• Authors:
    • Zhang, Y.
    • Wu, L.
    • Wang, H.
    • Liu, L.
    • Huang, L.
    • Niu, Y.
    • Chai, R.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 96
  • Issue: 1
  • Year: 2013
  • Summary: Proper management of synthetic nitrogen (N) fertilizer can reduce direct N2O emission from soil and indirect CO2 emission from production and transportation of synthetic N. In the late 1990s, the average application rates of synthetic N were 212, 207 and 207 kg ha(-1), respectively, for rice, wheat, and maize in China's croplands. But research suggests that the optimal synthetic N application rates for the main grain crops in China should be in the range of 110-150 kg ha(-1). Excessive application of synthetic N has undoubtedly resulted in massive emission of greenhouse gases. Therefore, optimizing N application rates for grain crops in China has a great potential for mitigating the emission of greenhouse gases. Nevertheless, this mitigation potential (MP) has not yet been well quantified. This study aimed at estimating the MP of N2O and CO2 emissions associated with synthetic N production and transportation in China based on the provincial level statistical data. Our research indicates that the total consumption of synthetic N on grain crops in China can be reduced by 5.0-8.4 Tg yr(-1) (28-47 % of the total consumption) if the synthetic N application rate is controlled at 110-150 kg ha(-1). The estimated total MP of greenhouse gases, including direct N2O emission from croplands and indirect CO2 emission from production and transportation of synthetic N, ranges from 41.7 to 70.1 Tg CO2_eq. yr(-1). It was concluded that reducing synthetic N application rate for grain crops in China to a reasonable level of 110-150 kg ha(-1) can greatly reduce the emission of greenhouse gases, especially in the major grain-crop production provinces such as Shandong, Henan, Jiangsu, Hebei, Anhui and Liaoning.
  • Authors:
    • Pan, G.
    • Smith, P.
    • Nayak, D.
    • Zheng, J.
    • Cheng, K.
  • Source: Soil Use and Management
  • Volume: 29
  • Issue: 4
  • Year: 2013
  • Summary: To assess the topsoil carbon sequestration potential (CSP) of China's cropland, two different estimates were made: (i) a biophysical potential (BP) using a saturation limit approach based on soil organic carbon (SOC) accumulation dynamics and a storage restoration approach from the cultivation-induced SOC loss, and (ii) a technically attainable potential (TAP) with a scenario estimation approach using SOC increases under best management practices (BMPs) in agriculture. Thus, the BP is projected to be the gap in recent SOC storage to either the saturation capacity or to the SOC storage of uncultivated soil, while the TAP is the overall increase over the current SOC storage that could be achieved with the extension of BMPs. The recent mean SOC density of China's cropland was estimated to be 36.44t/ha, with a BP estimate of 2.21 Pg C by a saturation approach and 2.95 Pg C by the storage restoration method. An overall TAP of 0.62 Pg C and 0.98 Pg C was predicted for conservation tillage plus straw return and recommended fertilizer applications, respectively. This TAP is comparable to 40-60% of total CO2 emissions from Chinese energy production in 2007. Therefore, carbon sequestration in China's cropland is recommended for enhancing China's mitigation capacity for climate change. However, priority should be given to the vast dry cropland areas of China, as the CSP of China is based predominantly on the dry cropland.
  • Authors:
    • Kucharik, C. J.
    • Duran, B. E. L.
  • Source: Soil Science Society of America Journal
  • Volume: 77
  • Issue: 5
  • Year: 2013
  • Summary: Greenhouse gas emissions from soils are often measured using trace-gas flux chamber techniques without a standardized protocol, raising concerns about measurement accuracy and consistency. To address this, we compared measurements from non-steady-state non-through-flow (NTF) chambers with a non-steady-state through-flow (TF) chamber system in three bioenergy cropping systems located in Wisconsin. Additionally, we investigated the effects of the NTF flux calculation method and deployment time on flux measurements. In all cropping systems, when NTF chambers were deployed for 60 min and a linear regression (LR) flux calculation was used, soil CO2 and N2O fluxes were, on average, 18 and 12% lower, respectively, than fluxes measured with a 15-min deployment. Fluxes calculated with the HMR method, a hybrid of nonlinear and linear approaches, showed no deployment time effects for CO2 and N2O and produced 27 to 32% higher CO2 fluxes and 28 to 33% higher N2O fluxes in all crops than the LR approach with 60-min deployment. Across all crops, CO2 fluxes measured with the TF chamber system were higher by 24.4 to 84.9 mg CO2-C m(-2) h(-1) than fluxes measured with NTF chambers using either flux calculation method. These results suggest that NTF chamber deployment time should be shortened if the LR approach is used, although detection limits should be considered, and the HMR approach may be more appropriate when long deployment times are necessary. Significant differences in absolute flux values with different chamber types highlight the need for significant effort in determining the accuracy of methods or alternative flux measurement technologies.
