Contribution of N2O to the greenhouse gas balance of first-generation biofuels

In this study, we analyze the impact of fertilizer‐ and manure‐induced N₂O emissions due to energy crop production on the reduction of greenhouse gas (GHG) emissions when conventional transportation fuels are replaced by first‐generation biofuels (also taking account of other GHG emissions during the entire life cycle). We calculate the nitrous oxide (N₂O) emissions by applying a statistical model that uses spatial data on climate and soil. For the land use that is assumed to be replaced by energy crop production (the ‘reference land‐use system’), we explore a variety of options, the most important of which are cropland for food production, grassland, and natural vegetation. Calculations are also done in the case that emissions due to energy crop production are fully additional and thus no reference is considered. The results are combined with data on other emissions due to biofuels production that are derived from existing studies, resulting in total GHG emission reduction potentials for major biofuels compared with conventional fuels. The results show that N₂O emissions can have an important impact on the overall GHG balance of biofuels, though there are large uncertainties. The most important ones are those in the statistical model and the GHG emissions not related to land use. Ethanol produced from sugar cane and sugar beet are relatively robust GHG savers: these biofuels change the GHG emissions by −103% to −60% (sugar cane) and −58% to −17% (sugar beet), compared with conventional transportation fuels and depending on the reference land‐use system that is considered. The use of diesel from palm fruit also results in a relatively constant and substantial change of the GHG emissions by −75% to −39%. For corn and wheat ethanol, the figures are −38% to 11% and −107% to 53%, respectively. Rapeseed diesel changes the GHG emissions by −81% to 72% and soybean diesel by −111% to 44%. Optimized crop management, which involves the use of state‐of‐the‐art agricultural technologies combined with an optimized fertilization regime and the use of nitrification inhibitors, can reduce N₂O emissions substantially and change the GHG emissions by up to −135 percent points (pp) compared with conventional management. However, the uncertainties in the statistical N₂O emission model and in the data on non‐land‐use GHG emissions due to biofuels production are large; they can change the GHG emission reduction by between −152 and 87 pp.     

The greenhouse gas balance of European grasslands

The greenhouse gas (GHG) balance of European grasslands (EU‐28 plus Norway and Switzerland), including CO₂, CH₄ and N₂O, is estimated using the new process‐based biogeochemical model ORCHIDEE‐GM over the period 1961–2010. The model includes the following: (1) a mechanistic representation of the spatial distribution of management practice; (2) management intensity, going from intensively to extensively managed; (3) gridded simulation of the carbon balance at ecosystem and farm scale; and (4) gridded simulation of N₂O and CH₄ emissions by fertilized grassland soils and livestock. The external drivers of the model are changing animal numbers, nitrogen fertilization and deposition, land‐use change, and variable CO₂ and climate. The carbon balance of European grassland (NBP) is estimated to be a net sink of 15 ± 7 g C m^?2 year^?1 during 1961–2010, equivalent to a 50‐year continental cumulative soil carbon sequestration of 1.0 ± 0.4 Pg C. At the farm scale, which includes both ecosystem CO₂ fluxes and CO₂ emissions from the digestion of harvested forage, the net C balance is roughly halved, down to a small sink, or nearly neutral flux of 8 g C m^?2 year^?1. Adding CH₄ and N₂O emissions to net ecosystem exchange to define the ecosystem‐scale GHG balance, we found that grasslands remain a net GHG sink of 19 ± 10 g C‐CO₂ equiv. m^?2 year^?1, because the CO₂ sink offsets N₂O and grazing animal CH₄ emissions. However, when considering the farm scale, the GHG balance (NGB) becomes a net GHG source of ?50 g C‐CO₂ equiv. m^?2 year^?1. ORCHIDEE‐GM simulated an increase in European grassland NBP during the last five decades. This enhanced NBP reflects the combination of a positive trend of net primary production due to CO₂, climate and nitrogen fertilization and the diminishing requirement for grass forage due to the Europe‐wide reduction in livestock numbers.     

