• Authors:
    • Caesar-Tonthat, T.
    • Stevens, W. B.
    • Sainju, U. M.
    • Liebig, M. A.
    • Wang, J.
  • Source: Journal of Environmental Quality
  • Volume: 43
  • Issue: 3
  • Year: 2014
  • Summary: Little information exists about how global warming potential (GWP) is affected by management practices in agroecosystems. We evaluated the effects of irrigation, tillage, crop rotation, and N fertilization on net GWP and greenhouse gas intensity (GHGI or GWP per unit crop yield) calculated by soil respiration (GWP R and GHGI R) and organic C (SOC) (GWP C and GHGI C) methods after accounting for CO 2 emissions from all sources (irrigation, farm operations, N fertilization, and greenhouse gas [GHG] fluxes) and sinks (crop residue and SOC) in a Lihen sandy loam from 2008 to 2011 in western North Dakota. Treatments were two irrigation practices (irrigated vs. nonirrigated) and five cropping systems (conventional-till malt barley [ Hordeum vulgaris L.] with N fertilizer [CTBN], conventional-till malt barley with no N fertilizer [CTBO], no-till malt barley-pea [ Pisum sativum L.] with N fertilizer [NTB-P], no-till malt barley with N fertilizer, and no-till malt barley with no N fertilizer [NTBO]). While CO 2 equivalents were greater with irrigation, tillage, and N fertilization than without, N 2O and CH 4 fluxes were 2 to 218 kg CO 2 eq. ha -1 greater in nonirrigated NTBN and irrigated CTBN than in other treatments. Previous year's crop residue and C sequestration rate were 202 to 9316 kg CO 2 eq. ha -1 greater in irrigated NTB-P than in other treatments. Compared with other treatments, GWP R and GWP C were 160 to 9052 kg CO 2 eq. ha -1 lower in irrigated and nonirrigated NTB-P. Similarly, GHGI R and GHGI C were lower in nonirrigated NTB-P than in other treatments. Regardless of irrigation practices, NTB-P may lower net GHG emissions more than other treatments in the northern Great Plains.
  • Authors:
    • Barsotti, J. L.
    • Sainju, U. M.
    • Wang, J.
  • Source: Soil Science Society of America Journal
  • Volume: 78
  • Issue: 1
  • Year: 2014
  • Summary: Little information is available about management practice effects on the net global warming potential (GWP) and greenhouse gas intensity (GHGI) under dryland cropping systems. We evaluated the effects of cropping sequences (conventional-tillage malt barley [Hordeum vulgaris L.]-fallow [CTB-F], no-till malt barley-pea [Pisum sativum L.] [NTB-P], and no-till continuous malt barley [NTCB]) and N fertilization rates (0 and 80 kg N ha(-1)) on net GWP and GHGI from 2008 to 2011 in eastern Montana. Carbon dioxide sources from farm operations were greater under CTB-F than NTB-P and NTCB and greater with N fertilization than without, but the sources from soil greenhouse gases (GHGs) varied among treatments and years. Carbon dioxide sinks from crop residue and soil organic C (SOC) sequestration were greater under NTB-P or NTCB with 80 kg N ha(-1) than other treatments. Net GWP and GHGI based on soil respiration (GWP(R) and GHGI(R), respectively) and SOC (GWP(C) and GHGI(C), respectively) were greater under CTB-F with 0 kg N ha(-1) than other treatments, suggesting that alternate-year fallow and the absence of N fertilization to crops can increase net GHG emissions. Because of greater grain yield but lower GWP and GHGI, NTB-P with N rates between 0 and 80 kg N ha(-1) may be used as management options to mitigate global warming potential while sustaining dryland malt barley and pea yields compared with CTB-F with 0 kg N ha(-1) in the northern Great Plains. The results can be applied to other semiarid regions with similar soil and climatic conditions.
  • Authors:
    • Liebig, M. A.
    • Caesar-TonThat, T.
    • Stevens, W. B.
    • Sainju, U. M.
    • Wang, J.
