Ecological and physiological implications of nitrogen oxide reduction pathways on greenhouse gas emissions in agroecosystems

2019 ◽  
Vol 95 (6) ◽  
Author(s):  
Sukhwan Yoon ◽  
Bongkeun Song ◽  
Rebecca L Phillips ◽  
Jin Chang ◽  
Min Joon Song
Keyword(s):  
Reductase Activity ◽  
Ghg Emissions ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
Oxide Reduction ◽  
N Budget ◽  
Ghg Mitigation ◽  
N Losses ◽  
N2o Production ◽  
N2o Reductase

ABSTRACT Microbial reductive pathways of nitrogen (N) oxides are highly relevant to net emissions of greenhouse gases (GHG) from agroecosystems. Several biotic and abiotic N-oxide reductive pathways influence the N budget and net GHG production in soil. This review summarizes the recent findings of N-oxide reduction pathways and their implications to GHG emissions in agroecosystems and proposes several mitigation strategies. Denitrification is the primary N-oxide reductive pathway that results in direct N2O emissions and fixed N losses, which add to the net carbon footprint. We highlight how dissimilatory nitrate reduction to ammonium (DNRA), an alternative N-oxide reduction pathway, may be used to reduce N2O production and N losses via denitrification. Implications of nosZ abundance and diversity and expressed N2O reductase activity to soil N2O emissions are reviewed with focus on the role of the N2O-reducers as an important N2O sink. Non-prokaryotic N2O sources, e.g. fungal denitrification, codenitrification and chemodenitrification, are also summarized to emphasize their potential significance as modulators of soil N2O emissions. Through the extensive review of these recent scientific advancements, this study posits opportunities for GHG mitigation through manipulation of microbial N-oxide reductive pathways in soil.

Opportunities to reduce nitrous oxide emissions from horticultural production systems in Canada

2021 ◽  
Author(s):  
Inderjot Chahal ◽  
Khagendra R. Baral ◽  
Kate A. Congreves ◽  
Laura L. Van Eerd ◽  
C. Wagner-Riddle
Keyword(s):  
Cover Crops ◽  
Production Systems ◽  
Current Knowledge ◽  
N Fertilizer ◽  
Mitigation Strategies ◽  
Nitrous Oxide Emissions ◽  
N2o Emissions ◽  
N Losses ◽  
N2o Production ◽  
Fertilizer Application Rate

Horticultural systems, specifically vegetable production systems, are considered intensive agricultural systems as they are characterized by high nitrogen (N) fertilizer application rate, frequent tillage and irrigation operations. Accordingly, horticultural production in temperate climates is prone to N losses—mainly during post-harvest (during fall and winter) or pre-plant (spring) periods—such as N2O emissions and nitrate leaching. The risk for N losses is linked to low crop N use efficiency (NUE) combined with a narrow C:N and high N content of crop residues. Here we reviewed the studies conducted in Canada and similar climates to better understand the risk of N2O emission and potential agronomic management strategies to reduce N2O emissions from horticultural systems. Current knowledge on N2O emissions from horticultural systems indicate that increasing crop NUE, modifying the amount, type, time, and rate of N fertilizer inputs, and adopting cover crops in crop rotations are some of the effective approaches to decrease N2O emissions. However, there is uncertainty related to the efficiency of the existing N2O mitigation strategies due to the complex interactions between the factors (soil characteristics, type of plant species, climatic conditions, and soil microbial activity) responsible for N2O production from soil. Little research on N2O emissions from Canadian horticultural systems limits our ability to understand and manage the soil N2O production processes to mitigate the risk of N2O emissions. Thus, continuing to expand this line of research will help to advance the sustainability of Canadian horticultural cropping systems.

