• Authors:
    • Schmidt, J. E.
    • Thomsen, S. T.
    • Jensen, M.
    • Heiske, S.
    • Hauggaard-Nielsen, H.
    • Carter, M. S.
    • Johansen, A.
    • Ambus, P.
  • Source: GCB Bioenergy
  • Volume: 4
  • Issue: 4
  • Year: 2012
  • Summary: One way of reducing the emissions of fossil fuel-derived carbon dioxide (CO2) is to replace fossil fuels with biofuels produced from agricultural biomasses or residuals. However, cultivation of soils results in emission of other greenhouse gases (GHGs), especially nitrous oxide (N2O). Previous studies on biofuel production systems showed that emissions of N2O may counterbalance a substantial part of the global warming reduction, which is achieved by fossil fuel displacement. In this study, we related measured field emissions of N2O to the reduction in fossil fuel-derived CO2, which was obtained when agricultural biomasses were used for biofuel production. The analysis included five organically managed feedstocks (viz. dried straw of sole cropped rye, sole cropped vetch and intercropped ryevetch, as well as fresh grassclover and whole crop maize) and three scenarios for conversion of biomass into biofuel. The scenarios were (i) bioethanol, (ii) biogas and (iii) coproduction of bioethanol and biogas. In the last scenario, the biomass was first used for bioethanol fermentation and subsequently the effluent from this process was utilized for biogas production. The net GHG reduction was calculated as the avoided fossil fuel-derived CO2, where the N2O emission was subtracted. This value did not account for fossil fuel-derived CO2 emissions from farm machinery and during conversion processes that turn biomass into biofuel. The greatest net GHG reduction, corresponding to 700800 g CO2 m(-2), was obtained by biogas production or coproduction of bioethanol and biogas on either fresh grassclover or whole crop maize. In contrast, biofuel production based on lignocellulosic crop residues (i.e. rye and vetch straw) provided considerably lower net GHG reductions (=215 g CO2 m(-2)), and even negative numbers sometimes. No GHG benefit was achieved by fertilizing the maize crop because the extra crop yield, and thereby increased biofuel production, was offset by enhanced N2O emissions.
  • Authors:
    • Leytem, A. B.
    • Venterea, R. T.
    • Fixen, P. E.
    • Snyder, C. S.
    • Liebig, M. A.
    • Del Grosso, S. J.
    • Cavigelli, M. A.
    • McLain, J. E.
    • Watts, D. B.
  • Source: Frontiers in Ecology and the Environment
  • Volume: 10
  • Issue: 10
  • Year: 2012
  • Summary: The use of commercial nitrogen (N) fertilizers has led to enormous increases in US agricultural productivity. However, N losses from agricultural systems have resulted in numerous deleterious environmental impacts, including a continuing increase in atmospheric nitrous oxide (N2O), a greenhouse gas (GHG) and an important catalyst of stratospheric ozone depletion. Although associated with about 7% of total US GHG emissions, agricultural systems account for 75% of total US N2O emissions. Increased productivity in the crop and livestock sectors during the past 30 to 70 years has resulted in decreased N2O emissions per unit of production, but N2O emissions from US agriculture continue to increase at a rate of approximately 0.46 teragrams of carbon dioxide equivalents per year (2002-2009). This rate is lower than that during the late 20th century. Improvements in agricultural productivity alone may be insufficient to lead to reduced emissions; implementing strategies specifically targeted at reducing N2O emissions may therefore be necessary. Front Ecol Environ 2012; 10(10): 537-546, doi:10.1890/120054
  • Authors:
    • Chidthaisong, A.
    • Lu, Y.
    • Yuan, Q.
    • Klose, M.
    • Conrad, R.