Real‐time monitoring of greenhouse gas emissions with tall chambers reveals diurnal N2O variation and increased emissions of CO2 and N2O from Miscanthus following compost addition

Miscanthus x giganteus's efficacy as an energy crop relies on maintaining low greenhouse gas (GHG) emissions. As demand for Miscanthus is expected to rise to meet bioenergy targets, fertilizers and composts may be employed to increase yields, but will also increase GHG emissions. Manipulation experiments are vital to investigate the consequences of any fertilizer additions, but there is currently no way to measure whole‐plant GHG fluxes from crops taller than 2.5 m, such as Miscanthus, at the experimental plot scale. We employed a unique combination of eddy covariance (EC), soil chambers and an entirely new automated chamber system, SkyBeam, to measure high frequency (ca. hourly) fluxes of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) from a Miscanthus crop amended with green compost. Untreated controls were also monitored in a fully replicated experimental design. Net ecosystem exchange (NEE) of CO₂ was partitioned into soil respiration (R_s), gross primary productivity (GPP) and ecosystem respiration, and the crop was harvested to determine the effect of compost on crop productivity. Compost increased NEE emissions by 100% (p < .05), which was the result of a 20% increase of R_s (p < .06) and a 32% reduction in GPP (p < .05) and biomass of 37% (p < .06). Methane fluxes were small and unaffected by compost addition. N₂O emissions increased 34% under compost during an emission event; otherwise, fluxes were low and often negative, even under dry conditions. Diurnal variation in N₂O fluxes, with uptake during the day and emission at night was observed. These fluxes displayed a negative relationship with soil temperature and a hitherto undescribed diurnal temperature hysteresis. We conclude that compost addition negatively affected the productivity and environmental effects of Miscanthus cultivation during the first year following application.     

A first‐generation microsatellite linkage map of the ruff

A linkage map of the ruff (Philomachus pugnax) genome was constructed based on segregation analysis of 58 microsatellite loci from 381 captive‐bred individuals spanning fourteen breeding years and comprising 64 families. Twenty‐eight of the markers were resolved into seven linkage groups and five single marker loci, homologous to known chicken (Gallus gallus) and zebra finch (Taeniopygia guttata) chromosomes. Linkage groups range from 10.1 to 488.7 cM in length and covered a total map distance of 641.6 cM, corresponding to an estimated 30–35% coverage of the ruff genome, with a mean spacing of 22.9 cM between loci. Through comparative mapping, we are able to assign linkage groups Ppu1, Ppu2, Ppu6, Ppu7, Ppu10, Ppu13, and PpuZ to chromosomes and identify several intrachromosomal rearrangements between the homologs of chicken, zebra finch, and ruff microsatellite loci. This is the first linkage map created in the ruff and is a major step toward providing genomic resources for this enigmatic species. It will provide an essential framework for mapping of phenotypically and behaviorally important loci in the ruff.     

The contribution of PAS 2050 to the evolution of international greenhouse gas emission standards