Towards a benchmarking tool for minimizing wastewater utility greenhouse gas footprints

2012 ◽  
Vol 66 (11) ◽  
pp. 2483-2495 ◽  
Author(s):  
L. Guo ◽  
J. Porro ◽  
K. R. Sharma ◽  
Y. Amerlinck ◽  
L. Benedetti ◽  
...  
Keyword(s):  
Activated Sludge ◽  
Greenhouse Gas ◽  
Ghg Emissions ◽  
Treatment Plant ◽  
N2o Emission ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
N2o Production ◽  
Average Value ◽  
And Control

A benchmark simulation model, which includes a wastewater treatment plant (WWTP)-wide model and a rising main sewer model, is proposed for testing mitigation strategies to reduce the system's greenhouse gas (GHG) emissions. The sewer model was run to predict methane emissions, and its output was used as the WWTP model input. An activated sludge model for GHG (ASMG) was used to describe nitrous oxide (N2O) generation and release in activated sludge process. N2O production through both heterotrophic and autotrophic pathways was included. Other GHG emissions were estimated using empirical relationships. Different scenarios were evaluated comparing GHG emissions, effluent quality and energy consumption. Aeration control played a clear role in N2O emissions, through concentrations and distributions of dissolved oxygen (DO) along the length of the bioreactor. The average value of N2O emission under dynamic influent cannot be simulated by a steady-state model subjected to a similar influent quality, stressing the importance of dynamic simulation and control. As the GHG models have yet to be validated, these results carry a degree of uncertainty; however, they fulfilled the objective of this study, i.e. to demonstrate the potential of a dynamic system-wide modelling and benchmarking approach for balancing water quality, operational costs and GHG emissions.

scholarly journals The nitrogen, carbon and greenhouse gas budget of a grazed, cut and fertilised temperate grassland

2016 ◽  
Author(s):  
Stephanie K. Jones ◽  
Carole Helfter ◽  
Margaret Anderson ◽  
Mhairi Coyle ◽  
Claire Campbell ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Soil Layer ◽  
The Body ◽  
Sink Strength ◽  
N2o Emissions ◽  
N Budget ◽  
N Losses ◽  
Enteric Fermentation ◽  
C And N ◽  
Ch4 And N2o

Abstract. Intensively managed grazed grasslands in temperate climates are globally important environments for the exchange of the greenhouse gases (GHGs) carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). We assessed the N and C budget of a mostly grazed, occasionally cut, and fertilized grassland in SE Scotland by measuring or modelling all relevant imports and exports to the field as well as changes in soil C and N pools over time. The N budget was dominated by import from inorganic and organic fertilisers (21.9 g N m2 yr−1) and losses from leaching (5.3 g N m2 yr−1), N2 emissions and NOx and NH3 volatilisation (6.4 g N m2 yr−1). The efficiency of N use by animal products (meat and wool) averaged 11 %. On average over nine years (2002–2010) the balance of N fluxes suggested that 7.2 ± 4.6 g N m−2 y−1 (mean ± confidence interval at p > 0.95) were stored in the soil. The largest component of the C budget was the net ecosystem exchange of CO2 (NEE), at an average uptake rate of 218 ± 155 g C m−2 y−1 over the nine years. This sink strength was offset by carbon export from the field mainly as harvest (48.9 g C m2 yr−1) and leaching (16.4 g C m2 yr−1). The other export terms, CH4 emissions from the soil, manure applications and enteric fermentation were negligible and only contributed to 0.02–4.2 % of the total C losses. Only a small fraction of C was incorporated into the body of the grazing animals. Inclusion of these C losses in the budget resulted in a C sink strength of 163 ± 140 g C m−2 y−1. On the contrary, soil stock measurements taken in May 2004 and May 2011 indicated that the grassland sequestered N in the 0–60 cm soil layer at 4.51 ± 2.64 g N m−2 y−1 and lost C at a rate of 29.08 ± 38.19 g C m−2 y-1, respectively. Potential reasons for the discrepancy between these estimates are probably an underestimation of C and N losses, especially from leaching fluxes as well as from animal respiration. The average greenhouse gas (GHG) balance of the grassland was −366 ± 601 g CO2 eq m−2 y−1 and strongly affected by CH4 and N2O emissions. The GHG sink strength of the NEE was reduced by 54 % by CH4 and N2O emissions. Enteric fermentation from the ruminating sheep proved to be an important CH4 source, exceeding the contribution of N2O to the GHG budget in some years.

