• 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:
    • Ruser, R.
    • Stolze, M.
    • Fliessbach, A.
    • Maeder, P.
    • Muller, A.
    • Gattinger, A.
    • Skinner, C.
    • Niggli, U.
  • Source: Science of The Total Environment
  • Volume: 468-469
  • Issue: January
  • Year: 2014
  • Summary: It is anticipated that organic farming systems provide benefits concerning soil conservation and climate protection. A literature search on measured soil-derived greenhouse gas (GHG) (nitrous oxide and methane) fluxes under organic and non-organic management from farming system comparisons was conducted and followed by a meta-analysis. Up to date only 19 studies based on field measurements could be retrieved. Based on 12 studies that cover annual measurements, it appeared with a high significance that area-scaled nitrous oxide emissions from organically managed soils are 492 +/- 160 kg CO2 eq. ha(-1) a(-1) lower than from non-organically managed soils. For arable soils the difference amounts to 497 +/- 162 kg CO2 eq. ha(-1) a(-1). However, yield-scaled nitrous oxide emissions are higher by 41 +/- 34 kg CO2 eq. t(-1) DM under organic management (arable and use). To equalize this mean difference in yield-scaled nitrous oxide emissions between both farming systems, the yield gap has to be less than 17%. Emissions from conventionally managed soils seemed to be influenced mainly by total N inputs, whereas for organically managed soils other variables such as soil characteristics seemed to be more important. This can be explained by the higher bioavailability of the synthetic N fertilisers in non-organic farming systems while the necessary mineralisation of the N sources under organic management leads to lower and retarded availability. Furthermore, a higher methane uptake of 3.2 +/- 2.5 kg CO2 eq. ha(-1) a(-1) for arable soils under organic management can be observed. Only one comparative study on rice paddies has been published up to date. All 19 retrieved studies were conducted in the Northern hemisphere under temperate climate. Further GHG flux measurements in farming system comparisons are required to confirm the results and close the existing knowledge gaps. (C) 2013 Elsevier B.V. All rights reserved.
  • 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:
    • Liu, H.-Y.
    • Qiu, J.-J.
    • Li, H.
    • Wang, L.-G.
    • Yang, L.
  • Source: Journal of Integrative Agriculture
  • Volume: 13
  • Issue: 4
  • Year: 2014
  • Summary: Spring maize is one of the most popular crops planted in northeastern China. The cropping systems involving spring maize have been maintaining high production through intensive management practices. However, the high rates of nitrogen (N) fertilizers application could have introduced a great amount of nitrous oxide (N2O) into the atmosphere. It is crucial for sustaining the maize production systems to reduce N2O emissions meanwhile maintaining the optimum yields by adopting alternative farming management practices. The goal of this study was to evaluate effects of alternative fertilization and crop residue management practices on N2O emission as well as crop yield for a typical maize field in northeastern China. Field experiments were conducted during the 2010-2011 maize growing seasons (from early May to late September) in Liaoning Province, northeastern China. N2O fluxes were measured at the field plots with six different treatments including no N fertilizer use (CK), farmers' conventional N fertilizer application rate (FP), reduced N fertilizer rate (OPT), reduced N fertilizer rate combined with crop straw amendment (OPTS), slow-release N fertilizer (CRF), and reduced N fertilizer rate combined with nitrification inhibitor (OPT+DCD). The static chamber method combined with gas chromatography technique was employed to conduct the measurements of N2O fluxes. The field data showed that N2O emissions varied across the treatments. During the maize growing season in 2010, the total N2O emissions under the treatments of CK, FP, OPT, OPTS, and CRF were 0.63, 1.11, 1.03, 1.26, and 0.98 kg N ha(-1), respectively. The seasonal cumulative N2O emissions were 0.54, 1.07, 0.96, 1.12, and 0.84 kg N ha(-1), respectively, under CK, FP, OPT, OPTS, and OPT+DCD in 2011. In comparison with FP, CRF or OPT+DCD reduced the N2O emissions by 12 or 21%, respectively, while the crop yields remained unchanged. The results indicate that the reduction of N-fertilizer application rate in combination with the slow-release fertilizer type or nitrification inhibitor could effectively mitigate N2O emissions from the tested field. The incorporation of crop residue didn't show positive effect on mitigating N2O emissions from the tested cropping system. The field study can provide useful information for the on-going debate on alternative N fertilization strategies and crop straw management in China. However, further studies would be needed to explore the long-term impacts of the alternative management practices on a wide range of environmental services.
