• Authors:
    • Morgan, J. A.
    • Ellis, D. D.
    • LeCain, D. R.
    • Alves, A. A. C.
    • Cruz, J. L.
  • Source: Plant and Soil
  • Volume: 374
  • Issue: 1-2
  • Year: 2014
  • Summary: This study evaluated how different nitrogen forms affect growth and photosynthetic responses of cassava to CO2 concentration. Cassava was grown in 14-L pots in a greenhouse at 390 or 750 ppm of CO2. Three nitrogen treatments were applied: (a) 12 mM NO3 (-), (b) 6 mM NO3 (-) + 6 mM NH4 (+), and (c) 12 mM NH4 (+). Thirty-six days after treatments began, plants grown under elevated CO2 and fertilized only with NO3 (-) (750_NO3 (-)) had photosynthetic rates similar to plants grown under 390_NO3 (-), indicating significant photosynthetic acclimation to CO2. In contrast, photosynthetic rates at elevated CO2 increased as NH4 (+) increased in the nutrient solution, such that photosynthetic acclimation was reduced for plants fertilized with only NH4 (+). However, this positive effect of NH4 (+) on photosynthesis was not observed in more advanced growth stages, and the toxic effects of NH4 (+) severely reduced total dry mass for these plants measured at the end of the experiment. Our results indicate that cassava will respond with increased biomass accumulation in response to raising atmospheric CO2 levels, and that N form can have an important impact on the photosynthetic response. However, the positive effect of NH4 (+) fertilization on cassava photosynthetic CO2 response eventually led to a toxicity problem that reduced biomass production. The challenge is to determine how to manage NH4 (+) fertilization so that the photosynthetic benefit observed in the initial phase may persist throughout the crop cycle.
  • Authors:
    • Schmidt, J.
    • Bryant, R.
    • Han, K.
    • Dell, C.
  • Source: American Society of Agronomy
  • Volume: 106
  • Issue: 2
  • Year: 2014
  • Summary: The use of enhanced efficiency N fertilizers can increase crop N utilization and lead to lower emissions of the greenhouse gas N2O. To determine the potential benefit of four enhanced efficiency fertilizers with rainfed corn (Zea mays L.) production in central Pennsylvania, N2O emissions and grain yield were monitored during a 4-yr field study and compared with untreated urea prills and urea-NH4NO3 (UAN). The tested enhanced efficiency products were ESN (polymer-coated urea), SuperU (urease and nitrification inhibitor treated urea), UAN treated with AgrotainPlus (urease and nitrification inhibitors), and PiNT (cation-stabilized amine-N). Additionally, 28-d laboratory incubations were conducted to verify the potential differences in N cycling rates among N sources. The laboratory incubations indicated that ESN, SuperU, and treated UAN all had the potential to delay accumulation of NO3 relative to untreated urea and UAN, but N cycling was similar with PiNT and the untreated fertilizers. Extended dry periods limited the denitrification potential and overall N2O emissions in the field, but spikes of N2O emission were seen within 1 mo after fertilizer application in each year. However, variation in emission rates was high within treatments, and no consistent differences among N sources were seen. Cumulative growing season N2O emissions and grain yield were similar for all N sources in each year of the study. Enhanced efficiency fertilizers do not appear to be an effective means to reduce N2O emission in a rainfed system, at least when rainfall is inconsistent.
  • Authors:
    • Wienhold, B.
    • Schmer, M.
    • Venterea, R.
    • Varvel, G.
    • Stott, D.
    • Sauer, T.
    • Osborne, S.
    • Lehman, R.
    • Karlen, D.
    • Johnson, J.
    • Baker, J.
    • Jin, V.
  • Source: Bioenergy Research
  • Volume: 7
  • Issue: 2
  • Year: 2014
  • Summary: In-field measurements of direct soil greenhouse gas (GHG) emissions provide critical data for quantifying the net energy efficiency and economic feasibility of crop residue-based bioenergy production systems. A major challenge to such assessments has been the paucity of field studies addressing the effects of crop residue removal and associated best practices for soil management (i.e., conservation tillage) on soil emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4). This regional survey summarizes soil GHG emissions from nine maize production systems evaluating different levels of corn stover removal under conventional or conservation tillage management across the US Corn Belt. Cumulative growing season soil emissions of CO2, N2O, and/or CH4 were measured for 2-5 years (2008-2012) at these various sites using a standardized static vented chamber technique as part of the USDA-ARS's Resilient Economic Agricultural Practices (REAP) regional partnership. Cumulative soil GHG emissions during the growing season varied widely across sites, by management, and by year. Overall, corn stover removal decreased soil total CO2 and N2O emissions by -4 and -7 %, respectively, relative to no removal. No management treatments affected soil CH4 fluxes. When aggregated to total GHG emissions (Mg CO2 eq ha(-1)) across all sites and years, corn stover removal decreased growing season soil emissions by -5 +/- 1 % (mean +/- se) and ranged from -36 % to 54 % (n = 50). Lower GHG emissions in stover removal treatments were attributed to decreased C and N inputs into soils, as well as possible microclimatic differences associated with changes in soil cover. High levels of spatial and temporal variabilities in direct GHG emissions highlighted the importance of site-specific management and environmental conditions on the dynamics of GHG emissions from agricultural soils.