scholarly journals A new look at an old concept: using <sup>15</sup>N<sub>2</sub>O isotopomers to understand the relationship between soil moisture and N<sub>2</sub>O production pathways

SOIL ◽  
2019 ◽  
Vol 5 (2) ◽  
pp. 265-274 ◽  
Author(s):  
Katelyn A. Congreves ◽  
Trang Phan ◽  
Richard E. Farrell
Keyword(s):  
Soil Moisture ◽  
Mitigation Strategies ◽  
Soil Conditions ◽  
Site Preference ◽  
N2o Emissions ◽  
Spectroscopic Techniques ◽  
N2o Production ◽  
Nitrification And Denitrification ◽  
The Relationship ◽  
Source Partitioning

Abstract. Understanding the production pathways of potent greenhouse gases, such as nitrous oxide (N2O), is essential for accurate flux prediction and for developing effective adaptation and mitigation strategies in response to climate change. Yet there remain surprising gaps in our understanding and precise quantification of the underlying production pathways – such as the relationship between soil moisture and N2O production pathways. A powerful, but arguably underutilized, approach for quantifying the relative contribution of nitrification and denitrification to N2O production involves determining 15N2O isotopomers and 15N site preference (SP) via spectroscopic techniques. Using one such technique, we conducted a short-term incubation where N2O production and 15N2O isotopomers were measured 24 h after soil moisture treatments of 40 % to 105 % water-filled pore space (WFPS) were established for each of three soils that differed in nutrient levels, organic matter, and texture. Relatively low N2O fluxes and high SP values indicted nitrification during dry soil conditions, whereas at higher soil moisture, peak N2O emissions coincided with a sharp decline in SP, indicating denitrification. This pattern supports the classic N2O production curves from nitrification and denitrification as inferred by earlier research; however, our isotopomer data enabled the quantification of source partitioning for either pathway. At soil moisture levels < 53 % WFPS, the fraction of N2O attributed to nitrification (FN) predominated but thereafter decreased rapidly with increasing soil moisture (x), according to FN=3.19-0.041x, until a WFPS of 78 % was reached. Simultaneously, from WFPS of 53 % to 78 %, the fraction of N2O that was attributed to denitrification (FD) was modelled as FD=-2.19+0.041x; at moisture levels of > 78 %, denitrification completely dominated. Clearly, the soil moisture level during transition is a key regulator of N2O production pathways. The presented equations may be helpful for other researchers in estimating N2O source partitioning when soil moisture falls within the transition from nitrification to denitrification.

A review of whole farm-system analysis in evaluating greenhouse-gas mitigation strategies from livestock production systems

2018 ◽  
Vol 58 (6) ◽  
pp. 980 ◽  
Author(s):  
Richard Rawnsley ◽  
Robyn A. Dynes ◽  
Karen M. Christie ◽  
Matthew Tom Harrison ◽  
Natalie A. Doran-Browne ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Production Systems ◽  
Ghg Emissions ◽  
Livestock Production ◽  
Mitigation Strategies ◽  
System Level ◽  
Food Demand ◽  
Ghg Mitigation ◽  
Farm System ◽  
Global Food

Recognition is increasingly given to the need of improving agricultural production and efficiency to meet growing global food demand, while minimising environmental impacts. Livestock forms an important component of global food production and is a significant contributor to anthropogenic greenhouse-gas (GHG) emissions. As such, livestock production systems (LPS) are coming under increasing pressure to lower their emissions. In developed countries, LPS have been gradually reducing their emissions per unit of product (emissions intensity; EI) over time through improvements in production efficiency. However, the global challenge of reducing net emissions (NE) from livestock requires that the rate of decline in EI surpasses the productivity increases required to satisfy global food demand. Mechanistic and dynamic whole farm-system models can be used to estimate farm-gate GHG emissions and to quantify the likely changes in farm NE, EI, farm productivity and farm profitability as a result of applying various mitigation strategies. Such models are also used to understand the complex interactions at the farm-system level and to account for how component mitigation strategies perform within the complexity of these interactions, which is often overlooked when GHG mitigation research is performed only at the component level. The results of such analyses can be used in extension activities and to encourage adoption, increase awareness and in assisting policy makers. The present paper reviews how whole farm-system modelling has been used to assess GHG mitigation strategies, and the importance of understanding metrics and allocation approaches when assessing GHG emissions from LPS.