  • 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:
    • Rothstein, D. E.
    • Forrester, J. A.
    • Palmer, M. M.
    • Mladenoff, D. J.
  • Source: GCB Bioenergy
  • Volume: 6
  • Issue: 4
  • Year: 2014
  • Summary: Short-rotation woody biomass crops (SRWC) have been proposed as a major feedstock source for bioenergy generation in the Northeastern US. To quantify the environmental effects and greenhouse gas (GHG) balance of crops including SRWC, investigators need spatially explicit data which encompass entire plantation cycles. A knowledge gap exists for the establishment period which makes current GHG calculations incomplete. In this study, we investigated the effects of converting pasture and hayfields to willow ( Salix spp.) and hybrid-poplar ( Populus spp.) SRWC plantations on soil nitrogen (N) cycling, nitrous oxide (N 2O) emissions, and nitrate (NO 3-) leaching at six sites of varying soil and climate conditions across northern Michigan and Wisconsin, following these plantations from pre conversion through their first 2 years. All six sites responded to establishment with increased N 2O emissions, available inorganic N, and, where it was measured, NO 3- leaching; however, the magnitude of these impacts varied dramatically among sites. Soil NO 3- levels varied threefold among sites, with peak extractable NO 3- concentrations ranging from 15 to 49 g N kg -1 soil. Leaching losses were significant and persisted through the second year, with 44-112 kg N ha -1 leached in SRWC plots. N 2O emissions in the first growing season varied 30-fold among sites, from 0.5 to 17.0 Mg-CO 2eq ha -1 (carbon dioxide equivalents). N 2O emissions over 2 years resulted in N 2O emissions due to plantation establishment that ranged from 0.60 to 22.14 Mg-CO 2eq ha -1 above baseline control levels across sites. The large N losses we document herein demonstrate the importance of including direct effects of land conversion in life-cycle analysis (LCA) studies of SRWC GHG balance. Our results also demonstrate the need for better estimation of spatial variability of N cycling processes to quantify the full environmental impacts of SRWC plantations.
  • Authors:
    • Asam, Z.-u.-Z.
    • Zhang, W.
    • Li, D.
    • Xu, X.
    • Luo, Y.
    • Kumar, S.
    • Rafique, R.
  • Source: Global and Planetary Change
  • Volume: 118
  • Issue: July
  • Year: 2014
  • Summary: Greenhouse gas (GHG) emissions play an important role in regulating the Earth surface temperature. GHG emissions from soils are sensitive to climate change and land management practices. According to general circulation model (GCM) predictions, the Earth will experience a combination of increased temperature and altered precipitation regimes which may result in an increase or a decrease of GHG exchange. The effect of climate change on GHG emissions can be examined through both experiments and by applying process-based models, which have become more popular. The performance of those models can be improved significantly by appropriate calibration procedures. The objectives of this study are to: (i) calibrate the DAYCENT model using advance parameter estimation (PEST) software and to (ii) examine simulated GHG dynamics at daily and seasonal time-scales under a climate change scenario of increased temperature (2 degrees C) and a precipitation regime change where 40% of precipitation during the dry season was redistributed to the wet season. The algorithmic calibration improved the model performance by reducing the sum of weighted squared residual differences by up to 223% (decreased from 1635 to 505 g N2O-N ha(-1) d(-1)) for N2O and 22% (decreased from 623 to 507% WFPS) for water filled pore space (WFPS) simulation results. In the altered climate scenario, total N2O and CO2 fluxes decreased by 9% (from 231 to 2.10 kg N2O-N ha(-1) yr(-1)) and 38% (from 1134.08 to 699.56 kg CO2 ha-1 yr-1) respectively, whereas CH4 fluxes increased by 10% (from 1.62 to 1.80 kg CH4 ha-1 yr-1). Our results show a larger impact of altered climate on CO2 as compared to N2O and CH4 emissions. The main difference in all GHG emissions was observed in summer period due to drought conditions created by reduced precipitation and increased temperatures. However, the GHG dynamics can also be attributed to no-till practices which play an important role in changing the soil moisture conditions for aerobic and anaerobic microsites. These results are based on a process-based model, therefore, we suggest performing experimental studies to examine the GHG emissions under increased temperature and especially under altered precipitation regimes. (C) 2014 Elsevier B.V. All rights reserved.
