N2O Release from agro-biofuel production negates global warming reduction by replacing fossil fuels

The relationship, on a global basis, between the amount of N fixed by chemical, biological or atmospheric processes entering the terrestrial biosphere, and the total emission of nitrous oxide (N2O), has been re-examined, using known global atmospheric removal rates and concentration growth of N2O as a proxy for overall emissions. For both the pre-industrial period and in recent times, after taking into account the large-scale changes in synthetic N fertiliser production, we find an overall conversion factor of 3–5 % from newly fixed N to N2O–N. We assume the same factor to be valid for biofuel production systems. It is covered only in part by the default conversion factor for ‘direct’ emissions from agricultural crop lands (1 %) estimated by IPCC (2006), and the default factors for the ‘indirect’ emissions (following volalilization/deposition and leaching/runoff of N: 0.35–0.45 %) cited therein. However, as we show in the paper, when additional emissions included in the IPCC methodology, e.g. those from livestock production, are included, the total may not be inconsistent with that given by our “top-down” method. When the extra N2O emission from biofuel production is calculated in “CO2-equivalent” global warming terms, and compared with the quasi-cooling effect of ‘saving’ emissions of fossil fuel derived CO2, the outcome is that the production of commonly used biofuels, such as biodiesel from rapeseed and bioethanol from corn (maize), depending on N fertilizer uptake efficiency by the plants, can contribute as much or more to global warming by N2O emissions than cooling by fossil fuel savings. Crops with less N demand, such as grasses and woody coppice species, have more favourable climate impacts. This analysis only considers the conversion of biomass to biofuel. It does not take into account the use of fossil fuel on the farms and for fertilizer and pesticide production, but it also neglects the production of useful co-products. Both factors partially compensate each other. This needs to be analyzed in a full life cycle assessment

AUTOMATED GAS SAMPLING SYSTEM FOR LABORATORY ANALYSIS OF CH\u3csub\u3e4\u3c/sub\u3e AND N\u3csub\u3e2\u3c/sub\u3eO

Analyzing the flux of CH4 and N2O from soil is labor intensive when conventional hand injection techniques are utilized in gas chromatography. An automated gas sampling system was designed and assembled from a prototype developed at the National Soil Tilth Laboratory in Ames, IA. The sampler was evaluated for accuracy and precision when attached to a Varian 3700 gas chromatograph configured with flame ionization and electron capture detectors. The automated gas sampling system is easy to operate and provides acceptable results (standards ranging from 1.0–5.0 ppmv CH4 and 0.342–2.0 ppmv N2O had coefficients of variation ranging from 1.7–5.6%) while providing an economical approach for analyzing large numbers of gas samples with minimal labor and equipment cost

CO2 enhances productivity, alters species composition, and reduces digestibility of Shortgrass Steppe vegetation

Includes bibliographical references (pages 218-219).The impact of increasing atmospheric CO2 concentrations has been studied in a number of field experiments, but little information exists on the response of semiarid rangelands to CO2, or on the consequences for forage quality. This study was initiated to study the CO2 response of the shortgrass steppe, an important semiarid grassland on the western edge of the North American Great Plains, used extensively for livestock grazing. The experiment was conducted for five years on native vegetation at the USDA-ARS Central Plains Experimental Range in northeastern Colorado, USA. Three perennial grasses dominate the study site, Bouteloua gracilis, a C4 grass, and two C3 grasses, Pascopyrum smithii and Stipa comata. The three species comprise 88% of the aboveground phytomass. To evaluate responses to rising atmospheric CO2, we utilized six open-top chambers, three with ambient air and three with air CO2 enriched to 720 mmol/mol, as well as three unchambered controls. We found that elevated CO2 enhanced production of the shortgrass steppe throughout the study, with 41% greater aboveground phytomass harvested annually in elevated compared to ambient plots. The CO2-induced production response was driven by a single species, S. comata, and was due in part to greater seedling recruitment. The result was species movement toward a composition more typical of the mixed-grass prairie. Growth under elevated CO2 reduced the digestibility of all three dominant grass species. Digestibility was also lowest in the only species to exhibit a CO2-induced production enhancement, S. comata. The results suggest that rising atmospheric CO2 may enhance production of lower quality forage and a species composition shift toward a greater C3 component

Effect of elevated carbon dioxide on growth and nitrogen fixation of two soybean cultivars in northern China

The effect of elevated carbon dioxide (CO2) concentration on symbiotic nitrogen fixation in soybean under open-air conditions has not been reported. Two soybean cultivars (Glycine max (L.) Merr. cv. Zhonghuang 13 and cv. Zhonghuang 35) were grown to maturity under ambient (415 ± 16 μmol mol -1) and elevated (550 ± 17 μmol mol -1) [CO2] at the free-air carbon dioxide enrichment experimental facility in northern China. Elevated [CO2] increased above- and below-ground biomass by 16-18% and 11-20%, respectively, but had no significant effect on the tissue C/N ratio at maturity. Elevated [CO2] increased the percentage of N derived from the atmosphere (%Ndfa, estimated by natural abundance) from 59% to 79% for Zhonghuang 13, and the amount of N fixed from 166 to 275 kg N ha -1, but had no significant effect on either parameter for Zhonghuang 35. These results suggest that variation in N2 fixation ability in response to elevated [CO2] should be used as key trait for selecting cultivars for future climate with respect to meeting the higher N demand driven by a carbon-rich atmosphere