  • Source: Journal of Environmental Quality
  • Volume: 43
  • Issue: 3
  • Year: 2014
  • Summary: Little information exists about how global warming potential (GWP) is affected by management practices in agroecosystems. We evaluated the effects of irrigation, tillage, crop rotation, and N fertilization on net GWP and greenhouse gas intensity (GHGI or GWP per unit crop yield) calculated by soil respiration (GWP(R) and GHGI(R)) and organic C (SOC) (GWP(C) and GHGI(C)) methods after accounting for CO2 emissions from all sources (irrigation, farm operations, N fertilization, and greenhouse gas [GHG] fluxes) and sinks (crop residue and SOC) in a Lihen sandy loam from 2008 to 2011 in western North Dakota. Treatments were two irrigation practices (irrigated vs. nonirrigated) and five cropping systems (conventional-till malt barley [Hordeum vulgaris L.] with N fertilizer [CTBN], conventional-till malt barley with no N fertilizer [CTBO], no-till malt barley-pea [Pisum sativum L.] with N fertilizer [NTB-P], no-till malt barley with N fertilizer, and no-till malt barley with no N fertilizer [NTBO]). While CO2 equivalents were greater with irrigation, tillage, and N fertilization than without, N2O and CH4 fluxes were 2 to 218 kg CO2 eq. ha(-1) greater in nonirrigated NTBN and irrigated CTBN than in other treatments. Previous year's crop residue and C sequestration rate were 202 to 9316 kg CO2 eq. ha(-1) greater in irrigated NTB-P than in other treatments. Compared with other treatments, GWP(R) and GWP(C) were 160 to 9052 kg CO2 eq. ha(-1) lower in irrigated and nonirrigated NTB-P. Similarly, GHGI(R) and GHGI(C) were lower in nonirrigated NTB-P than in other treatments. Regardless of irrigation practices, NTB-P may lower net GHG emissions more than other treatments in the northern Great Plains.
  • Authors:
    • Jin, V. L.
    • Mitchell, R. B.
    • Follett, R. F.
    • Varvel, G. E.
    • Vogel, K. P.
    • Schmer, M. R.
  • Source: PLOS ONE
  • Volume: 9
  • Issue: 3
  • Year: 2014
  • Summary: Low-carbon biofuel sources are being developed and evaluated in the United States and Europe to partially offset petroleum transport fuels. Current and potential biofuel production systems were evaluated from a long-term continuous no-tillage corn (Zea mays L.) and switchgrass (Panicum virgatum L.) field trial under differing harvest strategies and nitrogen (N) fertilizer intensities to determine overall environmental sustainability. Corn and switchgrass grown for bioenergy resulted in near-term net greenhouse gas (GHG) reductions of -29 to -396 grams of CO2 equivalent emissions per megajoule of ethanol per year as a result of direct soil carbon sequestration and from the adoption of integrated biofuel conversion pathways. Management practices in switchgrass and corn resulted in large variation in petroleum offset potential. Switchgrass, using best management practices produced 3919 +/- 117 liters of ethanol per hectare and had 74 +/- 2.2 gigajoules of petroleum offsets per hectare which was similar to intensified corn systems (grain and 50% residue harvest under optimal N rates). Co-locating and integrating cellulosic biorefineries with existing dry mill corn grain ethanol facilities improved net energy yields (GJ ha(-1)) of corn grain ethanol by >70%. A multi-feedstock, landscape approach coupled with an integrated biorefinery would be a viable option to meet growing renewable transportation fuel demands while improving the energy efficiency of first generation biofuels.
  • Authors:
    • Lehmann, J.
    • Enders, A.
    • Whitman, T.
  • Source: Soil Biology and Biochemistry
  • Volume: 73
  • Issue: June
  • Year: 2014
  • Summary: Important due to both its role in fire-affected ecosystems, and also its proposed intentional production and application for carbon (C) management, pyrogenic organic matter (Py0M) is thought to contain very stable forms of C. However, the mechanisms behind its interactions with non-PyOM soil organic C (SOC) remain speculative, with studies often showing short-term positive and then long-term negative "priming effects" on SOC decomposition after PyOM applications. Furthermore, studies of these interactions to date have been limited to systems that do not include plants. This study describes results from a 12-week greenhouse experiment where PyOM-SOC priming effects with and without plants were investigated using stable isotope partitioning. In addition, we investigated the optimal delta C-13 proxies for sources of SOC, PyOM, and plant-derived CO2 emissions. The two-factorial experiment included the presence or absence of corn plants and of 13C-labelled PyOM. In order to control for pH and nutrient addition effects from PyOM, its pH was adjusted to that of the soil and optimal nutrient and water conditions were provided to the plants. The delta C-13 of PyOM sub-components were significantly different. Significant losses of 0.4% of the applied PyOM-C occurred in the first week. We find evidence for a "negative priming" effect of PyOM on SOC in the system (SOC losses are 48% lower with PyOM present), which occurred primarily during the first week, indicating it may be due to transient effects driven by easily mineralizable PyOM. Additionally, while the presence of corn plants resulted in significantly increased SOC losses ("positive priming"), PyOM additions counteract this effect, almost completely eliminating net C losses either by decreasing SOC decomposition or increasing corn C additions to soil. This highlights the importance of including plants in studies of PyOM-SOC interactions.
  • Authors:
    • Landis, A. E.
    • Pang, Y. L.
    • Xue, X.