scholarly journals Denitrification in soil as a function of oxygen supply and demand at the microscale

2020 ◽  
Author(s):  
Lena Rohe ◽  
Bernd Apelt ◽  
Hans-Jörg Vogel ◽  
Reinhard Well ◽  
Gi-Mick Wu ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Water Saturation ◽  
Supply And Demand ◽  
Oxygen Demand ◽  
Aggregate Size ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
N2o Production ◽  
X Ray ◽  
O2 Supply

Abstract. The prediction of nitrous oxide (N2O) and of dinitrogen (N2) emissions formed by biotic denitrification in soil is notoriously difficult, due to challenges in capturing co-occurring processes at microscopic scales. N2O production and reduction depend on the spatial extent of anoxic conditions in soil, which in turn are a function of oxygen (O2) supply through diffusion and O2 demand by respiration in the presence of an alternative electron acceptor (e.g. nitrate). This study aimed to explore controlling factors of complete denitrification in terms of N2O and (N2O+N2) fluxes in repacked soils by taking micro-environmental conditions directly into account. This was achieved by measuring micro-scale oxygen saturation and estimating the anaerobic soil volume fraction (ansvf) based on internal air distribution measured with X-ray computed tomography (X-ray CT). O2 supply and demand was explored systemically in a full factorial design with soil organic matter (SOM, 1.2 and 4.5 %), aggregate size (2–4 and 4–8 mm) and water saturation (70, 83 and 95 % WHC) as factors. CO2 and N2O emissions were monitored with gas chromatography. The 15N gas flux method was used to estimate the N2O reduction to N2. N-gas emissions could only be predicted well, when explanatory variables for O2 supply and oxygen demand were considered jointly. Combining ansvf and CO2 emission as proxies of O2 supply and demand resulted in 83 % explained variability in (N2O+N2) emissions and together with the denitrification product ratio [N2O/(N2O+N2)] (pr) 72 % in N2O emissions. O2 concentration measured by microsensors was a poor predictor due to the variability in O2 over small distances combined with the small measurement volume of the microsensors. The substitution of predictors by independent, readily available proxies for O2 supply (diffusivity) and O2 demand (SOM) reduced the predictive power considerably (50 % and 58 % for N2O and (N2O+N2) fluxes, respectively). The new approach of using X-ray CT imaging analysis to directly quantify soil structure in terms of ansvf in combination with N2O and (N2O+N2) flux measurements opens up new perspectives to estimate complete denitrification in soil. This will also contribute to improving N2O flux models and can help to develop mitigation strategies for N2O fluxes and improve N use efficiency.

scholarly journals Emisi gas rumah kaca, cadangan karbon serta strategi adaptasi dan mitigasi pada perkebunan kopi rakyat di Nusa Tenggara Barat (Greenhouse gas emission, carbon stock, adaptation and mitigation strategies at smallholder coffee plantation in West Nusa Tenggara)

2018 ◽  
Vol 86 (2) ◽  
Author(s):  
Ali PRAMONO ◽  
. SADMAKA
Keyword(s):  
Climate Change ◽  
Carbon Stock ◽  
Ghg Emissions ◽  
Agricultural Practices ◽  
Carbon Stocks ◽  
Mitigation Strategies ◽  
Coffee Plantation ◽  
Ghg Mitigation ◽  
Coffee Plantations ◽  
Adaptation And Mitigation

