal
  • Volume: 76
  • Issue: 4
  • Year: 2012
  • Summary: Empirical data on methane (CH4) and nitrous oxide (N2O) emission are needed for management systems from many regions of the United States to evaluate mitigation strategies. The primary objectives of this study were to assess and compare crop productivity, CH4 andN(2)O flux, and yield-scaled emissions between a conventionally and an organically managed system. All phases of a corn (Zea mays L.)-soybean [Glycine max L. (Merr.)]-wheat (Triticum aestivum L.) over alfalfa (Medicago sativa L.)-alfalfa rotation were present each year. Both systems emitted about 4.2 kg N2O-N ha(-1) yr(-1) including growing and nongrowing season emissions, which cumulatively represents 4.74 and 9.26% of 267 kg synthetic-N and 136 kg manure-N applied, respectively. The equivalent of 0.84% of the 78 kg urea-N and 0.76% of the 136 kg manure-N were emitted as N2O ha(-1) within 30-d of fertilizer application in the conventionally managed system and organically managed system, respectively. Following the application of starter fertilizer to the conventionally managed corn, the equivalent of 3.45% of the 11 kg starter N was emitted within 30 d. The largest spring-thaw N2O flux was measured in the conventionally managed system following alfalfa, which had been killed the previous fall. Yield-scaled N2O+CH4 emission (Mg CO2 equivalents Mg-1 yield) was 1.6- to 5-times greater in the organically managed system, which had lower yield but similar emission compared to the conventionally managed system. Thus, viability of organic systems to mitigate greenhouse gas (GHG) emission may be compromised when crop productivity is reduced. Study results highlight the importance of assessing emission and crop production when evaluating GHG mitigation strategies.