  • Authors:
    • Laird, D.
    • Brown, R.
    • Hayes, D.
    • Dumortier, J.
    • Kauffman, N.
  • Source: Biomass & Bioenergy
  • Volume: 63
  • Year: 2014
  • Summary: A partial solution to problems associated with anthropogenic greenhouse gas (GHG) emissions could be the development and deployment of carbon-negative technologies, i.e., producing energy while reducing atmospheric carbon dioxide levels. Biofuels have been considered a possibility but have faced limitations due to competition with food production and GHG emissions through indirect land-use change (ILUC). In this article, we show how emissions from ILUC can potentially be reduced by producing food and bioenergy from biochar amended soils. The possibility of yield improvements from biochar would reduce the land requirement for crop production and thus, lead to a reduction in emissions from ILUC. In our application, biochar and bio-oil are produced via fast pyrolysis of corn stover. ho-oil is subsequently upgraded into a fuel suitable for use in internal combustion engines. Applying the U.S. regulatory method used to determine biofuel life cycle emissions, our results show that a biochar-induced yield improvement in the U.S. Midwest ranging from 1% to 8% above trend can lead to an ILUC credit between 1.65 and 14.79 t CO2- equivalent ha(-1) year(-1) when future emissions are assessed over the next 30 years. The model is generalizable to other feedstocks and locations and illustrates the relationship between biochar and crop production. (C) 2014 Elsevier Ltd. All rights reserved.
  • Authors:
    • Keck, P.
    • Dale, B.
    • Kim, S.
  • Source: Bioenergy Research
  • Volume: 7
  • Issue: 2
  • Year: 2014
  • Summary: This meta-study quantitatively and qualitatively compares 21 published life cycle assessment (LCA)-type studies for energy consumption and greenhouse gas (GHG) emissions of maize production in the USA. Differences between the methodologies and numerical results obtained are described. Nonrenewable energy consumption in maize production (from cradle-to-farm gate) ranges from 1.44 to 3.50 MJ/kg of maize, and GHG emissions associated with maize production range from -27 to 436 g CO2 equivalent/kg of maize. Large variations between studies exist within the input data for lime application, fuels purchased, and life cycle inventory data for fertilizer and agrochemical production. Although most studies use similar methodological approaches, major differences between studies include the following: (1) impacts associated with human labor and farm machinery production, (2) changes in carbon dioxide emissions resulting from soil organic carbon levels, and (3) indirect N2O emissions.
  • Authors:
    • Dall'erba, S.
    • Kim, T.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 183
  • Issue: January
  • Year: 2014
  • Summary: This article offers a spatio-temporal analysis of the distribution of CO2 emissions, the main cause for greenhouse gases, due to agricultural activities across US counties. Based on a novel database, we investigate how crop production output (measured in carbon) relates to CO2 emitted in the production and transportation process of the inputs needed for crop production. Various spatial statistics are used to highlight the clusters of counties with similarities in the levels and growth of output per area, input per area and productivity. At the same time, significant levels of heterogeneity are highlighted for all variables. A decomposition method allows us to uncover that the origin of interregional differences in productivity differs across the clusters of counties. Our results indicate that future mitigation policies should not fail to recognize interregional differences in the location, spatial extent and origin of carbon emissions due to the crop production process. (C) 2013 Elsevier B.V. All rights reserved.
  • Authors:
    • Zimmerman, A. R.
    • Lal, R.
    • Mukherjee, A.
  • Source: Science of The Total Environment
  • Volume: 487
  • Issue: July
  • Year: 2014
  • Summary: Short and long-term impacts of biochar on soil properties under field conditions are poorly understood. In addition, there is a lack of field reports of the impacts of biochar on soil physical properties, gaseous emissions and C stability, particularly in comparison with other amendments. Thus, three amendments - biochar produced from oak at 650°C, humic acid (HA) and water treatment residual - (WTR) were added to a scalped silty-loam soil @ 0.5% (w/w) in triplicated plots under soybean. Over the 4-month active growing season, all amendments significantly increased soil pH, but the effect of biochar was the greatest. Biochar significantly increased soil-C by 7%, increased sub-nanopore surface area by 15% and reduced soil bulk density by 13% compared to control. However, only WTR amendment significantly increased soil nanopore surface area by 23% relative to the control. While total cumulative CH4 and CO2 emissions were not significantly affected by any amendment, cumulative N2O emission was significantly decreased in the biochar-amended soil (by 92%) compared to control over the growing period. Considering both the total gas emissions and the C removed from the atmosphere as crop growth and C added to the soil, WTR and HA resulted in net soil C losses and biochar as a soil C gain. However, all amendments reduced the global warming potential (GWP) of the soil and biochar addition even produced a net negative GWP effect. The short observation period, low application rate and high intra-treatment variation resulted in fewer significant effects of the amendments on the physicochemical properties of the soils than one might expect indicating further possible experimentation altering these variables. However, there was clear evidence of amendment-soil interaction processes affecting both soil properties and gaseous emissions, particularly for biochar, that might lead to greater changes with additional field emplacement time.