  • Authors:
    • Borgesen, C. D.
    • Kristensen, I. T.
    • Hermansen, J. E.
    • Olesen, J. E.
    • Elsgaard, L.
  • Source: Acta Agriculturae Scandinavica, Section B — Soil & Plant Science
  • Volume: 63
  • Issue: 3
  • Year: 2013
  • Summary: Biofuels from bioenergy crops may substitute a significant part of fossil fuels in the transport sector where, e.g., the European Union has set a target of using 10% renewable energy by 2020. Savings of greenhouse gas emissions by biofuels vary according to cropping systems and are influenced by such regional factors as soil conditions, climate and input of agrochemicals. Here we analysed at a regional scale the greenhouse gas (GHG) emissions associated with cultivation of winter wheat for bioethanol and winter rapeseed for rapeseed methyl ester (RME) under Danish conditions. Emitted CO2 equivalents (CO2eq) were quantified from the footprints of CO2, CH4 and N2O associated with cultivation and the emissions were allocated between biofuel energy and co-products. Greenhouse gas emission at the national level (Denmark) was estimated to 22.1 g CO2eq MJ(1) ethanol for winter wheat and 26.0 g CO2eq MJ(1) RME for winter rapeseed. Results at the regional level (level 2 according to the Nomenclature of Territorial Units for Statistics [NUTS]) ranged from 20.0 to 23.9 g CO2eq MJ(1) ethanol and from 23.5 to 27.6 g CO2eq MJ(1) RME. Thus, at the regional level emission results varied by up to 20%. Differences in area-based emissions were only 4% reflecting the importance of regional variation in yields for the emission result. Fertilizer nitrogen production and direct emissions of soil N2O were major contributors to the final emission result and sensitivity analyses showed that the emission result depended to a large extent on the uncertainty ranges assumed for soil N2O emissions. Improvement of greenhouse gas balances could be pursued, e.g., by growing dedicated varieties for energy purposes. However, in a wider perspective, land-use change of native ecosystems to bioenergy cropping systems could compromise the CO2 savings of bioenergy production and challenge the targets set for biofuel production.
  • Authors:
    • Amiro, B. D.
    • Fraser, T. J.
  • Source: Canadian Journal of Soil Science
  • Volume: 93
  • Issue: 3
  • Year: 2013
  • Summary: Sequestering atmospheric carbon in agricultural soil is an attractive option for mitigation of rising atmospheric carbon dioxide concentrations. Perennial crops are more likely to gain carbon whereas annual crops are more likely to lose carbon. A pair of eddy covariance towers were set up near Winnipeg Manitoba, Canada, to measure the carbon dioxide flux over adjacent paired perennial grass hay fields with high soil organic carbon. A Treatment field was converted to annual cropping by spraying with herbicide, cutting and tilling. A Control field was cut, but allowed to re-grow. Differences in net ecosystem productivity between the fields were mainly caused by a loss of gross primary productivity in the Treatment field; ecosystem respiration was similar for both fields. When biomass removals and manure applications are included in the carbon budget, the Treatment field lost 149 g C M-2 whereas the Control field sequestered 96 g C m(-2), for a net difference of 245 g C M-2 over the June to December period (210 d). This suggests that perennial grass converted for annual cropping can lose more carbon than perennial grassland can sequester in a season.
  • Authors:
    • Tani, H.
    • Wang, H.
    • Li, J.
    • Wang, X.
    • Guo, M.