Global warming and climate change are the world's major environmental, social and economic problems. The agricultural sector can act as an affected victim, greenhouse gas (GHG) contributor, and GHG absorber. Plantations have a very strategic role in the national action plan in GHG mitigation, because it has a great ability to absorb CO2. Therefore, it is necessary to determine the carbon stocks and GHG emissions from plantation management. The objectivesof the study wereto measure GHG emissions,to determine carbon stocks,and to define adaptation and mitigation strategies on climate change in existing coffee plantation systems. Gas samples were taken from 5 sampling points as replications by closedchamber method. Carbon stock estimation was done by destructive technique, including biomass of understorey and non-wood necromass. The results showed that the coffee plantations less than 10 years-oldat the study sites emitted 47 tons CO2-e/ha/year and stored carbon of 91.4 tons C/ha. Climate change adaptation strategies can be done by the application of good agricultural practices (GAP)andthe use of drought-tolerantclones, mulches,shade trees,multiple cropping systems, silt pitsand biophore techniques. The GHG mitigation can be done by the utilization of plantation waste as a source of organic fertilizer, biochar, animal feed, and bioenergy sources through the development of models of integration crop and livestock systems, as well as rejuvenation of plantation crops to increase carbon sinks and stocks.  [Keywords: climate change, carbon sequestration, coffee plantations] Abstrak Pemanasan global dan perubahan iklim menjadi masalah utama lingkungan, sosial dan ekonomi dunia hingga saat ini. Sektor pertanian dapat berperan sebagai korban terdampak, penyumbang Gas Rumah Kaca (GRK), dan penyerapGRK. Tanaman perkebunan mempunyai posisi sangat strategis dalam rencana aksi nasional di sektor pertanian, karena memiliki kemampuan besar dalam menyerap CO2. Oleh karena itu, pengukuran cadangan karbon dan emisi GRK dari pengelolaan perkebunan perlu dilakukan. Tujuan penelitian adalah untuk mengukur emisi GRK, menentukan cadangan karbon dan menetapkan strategi adaptasi dan mitigasi terhadap perubahan iklim pada sistem perkebunan kopi rakyat eksisting di Propinsi Nusa Tenggara Barat. Pengambilan contoh gas dilakukan di limatitik sampling dengan metode sungkup tertutup. Penghitungan cadangan karbon di atas permukaan tanah dilakukan dengan cara destruktifyang mencakup juga penetapan cadangan karbon biomassatanaman bawah dan biomassaserasah (ne-kromas non kayu). Hasil penelitian menunjukkan bahwa perkebunan kopi rakyat yang berumur kurang dari 10 tahun di lokasi penelitianmeng-emisikan karbon sebesar 47 ton CO2-e/ha/tahundan menyimpan cadangankarbon sebesar 91,4ton C/ha. Strategi adaptasi terhadap perubahan iklim dapat dilakukan dengan penerapan praktik Pertanian yang baik/ Good Agricultural Practices(GAP), penggunaan klon tahan kekeringan, penggunaan mulsa organik, pemanfaatanpohon penaungdan sistem tumpang sari, pembuatan rorak dan biopori.Mitigasi GRK dapat dilakukan dengan pemanfaatan limbah tanaman perkebunan sebagai sumber pupukorganik, arang (biochar), pakan ternak, dan sumber bioenergimelalui pengem-bangan model sistem integrasi tanaman dan ternak,serta peremajaan tanaman perkebunan yang sudah menurun produktivitasnya untuk meningkatkan serapan dan cadangankarbon. [Kata kunci :perubahan iklim, sekuestrasi karbon, perkebunan kopi]

scholarly journals Revisiting the relationship between soil moisture and N<sub>2</sub>O production pathways by measuring <sup>15</sup>N<sub>2</sub>O isotopomers

2019 ◽  
Author(s):  
Kate A. Congreves ◽  
Trang Phan ◽  
Richard E. Farrell
Keyword(s):  
Soil Moisture ◽  
Pore Space ◽  
Mitigation Strategies ◽  
Soil Conditions ◽  
Site Preference ◽  
N2o Emissions ◽  
Spectroscopic Techniques ◽  
N2o Production ◽  
Nitrification And Denitrification ◽  
The Relationship