Long-term enhancement of N availability and plant growth under elevated CO2 in a semi-arid grassland

1. While rising atmospheric CO2 has the potential to enhance plant growth and biomass accumulation, rates of these processes may be constrained by soil nitrogen (N) availability. Despite much effort, it is still uncertain how elevated CO2 affects long-term soil N dynamics. 2. We used open-top chambers to examine the effect of 5 years of elevated atmospheric CO2 concentration (720 vs. 368 p.p.m.) on N dynamics in a semi-arid grassland ecosystem in north-eastern Colorado, USA. In the first year 0.5 g m-2 of ammonium nitrate-N, 99.9 atom% 15N, was added to each plot. We examined the effect of elevated CO2 on N mineralization and plant N uptake by tracking the labelled and total N in plant and soil over the following 5 years. 3. Plant growth and plant N uptake remained significantly higher under elevated than under ambient CO2. The fraction of labelled N (expressed per unit of total N) in above-ground biomass declined over time, and this decline was greater under elevated CO2. The amount and fraction of labelled N in the soil did not change with time and was unaffected by elevated CO2. These results suggest that with time, N released from mineralization in the soil diluted the labelled N in above-ground biomass and that this dilution effect caused by N mineralization was greater under elevated CO2. More of the mineralized N ended up in the above-ground biomass of Stipa comata and forbs (C3) than in Bouteloua gracilis (C4) under elevated CO2. 4. Increased soil moisture under elevated CO2 likely supported higher rates of N mineralization, thereby reducing N constraints on plant growth. Therefore, in semi-arid systems, plant growth and species composition responses to elevated CO2 may be more persistent than in mesic systems where N mineralization is less constrained by soil moisture

Net Global Warming Potential and Greenhouse Gas Intensity in Irrigated Cropping Systems in Northeastern Colorado

The impact of management on global warming potential (GWP), crop production, and greenhouse gas intensity (GHGI) in irrigated agriculture is not well documented. A no-till (NT) cropping systems study initiated in 1999 to evaluate soil organic carbon (SOC) sequestration potential in irrigated agriculture was used in this study to make trace gas flux measurements for 3 yr to facilitate a complete greenhouse gas accounting of GWP and GHGI. Fluxes of CO2, CH4, and N2O were measured using static, vented chambers, one to three times per week, year round, from April 2002 through October 2004 within conventional-till continuous corn (CT-CC) and NT continuous corn (NT-CC) plots and in NT corn–soybean rotation (NT-CB) plots. Nitrogen fertilizer rates ranged from 0 to 224 kgN ha-1. Methane fluxes were small and did not differ between tillage systems. Nitrous oxide fluxes increased linearly with increasing N fertilizer rate each year, but emission rates varied with years. Carbon dioxide efflux was higher in CT compared to NT in 2002 but was not different by tillage in 2003 or 2004. Based on soil respiration and residue C inputs, NT soils were net sinks of GWP when adequate fertilizer was added to maintain crop production. The CT soils were smaller net sinks for GWP than NT soils. The determinant for the net GWP relationship was a balance between soil respiration and N2O emissions. Based on soil C sequestration, only NT soils were net sinks for GWP. Both estimates of GWP and GHGI indicate that when appropriate crop production levels are achieved, net CO2 emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer

Effects of lignite application on ammonia and nitrous oxide emissions from cattle pens

Beef cattle feedlots are a major source of ammonia (NH3) emissions from livestock industries. We investigated the effects of lignite surface applications on NH3 and nitrous oxide (N2O) emissions from beef cattle feedlot pens. Two rates of lignite, 3 and 6 kg m− 2, were tested in the treatment pen. No lignite was applied in the control pen. Twenty-four Black Angus steers were fed identical commercial rations in each pen. We measured NH3 and N2O concentrations continuously from 4th Sep to 13th Nov 2014 using Quantum Cascade Laser (QCL) NH3 analysers and a closed-path Fourier Transform Infrared Spectroscopy analyser (CP-FTIR) in conjunction with the integrated horizontal flux method to calculate NH3 and N2O fluxes. During the feeding period, 16 and 26% of the excreted nitrogen (N) (240 g N head− 1 day− 1) was lost via NH3 volatilization from the control pen, while lignite application decreased NH3 volatilization to 12 and 18% of the excreted N, for Phase 1 and Phase 2, respectively. Compared to the control pen, lignite application decreased NH3 emissions by approximately 30%. Nitrous oxide emissions from the cattle pens were small, 0.10 and 0.14 g N2O-N head− 1 day− 1 (\u3c 0.1% of excreted N) for the control pen, for Phase 1 and Phase 2, respectively. Lignite application increased direct N2O emissions by 40 and 57%, to 0.14 and 0.22 g N2O-N head− 1 day− 1, for Phase 1 and Phase 2, respectively. The increase in N2O emissions resulting from lignite application was counteracted by the lower indirect N2O emission due to decreased NH3 volatilization. Using 1% as a default emission factor of deposited NH3 for indirect N2O emissions, the application of lignite decreased total N2O emissions