  • Source: Renewable Energy
  • Volume: 66
  • Issue: June
  • Year: 2014
  • Summary: This study examines three agriculture management practices with the aim of improving the environmental performance of corn-derived products such as bioethanol. Corn production is energy intensive and contributes to water quality degradation and global warming, thus affecting the environmental impact of corn-derived ethanol. Life Cycle Assessment (LCA) is used to quantify and compare the environmental impacts of three management strategies: tillage, fertilizer choices and the use of buffer strips to sequester nutrients. Detailed energy, carbon, nitrogen and phosphorus inventories are compiled to represent corn production scenarios within the US Corn Belt. The LCA was developed using GREET 1.8 (Greenhouse Gases, Regulated Emissions, and Energy use in Transportation) and emission factors with statistical analyses to estimate energy consumption, associated air emissions, and aqueous nutrient runoff potentials. Results show that using manure fertilizers as opposed to synthetic fertilizers requires less energy, however the use of manure generates more CH4, N2O, CO2 and results in more variable concentrations of nitrogen and phosphorus leaching from farmlands. No tillage emits less greenhouse gas emissions, sequesters more soil organic carbon and slightly reduces nutrient runoff compared with conventional tillage practices. Building buffer strips of certain widths is an efficient way to reduce N and P discharge to surrounding waters with minimal effect on the energy or global warming profile. Based on the results of the LCA studies, replacing conventional tillage with no till, and installing buffer strips can improve environmental performances of corn derived ethanol. (C) 2014 Elsevier Ltd. All rights reserved.
  • Authors:
    • Karlik, J. F.
    • Angevine, W. M.
    • Brioude, J.
    • Park, J. H.
    • Weber, R.
    • Ford, T. B.
    • Fares, S.
    • Ormeno, E.
    • Gentner, D. R.
    • Goldstein, A. H.
  • Source: Atmospheric Chemistry and Physics
  • Volume: 14
  • Issue: 11
  • Year: 2014
  • Summary: Agriculture comprises a substantial, and increasing, fraction of land use in many regions of the world. Emissions from agricultural vegetation and other biogenic and anthropogenic sources react in the atmosphere to produce ozone and secondary organic aerosol, which comprises a substantial fraction of particulate matter (PM2.5). Using data from three measurement campaigns, we examine the magnitude and composition of reactive gas-phase organic carbon emissions from agricultural crops and their potential to impact regional air quality relative to anthropogenic emissions from motor vehicles in California's San Joaquin Valley, which is out of compliance with state and federal standards for tropospheric ozone PM2.5. Emission rates for a suite of terpenoid compounds were measured in a greenhouse for 25 representative crops from California in 2008. Ambient measurements of terpenoids and other biogenic compounds in the volatile and intermediate-volatility organic compound ranges were made in the urban area of Bakersfield and over an orange orchard in a rural area of the San Joaquin Valley during two 2010 seasons: summer and spring flowering. We combined measurements from the orchard site with ozone modeling methods to assess the net effect of the orange trees on regional ozone. When accounting for both emissions of reactive precursors and the deposition of ozone to the orchard, the orange trees are a net source of ozone in the springtime during flowering, and relatively neutral for most of the summer until the fall, when it becomes a sink. Flowering was a major emission event and caused a large increase in emissions including a suite of compounds that had not been measured in the atmosphere before. Such biogenic emission events need to be better parameterized in models as they have significant potential to impact regional air quality since emissions increase by several factors to over an order of magnitude. In regions like the San Joaquin Valley, the mass of biogenic emissions from agricultural crops during the summer (without flowering) and the potential ozone and secondary organic aerosol formation from these emissions are on the same order as anthropogenic emissions from motor vehicles and must be considered in air quality models and secondary pollution control strategies.
  • Authors:
    • Schauer, R. L.
    • Griffing, E. M.
    • Rice, C. W.
  • Source: Journal of Environmental Quality
  • Volume: 43
  • Issue: 2
  • Year: 2014
  • Summary: Life cycle assessment is the predominant method to compare energy and environmental impacts of agricultural production systems. In this life cycle study, we focused on the comparison of swine manure to synthetic fertilizer as nutrients for corn production in Iowa. Deep pit (DP) and anaerobic lagoon (AL) treatment systems were compared separately, and urea ammonium nitrate (UAN) was chosen as the representative synthetic fertilizer. The two functional units used were fertilization of 1000 kg of corn in a continuous corn system and fertilization of a crop yielding 1000 kg of corn and a crop yielding 298 kg of soybean in a 2-yr corn-soybean rotation. Iowa-specific versions of emission factors and energy use were used when available and compared with Intergovernmental Panel on Climate Change values. Manure was lower than synthetic fertilizer for abiotic depletion and about equal with respect to eutrophication. Synthetic fertilizer was lower than manure for global warming potential (GWP) and acidification. The choice of allocation method and life cycle boundary were important in understanding the context of these results. In the DP system, methane (CH 4) from housing was the largest contributor to the GWP, accounting for 60% of the total impact. When storage systems were compared, the DP system had 50% less GWP than the AL system. This comparison was due to reduction in CH 4 emissions from the storage system and conservation of nitrogen. Nitrous oxide emissions were the biggest contributor to the GWP of UAN fertilization and the second biggest contributor to the GWP of manure. Monte Carlo and scenario analyses were used to test the robustness of the results and sensitivity to methodology and important impact factors. The available crop-land and associated plant nutrient needs in Iowa was compared with manure production for the current hog population. On a state- or county-wide level, there was generally an excess of available land. On a farm level, there is often an excess of manure, which necessitates long-distance transport.