Background, aim, and scope  The assessment of greenhouse gas (GHG) emissions arising from products (goods and services) is emerging as a high profile application of life cycle assessment (LCA), with an increasing desire from retailers and other supply chain organizations to better understand, and in some cases communicate, the carbon footprint of products. Publicly Available Specification 2050:2008, Specification for the assessment of the life cycle greenhouse gas emissions of goods and services, addresses the single-impact category of global warming to provide a standardized and simplified implementation of process LCA methods for assessing GHG emissions from products. This paper briefly reviews the development process followed for PAS 2050, before examining the treatment of GHG-specific contribution of PAS 2050 to product carbon footprinting. Materials and methods  PAS 2050 was jointly sponsored by the Carbon Trust and the UK Department for Environment, Food and Rural Affairs and was published by the British Standards Institution on 29 October 2008. An independent steering group oversaw the development of the specification, including the establishment of an expert workgroup program, comprehensive international consultation, and expert input on the requirements of the specification. Results  The development process for PAS 2050 resulted in a specification that includes specific requirements that limit the interpretation of the underlying LCA approach to product carbon footprinting. These requirements, including goal setting and life cycle inventory assessment, aspects of system boundary identification and temporal aspects of GHG emissions, clarify the approach to be taken by organizations implementing product carbon footprinting, and simplify the application of LCA procedures in relation to product carbon footprinting. Discussion  Assessment of the emissions arising from the life cycle of products has a clear international component, and delivering consistent results across the supply chain requires the application of consistent methods. There is an emerging recognition that further standardization of methods for product carbon footprinting is needed, and the specific requirements resulting from the PAS 2050 development process make a valuable contribution across a range of GHG assessment issues. Conclusions  The widespread interest in PAS 2050 from individuals and organizations, together with the development of similar guidance by other organizations, confirmed that there is a need for clarification, certainty, and requirements in the field of product carbon footprint analysis. The use of PAS 2050 to refine, clarify, and simplify existing LCA methods and standards has resulted in specific approaches to key GHG assessment issues being developed; it is important that future standards development work considers the impact of these approaches and their further refinement. Recommendations and perspectives  It is the consumption of goods and services by individuals around the world that drives global GHG emission, and PAS 2050 is a first attempt to provide integrated, consistent approaches that directly address the role of consumption at the product level in contributing to GHG emissions. Climate science and GHG assessment techniques are both evolving areas and it will be necessary to review the approach taken by PAS 2050 in the future: a formal review process for PAS 2050 will commence towards the end of 2009 and practitioners are encouraged to participate in this review process.

Life cycle assessment of biofuels: Energy and greenhouse gas balances

The promotion of biofuels as energy for transportation in the industrialized countries is mainly driven by the perspective of oil depletion, the concerns about energy security and global warming. However due to sustainability constraints, biofuels will replace only 10 to 15% of fossil liquid fuels in the transport sector. Several governments have defined a minimum target of GHG emissions reduction for those biofuels that will be eligible to public incentives, for example a 35% emissions reduction in case of biofuels in Members States of the European Union. This article points out the significant biases in estimating GHG balances of biofuels stemming from modelling choices about system definition and boundaries, functional unit, reference systems and allocation methods. The extent to which these choices influence the results is investigated. After performing a comparison and constructive criticism of various modelling choices, the LCA of wheat-to-bioethanol is used as an illustrative case where bioethanol is blended with gasoline at various percentages (E5, E10 and E85). The performance of these substitution options is evaluated as well. The results show a large difference in the reduction of the GHG emissions with a high sensitivity to the following factors: the method used to allocate the impacts between the co-products, the type of reference systems, the choice of the functional unit and the type of blend. The authors come out with some recommendations for basing the estimation of energy and GHG balances of biofuels on principles such as transparency, consistency and accuracy.     

Management of biological N2 fixation in alley cropping systems: Estimation and contribution to N balance

Alley cropping is being widely tested in the tropics for its potential to sustain adequate food production with low agricultural inputs, while conserving the resource base. Fast growth and N yield of most trees used as hedgerows in alley cropping is due greatly to their ability to fix N₂ symbiotically with Rhizobium. Measurements of biological N₂ fixation (BNF) in alley cropping systems show that some tree species such as Leucaena leucocephala, Gliricidia sepium and Acacia mangium can derive between 100 and 300 kg N ha^-1 yr^–1 from atmospheric N₂, while species such as Faidherbia albida and Acacia senegal might fix less than 20 kg N ha^-1 yr^-1. Other tree species such as Senna siamea and S. spectabilis are also used in alley cropping, although they do not nodulate and therefore do not fix N₂. The long-term evaluation of the potential or actual amounts of N₂ fixed in trees however, poses problems that are associated with their perennial nature and massive size, the great difficulty in obtaining representative samples and applying reliable methodologies for measuring N₂ fixed. Strategies for obtaining representative samples (as against the whole tree or destructive plant sampling), the application of ¹⁵N procedures and the selection criteria for appropriate reference plants have been discussed.Little is known about the effect of environmental factors and management practices such as tree cutting or pruning and residue management on BNF and eventually their N contribution in alley cropping. Data using the ¹⁵N labelling techniques have indicated that up to 50% or more of the tree's N may be below ground after pruning. In this case, quantification of N₂ fixed that disregards roots, nodules and crowns would result in serious errors and the amount of N₂ fixed may be largely underestimated. Large quantities of N are harvested with hedgerow prunings (>300 kg N ha^-1 yr^-1) but N contribution to crops is commonly in the range of 40–70 kg N ha^-1 season. This represents about 30% of N applied as prunings; however, N recoveries as low as 5–10% have been reported. The low N recovery in maize (Zea mays) is partly caused by lack of synchronization between the hedgerow trees N release and the associated food crop N demand. The N not taken up by the associated crop can be immobilized in soil organic matter or assimilated by the hedgerow trees and thus remain in the system. This N can also be lost from the system through denitrification, volatilization or is leached beyond the rooting zone. Below ground contribution (from root turnover and nodule decay) to an associated food crop in alley cropping is estimated at about 25–102 kg N ha^-1 season^-1. Timing and severity of pruning may allow for some management of underground transfer of fixed N₂ to associated crops. However many aspects of root dynamics in alley cropping systems are poorly understood. Current research projects based on ¹⁵N labelling techniques or ¹⁵N natural abundance measurements are outlined. These would lead to estimates of N₂ fixation and N saving resulting from the management of N₂ fixation in alley cropping systems.     