  • Source: Soil Biology and Biochemistry
  • Volume: 49
  • Issue: June
  • Year: 2012
  • Summary: Straw amendment is a common practice for improving the fertility of rice field soils, but it also enhances production of the greenhouse gas methane. To quantify carbon flux partitioning and priming effects due to straw amendment, we measured delta C-13 in CH4 and CH4 precursors produced in anoxic slurries of soil from Italy, China and Thailand after addition of straw from either rice (C3 plant) or maize plants (C4 plant), which have different delta C-13 signatures. The delta C-13 values of the CH4, acetate and CO2 produced were similar when expressed as the difference to the delta C-13 value of the straw applied. These results indicated that the C-13-isotopic fractionation involved in methanogenic decomposition was similar for rice straw and maize straw. However, measurement of CH4 produced in soil without or with straw showed that isotopic fractionation during methanogenic degradation of straw was smaller than during degradation of soil organic matter. Isotopic fractionation during hydrogenotrophic methanogenesis, measured in the presence of methyl fluoride, with straw was also smaller than with soil organic matter. The results show that C-13-isotopic analysis after application of rice straw and maize straw is a convenient approach for quantifying carbon flux partitioning during methanogenic degradation of straw and soil organic matter. In our experiments, straw degradation accounted for most of the CH4 production and caused a negative priming effect on the methanogenic degradation of soil organic matter. (c) 2012 Elsevier Ltd. All rights reserved.
  • Authors:
    • Decock, C.
    • Leakey, A. D. B.
    • Gray, S. B.
    • Venterea, R.
    • Chung, H.
    • Six, J.
  • Source: Soil Biology and Biochemistry
  • Volume: 51
  • Issue: August
  • Year: 2012
  • Summary: In order to predict and mitigate future climate change, it is essential to understand plant-mediated effects of elevated CO2 (eCO(2)) and O-3 (eO(3)) on N-cycling, including N2O emissions. This is of particular interest for agroecosystems. since N-cycling and N2O emissions are responsive to adaptive management. We investigated the interaction of soil moisture content with eCO(2) and eO(3) on potential N2O emissions from SoyFACE during a 28-day laboratory incubation experiment. We also assessed field N2O fluxes during 2 soybean-growing seasons. In addition, we sought to link previously observed changes in soybean growth and production to belowground processes over a longer time scale by analyzing changes in natural abundance stable isotope ratios of soil N (delta N-15). This method relies on the concept that soil delta N-15 can only change when inputs or outputs with an isotope signature different from that of soil N are altered. We found no major effects of eCO(2) and eO(3) on laboratory and field measured N2O emissions. Natural abundance isotope analyses suggested, however, a decrease in belowground allocation of biologically fixed N in combination with decreased total gaseous N loss by eCO(2), resulting in a tighter N cycle in the longer-term. In contrast, the isotope data suggested an increase in belowground allocation of biologically fixed N under eO(3), leading to increased gaseous N loss, most likely in the form of N-2. Given that effects of eCO(2) and eO(3) on N pools and instantaneous transformation rates in surface soil layers of this agroecosystem have been minimal, our results illustrate the importance of evaluating longer-term changes in N turnover rates. We conclude that eCO(2) decelerates whereas eO(3) accelerates N-cycling in the longer-term, but feedback through changed N2O emissions is not occurring in this soybean system. (C) 2012 Elsevier Ltd. All rights reserved.
  • Authors:
    • Vasquez-Murrieta, S.
    • Gutierrez-Miceli, F. A.
    • Montes-Molina, J.
    • Marsch, R.
    • Luna-Guido, M.
    • Verhulst, N.
    • Ramirez-Villanueva, D. A.
    • Patino-Zuniga, L.
    • Gutierrez-Oliva, V. F.
    • Dendooven, L.
    • Govaerts, B.
  • Source: Science of The Total Environment
  • Volume: 431
  • Issue: August
  • Year: 2012
  • Summary: In 1991, the 'International Maize and Wheat Improvement Center' (CIMMYT) started a field experiment in the rain fed Mexican highlands to investigate conservation agriculture (CA) as a sustainable alternative for conventional maize production practices (CT). CT techniques, characterized by deep tillage, monoculture and crop residue removal, have deteriorated soil fertility and reduced yields. CA, which combines minimum tillage, crop rotations and residue retention, restores soil fertility and increases yields. Soil organic matter increases in CA compared to CT, but increases in greenhouse gas emissions (GHG) in CA might offset the gains obtained to mitigate global warming. Therefore, CO2, CH4 and N2O emissions, soil temperature, C and water content were monitored in CA and CT treatments in 2010-2011. The cumulative GHG emitted were similar for CA and CT in both years, but the C content in the 0-60 cm layer was higher in CA (117.7 Mg C ha(-1)) than in CT (69.7 Mg C ha(-1)). The net global warming potential (GWP) of CA (considering soil C sequestration, GHG emissions, fuel use, and fertilizer and seeds production) was -7729 kg CO2 ha(-1) y(-1) in 2008-2009 and -7892 kg CO2 ha(-1) y(-1) in 2010-2011, whereas that of CT was 1327 and 1156 kg CO2 ha(-1) y(-1). It was found that the contribution of CA to GWP was small compared to that of CT. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Marsch, R.