  • Authors:
    • Zhu, H. T.
    • Fang, X. X.
    • Pelton, M. P.
    • Blanco-Canqui, H.
    • Goddard, S.
    • Milner, M.
    • Yang, H. S.
    • Liska, A. J.
    • Suyker, A. E.
  • Source: Nature Climate Change
  • Volume: 4
  • Issue: 5
  • Year: 2014
  • Summary: Removal of corn residue for biofuels can decrease soil organic carbon (SOC; refs 1, 2) and increase CO 2 emissions because residue C in biofuels is oxidized to CO 2 at a faster rate than when added to soil. Net CO 2 emissions from residue removal are not adequately characterized in biofuel life cycle assessment (LCA; refs 6, 7, 8). Here we used a model to estimate CO 2 emissions from corn residue removal across the US Corn Belt at 580 million geospatial cells. To test the SOC model, we compared estimated daily CO 2 emissions from corn residue and soil with CO 2 emissions measured using eddy covariance, with 12% average error over nine years. The model estimated residue removal of 6 Mg per ha -1 yr -1 over five to ten years could decrease regional net SOC by an average of 0.47-0.66 Mg C ha -1 yr -1. These emissions add an average of 50-70 g CO 2 per megajoule of biofuel (range 30-90) and are insensitive to the fraction of residue removed. Unless lost C is replaced, life cycle emissions will probably exceed the US legislative mandate of 60% reduction in greenhouse gas (GHG) emissions compared with gasoline.
  • Authors:
    • Lubbers, I. M.
  • Source: Earthworms and the soil greenhouse gas balance
  • Year: 2014
  • Summary: Earthworms play an essential part in determining the greenhouse gas (GHG) balance of soils worldwide. Their activity affects both biotic and abiotic soil properties, which in turn influence soil GHG emissions, carbon (C) sequestration and plant growth. Yet, the balance of earthworms stimulating C sequestration on the one hand and increasing GHG emissions on the other has not been investigated. Indeed, much is still unclear about how earthworms interact with agricultural land use and soil management practices, making predictions on their effects in agro-ecosystems difficult. This thesis determines whether the extent of GHG mitigation by soil C sequestration as affected by earthworms is offset by earthworm-induced GHG emissions from agro-ecosystems under different types of management. To achieve this aim, mesocosm and field studies are combined, as well as meta-analytic methods to quantitatively synthesize the literature. Using meta-analysis, it is shown that, on average, earthworm activity leads to a 24% increase in aboveground biomass, a 33% increase in carbon dioxide (CO 2) emissions and a 42% increase in nitrous oxide (N 2O) emissions. The magnitude of these effects depends on soil factors (e.g., soil organic matter content), experimental factors (e.g., crop residue addition or fertilizer type and rate) and earthworm factors (e.g., earthworm ecological category and -density). Conducting both a mesocosm and a field study record that earthworm activity results in increased N 2O emissions from fertilized grasslands. Further, field conditions record an increase in earthworm-induced N 2O emissions in autumn but not in spring, suggesting that earthworm effects in the field depend on soil physicochemical parameters influenced by meteorological and seasonal dynamics. The unique two-year experiment with a simulated no-tillage (NT) system and a simulated conventional tillage (CT) system, record that earthworm presence increases GHG emissions in an NT system to the same level as in a CT system. This suggests that the GHG mitigation potential of NT agro-ecosystems is limited. When considering the C budget in the simulated NT system, it is demonstrated that over the course of the experiment earthworms increase cumulative CO 2 emissions by at least 25%, indicating a higher C loss compared to the situation without earthworms. Yet, in the presence of earthworms the incorporation of residue-derived C into all measured soil aggregate fractions also increased, indicating that earthworm activity can simultaneously enhance CO 2 emissions and C incorporation into aggregate fractions. In conclusion, the revealed dominance of GHG emissions over C sequestration as affected by earthworms implies that their presence in agro-ecosystems results in a negative impact on the soil greenhouse gas balance.