  • Source: International Journal of Remote Sensing
  • Volume: 34
  • Issue: 12
  • Year: 2013
  • Summary: Measurements of land-cover changes suggest that such shifts may alter atmospheric concentrations of greenhouse gases (GHGs). However, owing to the lack of large-scale GHG data, a quantitative description of the relationships between land-cover changes and GHG concentrations does not exist on a regional scale. The Greenhouse Gases Observing Satellite (GOSAT) launched by Japan on 23 January 2009 can be of use in investigating this issue. In this study, we first calculated the monthly average GHG concentrations in East Asia from April 2009 to October 2011 and found that CO2 concentration displays a seasonal cycle, but that the CH4 seasonal trend is unclear. To understand the relationship between land cover and GHG concentrations, we used GHG data from GOSAT, normalized difference vegetation index (NDVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS) and land-cover data from EAS-GlobCover (2009) to analyse the correlation coefficients between land cover and GHG concentrations. We observed that vegetation may generally be considered as a source of, but not a sink for, CO2 and CH4, either on a yearly scale or during the growing season. With respect to the relationships between land-cover types and GHG concentrations, we conclude that on a yearly scale, land-cover types are not closely correlated with GHG concentrations. During the growing season, croplands and scrublands are negatively correlated with XCO2 (the ratio of the total number of CO2 molecules to that of dry air molecules), and forest, grasslands and bare areas are positively correlated with XCO2. Forest and croplands can be viewed as CH4 sources, while scrublands and grasslands can be thought of as CH4 sinks.
  • Authors:
    • Lafond, G. P.
    • Schoenau, J. J.
    • Hangs, R. D.
  • Source: Journal of Plant Nutrition and Soil Science
  • Volume: 176
  • Issue: 2
  • Year: 2013
  • Summary: With a world population now > 7 billion, it is imperative to conserve the arable land base, which is increasingly being leveraged by global demands for producing food, feed, fiber, fuel, and facilities (i.e., infra-structure needs). The objective of this study was to determine the effect of varying fertilizer-N rates on soil N availability, mineralization, and CO2 and N2O emissions of soils collected at adjacent locations with contrasting management histories: native prairie, short-term (10 y), and long-term (32 y) no-till continuous-cropping systems receiving five fertilizer-N rates (0, 30, 60, 90, and 120kg N ha1) for the previous 9 y on the same plots. Intact soil cores were collected from each site after snowmelt, maintained at field capacity, and incubated at 20 degrees C for 6 weeks. Weekly assessments of soil nutrient availability along with CO2 and N2O emissions were completed. There was no difference in cumulative soil N supply between the unfertilized long-term no-till and native prairie soils, while annual fertilizer-N additions of 120kg N ha1 were required to restore the N-supplying power of the short-term no-till soil to that of the undisturbed native prairie soil. The estimated cumulative CO2-C and N2O-N emissions among soils ranged from 231.8474.7 g m2 to 183.9862.5 mg m2, respectively. Highest CO2 fluxes from the native prairie soil are consistent with its high organic matter content, elevated microbial activity, and contributions from root respiration. Repeated applications of 60kg N ha1 resulted in greater residual inorganic-N levels in the long-term no-till soil, which supported larger N2O fluxes compared to the unfertilized control. The native prairie soil N2O emissions were equal to those from both short- and long-term no-till soils receiving repeated fertilizer-N applications at typical agronomic rates (e.g., 90kg N ha1). Eighty-eight percent of the native soil N2O flux was emitted during the first 2 weeks and is probably characteristic of rapid denitrification rates during the dormant vegetative period after snowmelt within temperate native grasslands. There was a strong correlation (R-2 0.64; p < 0.03) between measured soil Fe-supply rate and N2O flux, presumably due to anoxic microsites within soil aggregates resulting from increased microbial activity. The use of modern no-till continuous diversified cropping systems, along with application of fertilizer N, enhances the soil N-supplying power over the long-term through the build-up of mineralizable N and appears to be an effective management strategy for improving degraded soils, thus enhancing the productive capacity of agricultural ecosystems. However, accounting for N2O emissions concomitant with repeated fertilizer-N applications is imperative for properly assessing the net global warming potential of any land-management system.
  • Authors:
    • Prochnow, A.
    • Meyer-Aurich, A.
    • Hansen, A.