    • Luna-Guido, M.
    • Verhulst, N.
    • Patino-Zuniga, L.
    • Dendooven, L.
    • Govaerts, B.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 152
  • Issue: May
  • Year: 2012
  • Summary: Conservation agriculture based on (1) minimal soil movement, (2) retention of rational amounts of crop residue, (3) economically viable crop rotations restores soil fertility. Conservation agriculture improves soil characteristics, but it remains to be seen how zero tillage (ZT) affected greenhouse gas emissions (GHG) and the global warming potential (GWP) compared to conventional tillage (Cr) when crop residue was kept or removed in a maize-wheat crop rotation since 1991. The soil organic C content in the 0-60 cm layer was larger in ZT (117.7 Mg C ha(-1)) compared to CT (76.8 Mg C ha(-1)) when residue was retained, but similar when it was removed. Tillage and residue management had only a small effect on GWP of the GHG emissions. However, the C sequestered in the 0-60cm was affected by tillage and crop residue management, resulting in a negative net GWP for ZT with crop residue retention (-6.277 Mg CO2 ha(-1) y(-1)) whereas in the other management practices it ranged from 1.288 to 1.885 Mg CO2 ha(-1) y(-1). It was found that cultivation technique had little effect on the GWP of the GHG, but had a large effect on C sequestered in the 0-60cm layer and the net GWP. (C) 2012 Elsevier B.V. All rights reserved.
  • Authors:
    • Zegada-Lizarazu, W.
    • Walter, K.
    • Valentine, J.
    • Djomo, S. Njakou
    • Monti, A.
    • Mander, U.
    • Lanigan, G. J.
    • Jones, M. B.
    • Hyvonen, N.
    • Freibauer, A.
    • Flessa, H.
    • Drewer, J.
    • Carter, M. S.
    • Skiba, U.
    • Hastings, A.
    • Osborne, B.
    • Don, A.
    • Zenone, T.
  • Source: GCB Bioenergy
  • Volume: 4
  • Issue: 4
  • Year: 2012
  • Summary: Bioenergy from crops is expected to make a considerable contribution to climate change mitigation. However, bioenergy is not necessarily carbon neutral because emissions of CO2, N2O and CH4 during crop production may reduce or completely counterbalance CO2 savings of the substituted fossil fuels. These greenhouse gases (GHGs) need to be included into the carbon footprint calculation of different bioenergy crops under a range of soil conditions and management practices. This review compiles existing knowledge on agronomic and environmental constraints and GHG balances of the major European bioenergy crops, although it focuses on dedicated perennial crops such as Miscanthus and short rotation coppice species. Such second-generation crops account for only 3% of the current European bioenergy production, but field data suggest they emit 40% to >99% less N2O than conventional annual crops. This is a result of lower fertilizer requirements as well as a higher N-use efficiency, due to effective N-recycling. Perennial energy crops have the potential to sequester additional carbon in soil biomass if established on former cropland (0.44 Mg soil C ha(-1) yr(-1) for poplar and willow and 0.66 Mg soil C ha(-1) yr(-1) for Miscanthus). However, there was no positive or even negative effects on the C balance if energy crops are established on former grassland. Increased bioenergy production may also result in direct and indirect land-use changes with potential high C losses when native vegetation is converted to annual crops. Although dedicated perennial energy crops have a high potential to improve the GHG balance of bioenergy production, several agronomic and economic constraints still have to be overcome.