Temporal trends in N2O flux dynamics in a Danish wetland – effects of plant‐mediated gas transport of N2O and O2 following changes in water level and soil mineral‐N availability

Temporal trends of N₂O fluxes across the soil–atmosphere interface were determined using continuous flux chamber measurements over an entire growing season of a subsurface aerating macrophyte (Phalaris arundinacea) in a nonmanaged Danish wetland. Observed N₂O fluxes were linked to changes in subsurface N₂O and O₂ concentrations, water level (WL), light intensity as well as mineral‐N availability. Weekly concentration profiles showed that seasonal variations in N₂O concentrations were directly linked to the position of the WL and O₂ availability at the capillary fringe above the WL. N₂O flux measurements showed surprisingly high temporal variability with marked changes in fluxes and shifts in flux directions from net source to net sink within hours associated with changing light conditions. Systematic diurnal shifts between net N₂O emission during day time and deposition during night time were observed when max subsurface N₂O concentrations were located below the root zone. Correlation (P < 0.001) between diurnal variations in O₂ concentrations and incoming photosynthetically active radiation highlighted the importance of plant‐driven subsoil aeration of the root zone and the associated controls on coupled nitrification/denitrification. Therefore, P. arundinacea played an important role in facilitating N₂O transport from the root zone to the atmosphere, and exclusion of the aboveground biomass in flux chamber measurements may lead to significant underestimations on net ecosystem N₂O emissions. Complex interactions between seasonal changes in O₂ and mineral‐N availability following near‐surface WL fluctuations in combination with plant‐mediated gas transport by P. arundinacea controlled the subsurface N₂O concentrations and gas transport mechanisms responsible for N₂O fluxes across the soil–atmosphere interface. Results demonstrate the necessity for addressing this high temporal variability and potential plant transport of N₂O in future studies of net N₂O exchange across the soil–atmosphere interface.     

The economics and greenhouse gas balance of land conversion to Jatropha: the case of Tanzania

Due to higher oil prices, abundance of labor and suitable land and its stable political climate, Tanzania attracted many investments in Jatropha. Although several studies on Jatropha's economic potential are available, its true economics are still uncertain. This paper aims to add to the growing body of knowledge on the socio‐economic performance of the Jatropha system by (i) studying the economic potential (net present value – NPV) of the current most prevailing Jatropha system for Tanzanian farmers and its regional differences, by (ii) making a greenhouse gas (GHG) balance and its economic value of the Jatropha activities on regional level, and by (iii) calculating break‐even thresholds for yield and seed price. Therefore, regional yield modeling, regional life‐cycle assessment, and NPV calculations based on Monte Carlo simulations, each with its set of assumptions, are combined. This study shows positive economic potential of Jatropha cultivation in most of the Tanzanian regions. However, the results also show that 13 of 20 Tanzanian regions will not attain a net positive GHG balance within 10 years. This indicates that the environmental impacts might be more restrictive for Jatropha's sustainability potential in Tanzania than the socio‐economic potential. These results are based on the combination of three models, which consists of strong interdisciplinary modeling work. However, this modeling also contains simplifications (e.g., no opportunity cost for ‘marginal’ land) and uncertainties (e.g., using globally modeled potential yield estimations), which have to be considered in the interpretation of the results.     