  • Source: Biomass and Bioenergy
  • Volume: 56
  • Year: 2013
  • Summary: This study investigates the variance of the overall greenhouse gas mitigation potential of a complete second generation stationary bio-electricity production system, generated by poplar wood chips (Populus spec.) in Germany, using Monte Carlo simulations. We computed the GHG emissions as E-B = (-0.034 +/- 0.021) kg CO2e MJ(-1) (mean +/- SD) and the mitigation factor as MFB = (0.274 +/- 0.021) kg CO2e MJ(-1) following a life cycle assessment-based approach. Additionally, avoided nitrous oxide (N2O) emissions due to land use change were considered in the assessment. The most important factor for the overall mitigation variability was the uncertainty of the organic carbon changes in the soil, followed by the variability of yields. The uncertainty of (i) direct N2O emissions from the poplar site or (ii) the reference rye site as well as (iii) the uncertainty of heat recovery percentage was of minor importance. Uncertainties in the global warming potentials of nitrous oxide and methane and in the transport distance were found to be irrelevant. The uncertainty of the GHG mitigation which was associated with this specific electricity generation by poplar wood chips gasification was significantly lower compared to the variability of another common bio-electricity system (biogas). Uncertainty implications seem to be system-specific and therefore should be analysed separately for each bioenergy pathway under consideration. (C) 2013 Elsevier Ltd. All rights reserved.
  • Authors:
    • Ragsdale, D. W.
    • Hill, J. D.
    • Yang, Y.
    • Heimpel, G. E.
  • Source: PLOS ONE
  • Volume: 8
  • Issue: 8
  • Year: 2013
  • Summary: Greenhouse gas emissions associated with pesticide applications against invasive species constitute an environmental cost of species invasions that has remained largely unrecognized. Here we calculate greenhouse gas emissions associated with the invasion of an agricultural pest from Asia to North America. The soybean aphid, Aphis glycines, was first discovered in North America in 2000, and has led to a substantial increase in insecticide use in soybeans. We estimate that the manufacture, transport, and application of insecticides against soybean aphid results in approximately 10.6 kg of carbon dioxide (CO2) equivalent greenhouse gasses being emitted per hectare of soybeans treated. Given the acreage sprayed, this has led to annual emissions of between 6 and 40 million kg of CO2 equivalent greenhouse gasses in the United States since the invasion of soybean aphid, depending on pest population size. Emissions would be higher were it not for the development of a threshold aphid density below which farmers are advised not to spray. Without a threshold, farmers tend to spray preemptively and the threshold allows farmers to take advantage of naturally occurring biological control of the soybean aphid, which can be substantial. We find that adoption of the soybean aphid economic threshold can lead to emission reductions of approximately 300 million kg of CO2 equivalent greenhouse gases per year in the United States. Previous studies have documented that biological control agents such as lady beetles are capable of suppressing aphid densities below this threshold in over half of the soybean acreage in the U.S. Given the acreages involved this suggests that biological control results in annual emission reductions of over 200 million kg of CO2 equivalents. These analyses show how interactions between invasive species and organisms that suppress them can interact to affect greenhouse gas emissions.
  • Authors:
    • Hao, X. M.
    • Thelen, K. D.
    • Gao, J.
  • Source: Agronomy Journal
  • Volume: 105
  • Issue: 3
  • Year: 2013
  • Summary: Corn ( Zea mays L.) and corn stover are currently considered the most abundant and readily accessible feedstock resources for renewable bioethanol. Whole-plant corn harvest could increase bioethanol yield compared with a conventional separated grain and stover harvest. There is limited research, however, on the environmental effects of whole-plant harvest strategies, including nonrenewable energy efficiency, greenhouse gas (GHG) emission intensity, and soil organic C (SOC) changes. In this study, harvest methods together with bioprocessing steps were combined through life cycle analysis (LCA) models, and SOC changes for corn farming with different harvest methods were simulated by a Daycent ecosystem model. The harvest data were from four agronomy farms (Branch, Ingham, Huron, and Menominee) of Michigan State University across south to north in Michigan. The LCA results showed that a whole-plant harvest strategy could increase energy efficiency 3.4 to 4.3 times and reduce GHG emissions by 382% relative to a traditional separate grain and stover harvest strategy. The analyses also indicated, however, that whole-plant harvest could reduce SOC (66.922.9 g CO 2 equivalent m -2) annually during 50 yr of continuous corn farming at Branch, Ingham, and Huron, while the conventional harvest system could sequestrate CO 2 into SOC at Ingham, Huron, and Menominee. The Daycent simulation also showed that a winter cover crop planted after whole-plant immature corn harvest could compensate for part of the SOC loss associated with a whole-corn-plant harvest.