  • Authors:
    • Lu, S.
    • Zhang, F.
    • Chen, Q.
    • Wang, J.
    • Ren, T.
  • Source: PLoS ONE
  • Volume: 9
  • Issue: 5
  • Year: 2014
  • Summary: With the goal of improving N fertilizer management to maximize soil organic carbon (SOC) storage and minimize N losses in high-intensity cropping system, a 6-years greenhouse vegetable experiment was conducted from 2004 to 2010 in Shouguang, northern China. Treatment tested the effects of organic manure and N fertilizer on SOC, total N (TN) pool and annual apparent N losses. The results demonstrated that SOC and TN concentrations in the 0-10cm soil layer decreased significantly without organic manure and mineral N applications, primarily because of the decomposition of stable C. Increasing C inputs through wheat straw and chicken manure incorporation couldn't increase SOC pools over the 4 year duration of the experiment. In contrast to the organic manure treatment, the SOC and TN pools were not increased with the combination of organic manure and N fertilizer. However, the soil labile carbon fractions increased significantly when both chicken manure and N fertilizer were applied together. Additionally, lower optimized N fertilizer inputs did not decrease SOC and TN accumulation compared with conventional N applications. Despite the annual apparent N losses for the optimized N treatment were significantly lower than that for the conventional N treatment, the unchanged SOC over the past 6 years might limit N storage in the soil and more surplus N were lost to the environment. Consequently, optimized N fertilizer inputs according to root-zone N management did not influence the accumulation of SOC and TN in soil; but beneficial in reducing apparent N losses. N fertilizer management in a greenhouse cropping system should not only identify how to reduce N fertilizer input but should also be more attentive to improving soil fertility with better management of organic manure.
  • Authors:
    • Malins, C. J.
    • Searle, S. Y.
  • Source: Biomass and Bioenergy
  • Volume: 65
  • Issue: June
  • Year: 2014
  • Summary: Expectations are high for energy crops. Government policies in the United States and Europe are increasingly supporting biofuel and heat and power from cellulose, and biomass is touted as a partial solution to energy security and greenhouse gas mitigation. Here, we review the literature for yields of 5 major potential energy crops: Miscanthus spp., Panicum virgatum (switch grass), Populus spp. (poplar), Salix spp. (willow), and Eucalyptus spp. Very high yields have been achieved for each of these types of energy crops, up to 40 t ha(-1) y(-1) in small, intensively managed trials. But yields are significantly lower in semi-commercial scale trials, due to biomass losses with drying, harvesting inefficiency under real world conditions, and edge effects in small plots. To avoid competition with food, energy crops should be grown on non-agricultural land, which also lowers yields. While there is potential for yield improvement for each of these crops through further research and breeding programs, for several reasons the rate of yield increase is likely to be slower than historically has been achieved for cereals; these include relatively low investment, long breeding periods, low yield response of perennial grasses to fertilizer, and inapplicability of manipulating the harvest index. Miscanthus x giganteus faces particular challenges as it is a sterile hybrid. Moderate and realistic expectations for the current and future performance of energy crops are vital to understanding the likely cost and the potential of large-scale production. (c) 2014 Elsevier Ltd. All rights reserved.