Global relative species loss due to first‐generation biofuel production for the transport sector

The global demand for biofuels in the transport sector may lead to significant biodiversity impacts via multiple human pressures. Biodiversity assessments of biofuels, however, seldom simultaneously address several impact pathways, which can lead to biased comparisons with fossil fuels. The goal of the present study was to quantify the direct influence of habitat loss, water consumption and greenhouse gas (GHG) emissions on potential global species richness loss due to the current production of first‐generation biodiesel from soybean and rapeseed and bioethanol from sugarcane and corn. We found that the global relative species loss due to biofuel production exceeded that of fossil petrol and diesel production in more than 90% of the locations considered. Habitat loss was the dominating stressor with Chinese corn, Brazilian soybean and Brazilian sugarcane having a particularly large biodiversity impact. Spatial variation within countries was high, with 90th percentiles differing by a factor of 9 to 22 between locations. We conclude that displacing fossil fuels with first‐generation biofuels will likely negatively affect global biodiversity, no matter which feedstock is used or where it is produced. Environmental policy may therefore focus on the introduction of other renewable options in the transport sector.     

Nitrogen fertilization to optimize the greenhouse gas balance of hemp crops grown for biomass

Nitrogen trials were carried out on hemp crops grown in Ireland over a 3 year period to identify nitrogen fertilization strategies which optimize the greenhouse gas (GHG) and energy balances of hemp crops grown for biomass. Nitrogen rates up to 150 kg N ha^?1 were used in the study. Yield increased with nitrogen rate up to 120 kg N ha^?1 for early (Ferimon), mid (Felina 32) and late maturing (Futura 75) varieties. Variety had a significant effect on yield with yields increasing with maturation date. In 2 years of the study, certain application rates of nitrogen were applied either at sowing, at emergence, after emergence or split between these dates to determine if nitrogen rates could be reduced by delaying or splitting the applications. The application of nitrogen at times later than sowing or in splits during the early part of the growing season had no significant effect on biomass yield compared with the practice of applying nitrogen at the time of sowing. Late applications of nitrogen reduced leaf chlorophyll content and height early in the growing season. Later in the growing season, there was no difference in height between treatments although the highest concentrations of chlorophyll were found in the leaves of the late application treatment. Nitrogen rate and the timing of nitrogen application had no effect on plant density. Biomass yield, net energy and net GHG mitigation increased up to an application rate of 120 kg N ha^?1, this result was independent of soil type or soil nitrogen level. Net GHG and energy balance of hemp crops grown for biomass are optimized if late maturing varieties are used for biomass production and a nitrogen rate of 120 kg ha^?1 is applied at sowing.     

Biological N2 Fixation in wetland rice fields: Estimation and contribution to nitrogen balance