  • Authors:
    • Dyer,Lisa
    • Oelbermann,Maren
    • Echarte,Laura
  • Source: Journal of Plant Nutrition and Soil Science
  • Volume: 175
  • Issue: 3
  • Year: 2012
  • Summary: The Argentine Pampa is one of the major global regions for the production of maize (Zea mays L.) and soybean (Glycine max L. [Merr.]), but intense management practices have led to soil degradation and amplified greenhouse-gas (GHG) emissions. This paper presents preliminary data on the effect of maize-soybean intercrops compared with maize and soybean sole crops on the short-term emission rates of CO2 and N2O and its relationship to soil moisture or temperature over two field seasons. Soil organic carbon (SOC) concentrations were significantly greater (p < 0.05) in the maize sole crop and intercrops, whereas soil bulk density was significantly lower in the intercrops. Soil CO2 emission rates were significantly greater in the maize sole crop but did not differ significantly for N2O emissions. Over two field seasons, both trace gases showed a general trend of greater emission rates in the maize sole crop followed by the soybean sole crop and were lowest in the intercrops. Linear regression between soil GHG (CO2 and N2O) emission rates and soil temperature or volumetric soil moisture were not significant except in the 1:2 intercrop where a significant relationship was observed between N2O emissions and soil temperature in the first field season and between N2O and volumetric soil moisture in the second field season. Our results demonstrated that intercropping in the Argentine Pampa may be a more sustainable agroecosystem land-management practice with respect to GHG emissions.
  • Authors:
    • Olander, L. P.
    • Eagle, A. J.
  • Source: Advances in Agronomy
  • Volume: 115
  • Year: 2012
  • Summary: Responsible for 6% of U.S. greenhouse gas (GHG) production, agricultural land use has significant potential to reduce these emissions and capture additional carbon in the soil. Many different activities have been proposed for such mitigation, but assessments of the biophysical potential have been limited and have not provided direct comparison among the many options. We present an in-depth review of the scientific literature, with a side-by-side comparison of net biophysical GHG mitigation potential for 42 different agricultural land management activities in the United States, many of which are likely applicable in other regions. Twenty of these activities are likely to be beneficial for GHG mitigation and have sufficient research to support this conclusion. Limited research leads to uncertainty for 15 other activities that may have positive mitigation potential, and the remaining activities have small or negative GHG mitigation potential or life-cycle GHG concerns. While we have sufficient information to move forward in implementing a number of activities, there are some high-priority research needs that will help clarify problematic uncertainties.
  • Authors:
    • Griffis, T. J.
    • Fassbinder, J. J.
    • Baker, J. M.
  • Source: Agricultural and Forest Meteorology
  • Volume: 153
  • Issue: February
  • Year: 2012
  • Summary: Separation of the photosynthetic (F-P) and respiratory (F-R) fluxes of net CO2 exchange (F-N) remains a necessary step toward understanding the biological and physical controls on carbon cycling between the soil, biomass, and atmosphere. Despite recent advancements in stable carbon isotope partitioning methodology, several potential limitations can cause uncertainty in the partitioned results. Here, we combined an automated chamber system with a tunable diode laser (TDL) to evaluate carbon isotope partitioning under controlled environmental conditions. Experiments were conducted in a climate controlled greenhouse utilizing both soybean (C-3 pathway) and corn (C-4 pathway) treatments. Under these conditions, net exchange of (CO2)-C-13 and (CO2)-C-12 was obtained with an improved signal to noise ratio. Further, the chamber system was used to estimate soil evaporation (E) and plant transpiration (T), allowing for an improved estimate of the total conductance to CO2 (g(c)). This study found that the incorporation of short-term and diel variability in the isotope composition of respiration (delta(R)) caused F-P to nearly double in the corn system while only slightly increasing in the soybean system. Variability in both g(c) and the CO2 bundle sheath leakage factor for C-4 plants (phi) also had a significant influence on F-P. In addition, chamber measurements of F-N and its isotope composition (delta(N)) indicated that post-illumination processes caused a decrease in plant respiration for up to 3 h following light termination. Finally, this study found systematic differences between the isotope and temperature-regression partitioning methods on the diel time scale. Published by Elsevier B.V.