  • Authors:
    • Braden, J. B.
    • Cai, X.
    • Eheart, J. W.
    • Ng, T. L.
    • Czapar, G. F.
  • Source: Journal of Water Resources Planning and Management
  • Volume: 140
  • Issue: 1
  • Year: 2014
  • Summary: Excessive nitrate loads in surface waters are a major cause of hypoxia and eutrophication. In many places, agriculture is the single largest source of nitrogen entering receiving waters. Perennial energy grass crops have the potential to reduce nitrogen loads from agricultural areas, while sequestering carbon and offering new economic opportunities for farmers. This study analyzes farm system-scale cropping and fertilizer application decisions, and resulting nitrate loads, as driven by prices for the bioenergy crop miscanthus, as well as investigates reductions of carbon and other greenhouse gas emissions and nitrogen fertilizer use. An economic model of farm-system-scale decisions is coupled to a hydrologic-agronomic model of the physical stream system to obtain nitrate loading and crop yield results for varying combinations of prices and policies for a typical Midwestern agricultural watershed. For the scenarios examined, a large reduction in stream nitrate load depends on a high price for miscanthus relative to competing crops. A price for miscanthus that exceeds 50% of the average of corn and soybean prices, per unit weight, is estimated to lead to nitrate load reductions of 25% or more. Though significant, these reductions are still less than the recommended 45% reduction in stream nitrogen flux entering the Gulf of Mexico needed to mitigate the hypoxia problem in the gulf. Miscanthus prices are unlikely ever to reach such levels. However, nitrate load reductions could still be achieved by implementing a nitrogen fertilizer reduction subsidy alongside a miscanthus market. The results also show that carbon trading is unlikely to result in any significant reduction in nitrate load. The results are useful for improving understanding of the potential of these incentives, individually and concurrently, to reduce pollution from Midwestern crop agriculture.
  • Authors:
    • Mladenoff, D. J.
    • Rothstein, D. E.
    • Forrester, J. A.
    • Palmer, M. M.
  • Source: Biomass and Bioenergy
  • Volume: 62
  • Issue: March
  • Year: 2014
  • Summary: Uncertainty exists over the magnitude of greenhouse gas (GHG) emissions associated with open land conversion to short-rotation woody biomass crops (SRWC) for bioenergy in the Northern U.S. Lake States. GHG debts incurred at the plantation establishment phase may delay the climate mitigation benefits of SRWC production. To better understand GFIG debts associated with converting open lands to SRWC, we established research plantations with willow (Salix spp), hybrid-poplar (Populus spp.), and control plots in spring 2010 at two sites in northern Michigan (ES) and Wisconsin (RH). These sites had similar climates, but differed in time since last cultivation: 5 vs. 42 years. To address the short-term effects of plantation establishment, we compared two-year biomass production and GHG emissions. We hypothesized that the long-idle ES site, with higher initial soil C and N stocks, would have higher GHG emissions following conversion compared to the recently-idle RH site, but that this would be balanced in part by greater SRWC productivity at the ES site. As hypothesized, grassland conversion resulted in two-year net GHG emissions due to land conversion of 43.21 and 33.02 Mg-CO(2)eq ha(-1) for poplar and willow at ES that was far greater than the 4.81 and 1.54 Mg-CO(2)eq ha(-1) for poplar and willow at RH. Contrary to our hypothesis, we did not observe greater SRWC productivity at ES, which will take longer than RH to reach C neutrality and begin mitigating GHG emissions. Our results show that site-specific soil and management factors determine the magnitude of GHG emissions. Published by Elsevier Ltd.
  • Authors:
    • Newman, J. A.
    • Haerri, S. A.
    • Emiljanowicz, L.
    • Ryan, G. D.
  • Source: Ecological Entomology
  • Volume: 39
  • Issue: 3
  • Year: 2014
  • Summary: 1. Elevated CO2 can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO2 and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype-specific responses to elevated CO2. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype-specific effects and possible host plant-by-insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO2 (ambient, 700, and 1000ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700ppm CO2 concentration, but increased in the 1000ppm concentration relative to ambient. The effect of CO2 on aphid density was dependent on host plant genotype; the density of aphids in high CO2 decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO2 was found, nor did we find significant genotype-by-genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO2 for some plant genotypes. The likely impact of genotype-specific responses on future changes in the genetic structure of plant and insect populations is discussed.