This paper 1) reviews improvements and new approaches in methodologies for estimating biological N₂ fixation (BNF) in wetland soils, 2) summarizes earlier quantitative estimates and recent data, and 3) discusses the contribution of BNF to N balance in wetland-rice culture.Measuring acetylene reducing activity (ARA) is still the most popular method for assessing BNF in rice fields. Recent studies confirm that ARA measurements present a number of problems that may render quantitative extrapolations questionable. On the other hand, few comparative measures show ARA's potential as a quantitative estimate. Methods for measuring photodependent and associative ARA in field studies have been standardized, and major progress has been made in sampling procedures. Standardized ARA measurements have shown significant differences in associative N₂ fixation among rice varieties.The ¹⁵N dilution method is suitable for measuring the percentage of N derived from the atmosphere (% Ndfa) in legumes and rice. In particular, the ¹⁵N dilution technique, using available soil N as control, appears to be a promising method for screening rice varieties for ability to utilize biologically fixed N. Attempts to adapt the ¹⁵N dilution method to aquatic N₂ fixers (Azolla and blue-green algae [BGA]) encountered difficulties due to the rapid change in ¹⁵N enrichment of the water.Differences in natural ¹⁵N abundance have been used to show differences among plant organs and species or varieties in rice and Azolla, and to estimate Ndfa by Azolla, but the method appears to be semi-quantitative.Recent pot experiments using stabilized ¹⁵N-labelled soil or balances in pots covered with black cloth indicate a contribution of 10–30 kg N ha^-1 crop^-1 by heterotrophic BNF in flooded planted soil with no or little N fertilizer used.Associative BNF extrapolated from ARA and ¹⁵N incorporation range from 1 to 7 kg N ha^-1 crop^-1. Straw application increases heterotrophic and photodependent BNF. Pot experiments show N gains of 2–4 mg N g^-1 straw added at 10 tons ha^-1.N₂ fixation by BGA has been almost exclusively estimated by ARA and biomass measurements. Estimates by ARA range from a few to 80 kg N ha^-1 crop^-1 (average 27 kg). Recent extensive measurements show extrapolated values of about 20 kg N ha^-1 crop^-1 in no-N plots, 8 kg in plots with broadcast urea, and 12 kg in plots with deep-placed urea.Most information on N₂ fixed by Azolla and legume green manure comes from N accumulation measurements and determination of % Ndfa. Recent trials in an international network show standing crops of Azolla averaging 30–40 kg N ha^-1 and the accumulation of 50–90 kg N ha^-1 for two crops of Azolla grown before and after transplanting rice. Estimates of % Ndfa in Azolla by ¹⁵N dilution and delta ¹⁵N methods range from 51 to 99%. Assuming 50–80% Ndfa in legume green manures, one crop can provide 50–100 kg N ha^-1 in 50 days. Few balance studies in microplots or pots report extrapolated N gains of 150–250 kg N ha^-1 crop^-1.N balances in long-term fertility experiments range from 19 to 98 kg N ha^-1 crop^-1 (average 50 kg N) in fields with no N fertilizer applied. The problems encountered with ARA and ¹⁵N methods have revived interest in N balance studies in pots. Balances are usually highest in flooded planted pots exposed to light and receiving no N fertilizer; extrapolated values range from 16 to 70 kg N ha^-1 crop^-1 (average 38 kg N). A compilation of balance experiments with rice soil shows an average balance of about 30 kg N ha^-1 crop^-1 in soils where no inorganic fertilizer N was applied.Biological N₂ fixation by individual systems can be estimated more or less accurately, but total BNF in a rice field has not yet been estimated by measuring simultaneously the activities of the various components in situ. As a result, it is not clear if the activities of the different N₂-fixing systems are independent or related. A method to estimate in situ the contribution of N₂ fixed to rice nutrition is still not available. Dynamics of BNF during the crop cycle is known for indigenous agents but the pattern of fixed N availability to rice is known only for a few green manure crops.     

我国北方几种玉米和设施菜地土壤的N2O和N2排放特征

为了探究旱地土壤施入氮肥后的气态氮(N2O和N2)损失规律,本研究通过室内好氧培养试验(60 d,25℃,80％孔隙含水量),运用15N同位素示踪技术,研究了4个玉米地土壤(哈尔滨、沈阳、栾城、寿光)和2个设施菜地土壤(沈阳、寿光)在施入尿素后的氮转化、N2O和N2排放动态.试验中尿素添加量为167 mg N·kg-1...     

Give them credit‐the greenhouse gas performance of regional biogas systems

Anaerobic digestion to produce biogas is an important decentralised renewable energy technology. Production varies extensively between different countries and within countries, as biogas production is heavily dependent on local and regional feedstocks. In Germany, distinct regional differences can be observed. Therefore, understanding the kinds of biogas systems operating within a region is crucial to determine their greenhouse gas (GHG) mitigation potential and carbon neutrality. This is the first study to conduct an integrated life cycle assessment of biogas configurations in the landscape (biogas plants and their biomass catchments) for an entire region. RELCA a ‘REgional Life Cycle inventory Assessment’ approach was used to model the GHG mitigation potential of 425 biogas plants in the region of Central Germany (CG), aggregated to nine biogas clusters, based on feedstock mix (e.g. animal manures and energy crops) and installed capacity. GHG emission profiles were generated to compare and to identify the role of GHG credits and size of installed capacity on the mitigation performance of the regional biogas clusters. We found that smaller scaled slurry dominant clusters had significantly better GHG mitigation performance (?0.1 to ?0.2 kg CO_2eq kWh_el^?1), than larger energy crop dominant (EC_dom) clusters (0.04–0.16 kg CO_2eq kWh_el^?1), due to lower cultivation emissions and larger credits for avoided slurry storage. Thus, for the CG region larger EC_dom clusters should be targeted first, to support GHG mitigation improvements to the overall future electricity supplied by the regional biogas systems. With the addition of GHG credits, the CG region is producing biogas with GHG savings (?0.15 kg CO_2eq kWh_el^?1, interquartile range: 0.095 kg CO_2eq kWh_el^?1). This infers that biogas production, as a waste management strategy for animal manures, could have important ramifications for future policy setting and national inventory accounting.     

Evidence from field nitrogen balance and 15N natural abundance data for the contribution of biological N2 fixation to Brazilian sugarcane varieties

Aims

In Brazil N fertilization of sugarcane (Saccharum spp.) is low compared to most other countries. ¹⁵N-aided studies and the occurrence of many N₂-fixing bacteria associated with cane plants suggest significant contributions from biological N₂ fixation (BNF). The objective of this study was to evaluate BNF contributions to nine cane varieties under field conditions using N balance and ¹⁵N natural abundance techniques.

Methods

The field experiment was planted near Rio de Janeiro in 1989, replanted in 1999 and harvested 13 times until 2004. Soil total N was evaluated at planting and again in 2004. Samples of cane leaves and weeds for the evaluation of ¹⁵N natural abundance were taken in 2000, 2003 and 2004.

Results

N accumulation of the commercial cane varieties and a variety of Saccharum spontaneum were persistently high and N balances (60 to 107?kg?N ha^?1?yr^?1) significantly (p?<?0.05) positive. The δ¹⁵N of leaf samples were lower than any of the weed reference plants and data obtained from a greenhouse study indicated that this was not due to the cane plants tapping into soil of lower ¹⁵N abundance at greater depth.

Conclusion

The results indicate that the Brazilian varieties of sugarcane were able to obtain at least 40?kg?N ha^?1?yr^?1 from BNF.     

The role of N2O derived from crop-based biofuels, and from agriculture in general, in Earth's climate

In earlier work, we compared the amount of newly fixed nitrogen (N, as synthetic fertilizer and biologically fixed N) entering agricultural systems globally to the total emission of nitrous oxide (N(2)O). We obtained an N(2)O emission factor (EF) of 3-5%, and applied it to biofuel production. For 'first-generation' biofuels, e.g. biodiesel from rapeseed and bioethanol from corn (maize), that require N fertilizer, N(2)O from biofuel production could cause (depending on N uptake efficiency) as much or more global warming as that avoided by replacement of fossil fuel by the biofuel. Our subsequent calculations in a follow-up paper, using published life cycle analysis (LCA) models, led to broadly similar conclusions. The N(2)O EF applies to agricultural crops in general, not just to biofuel crops, and has made possible a top-down estimate of global emissions from agriculture. Independent modelling by another group using bottom-up IPCC inventory methodology has shown good agreement at the global scale with our top-down estimate. Work by Davidson showed that the rate of accumulation of N(2)O in the atmosphere in the late nineteenth and twentieth centuries was greater than that predicted from agricultural inputs limited to fertilizer N and biologically fixed N (Davidson, E. A. 2009 Nat. Geosci. 2, 659-662.). However, by also including soil organic N mineralized following land-use change and NO(x) deposited from the atmosphere in our estimates of the reactive N entering the agricultural cycle, we have now obtained a good fit between the observed atmospheric N(2)O concentrations from 1860 to 2000 and those calculated on the basis of a 4 per cent EF for the reactive N.     

Selection of broad‐spectrum cephalosporin‐resistant Escherichia coli in the feces of healthy dogs after administration of first‐generation cephalosporins

Although antimicrobial products are essential for treating diseases caused by bacteria, antimicrobial treatment selects for antimicrobial‐resistant (AMR) bacteria. The aim of this study was to determine the effects of administration of first‐generation cephalosporins on development of resistant Escherichia coli in dog feces. The proportions of cephalexin (LEX)‐resistant E. coli in fecal samples of three healthy dogs treated i.v. with cefazolin before castration and then orally with LEX for 3 days post‐operation (PO) were examined using DHL agar with or without LEX (50 µg/mL). LEX‐resistant E. coli were found within 3 days PO, accounted for 100% of all identified E. coli 3–5 days PO in all dogs, and were predominantly found until 12 days PO. LEX‐resistant E. coli isolates on DHL agar containing LEX were subjected to antimicrobial susceptibility testing, pulsed‐field gel electrophoresis (PFGE) genotyping, β‐lactamase typing and plasmid profiling. All isolates tested exhibited cefotaxime (CTX) resistance (CTX minimal inhibitory concentration ≥4 µg/mL). Seven PFGE profiles were classified into five groups and three β‐lactamase combinations (bla_CMY‐4‐bla_TEM‐1, bla_TEM‐1‐bla_CTX‐M‐15 and bla_TEM‐1‐bla_CTX‐M‐15‐bla_CMY‐4). All isolates exhibited identical PFGE profiles in all dogs on four days PO and subsequently showed divergent PFGE profiles. Our results indicate there are two selection periods for AMR bacteria resulting from the use of antimicrobials. Thus, continuing hygiene practices are necessary to prevent AMR bacteria transfer via dog feces after antimicrobial administration.     

The contribution of nitrogen transformation processes to total N2O emissions from soils used for intensive vegetable cultivation

The rapid expansion of intensively farmed vegetable fields has substantially contributed to the total N₂O emissions from croplands in China. However, to date, the mechanisms underlying this phenomenon have not been completely understood. To quantify the contributions of autotrophic nitrification, heterotrophic nitrification, and denitrification to N₂O production from the intensive vegetable fields and to identify the affecting factors, a ¹⁵N tracing experiment was conducted using five soil samples collected from adjacent fields used for rice-wheat rotation system (WF), or for consecutive vegetable cultivation (VF) for 0.5 (VF1), 6 (VF2), 8 (VF3), and 10 (VF4) years. Soil was incubated under 50% water holding capacity (WHC) at 25°C for 96 h after being labeled with ¹⁵NH₄NO₃ or NH ₄ ¹⁵ NO₃. The average N₂O emission rate was 24.2 ng N?kg^?1 h^?1 in WF soil, but it ranged from 69.6 to 507 ng N?kg^?1 h^?1 in VF soils. Autotrophic nitrification, heterotrophic nitrification and denitrification accounted for 0.3–31.4%, 25.4–54.4% and 22.5–57.7% of the N₂O emissions, respectively. When vegetable soils were moderately acidified (pH, 6.2 to ?≥?5.7), the increased N₂O emissions resulted from the increase of both the gross autotrophic and heterotrophic nitrification rates and the N₂O product ratio of autotrophic nitrification. However, once severe acidification occurred (as in VF4, pH?≤?4.3) and salt stress increased, both autotrophic and heterotrophic nitrification rates were inhibited to levels similar to those of WF soil. The enhanced N₂O product ratios of heterotrophic nitrification (4.84‰), autotrophic nitrification (0.93‰) and denitrification processes were the most important factors explaining high N₂O emission in VF4 soil. Data from this study showed that various soil conditions (e.g., soil salinity and concentration of NO ₃ ^- or NH ₄ ⁺ ) could also significantly affect the sources and rates of N₂O emission.