Abstract. Understanding the production pathways of potent greenhouse gases, such as nitrous oxide (N2O), is essential for accurate flux prediction and for developing effective adaptation and mitigation strategies in response to climate change. Yet, there remain surprising gaps in our understanding and precise quantification of the underlying production pathways – such as the relationship between soil moisture and N2O production pathways. A powerful, but arguably underutilized, approach for quantifying the relative contribution of nitrification and denitrification to N2O production involves determining 15N2O isotopomers and 15N site preference (SP) via spectroscopic techniques. Using one such technique we conducted a short-term incubation to precisely quantify the relationship between soil moisture and N2O production pathways. For each of three soils, microcosms were arranged in a complete random design with four replicates; each microcosm consisted of air-dried soil packed into plastic petri dishes wherein moisture treatments were established for water contents equivalent to 45 to 105 % water-filled pore space (WFPS). The microcosms were placed in 1-L jars and sealed; headspace samples were collected after 24-h and analyzed for total N2O concentrations using gas chromatography, and for 15N2O isotopomers using cavity ring-down spectroscopy. Relatively low N2O fluxes and high SP values indicted nitrification during dry soil conditions, whereas at higher soil moisture, peak N2O emissions coincided with a sharp decline in SP indicating denitrification. This pattern supports the classic N2O production curves from nitrification and denitrification as inferred by earlier research; however, our isotopomer data enabled the quantification of source partitioning for either pathway thereby providing clarity on N2O sources during the transition from nitrification to denitrification. At soil moisture levels  78 %, denitrification completely dominated. Clearly, the soil moisture levels during transition is a key regulation of N2O production pathways.

scholarly journals Effectivity and Cost Efficiency of a Tax on Nitrogen Fertilizer to Reduce GHG Emissions from Agriculture

Atmosphere ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 607
Author(s):  
Andreas Meyer-Aurich ◽  
Yusuf Nadi Karatay ◽  
Ausra Nausediene ◽  
Dieter Kirschke
Keyword(s):  
Risk Aversion ◽  
Field Experiments ◽  
Function Analysis ◽  
Ghg Emissions ◽  
N Fertilizer ◽  
Relative Advantage ◽  
N2o Emissions ◽  
Ghg Mitigation ◽  
Fertilizer Use ◽  
N Fertilizer Use

The use of nitrogen (N) fertilizer substantially contributes to greenhouse gas (GHG) emissions due to N2O emissions from agricultural soils and energy-intensive fertilizer manufacturing. Thus, a reduction of mineral N fertilizer use can contribute to reduced GHG emissions. Fertilizer tax is a potential instrument to provide incentives to apply less fertilizer and contribute to the mitigation of GHG emissions. This study provides model results based on a production function analysis from field experiments in Brandenburg and Schleswig-Holstein, with respect to risk aversion by calculating certainty equivalents for different levels of risk aversion. The model results were used to identify effective and cost-efficient options considering farmers’ risk aversion to reduce N fertilizer, and to compare the potential and cost of GHG mitigation with different N fertilizer tax schemes. The results show that moderate N tax levels are effective in reducing N fertilizer levels, and thus, in curbing GHG emissions at costs below 100 €/t CO2eq for rye, barley and canola. However, in wheat production, N tax has limited effects on economically optimal N use due to the effects of N fertilizer on crop quality, which affect the sale prices of wheat. The findings indicate that the level of risk aversion does not have a consistent impact on the reduction of N fertilizer with a tax, even though the level of N fertilizer use is generally lower for risk-averse agents. The differences in N fertilizer response might have an impact on the relative advantage of different crops, which should be taken into account for an effective implementation of a tax on N fertilizer.

scholarly journals Nitrous oxide, ammonia and methane from Australian meat chicken houses measured under commercial operating conditions and with mitigation strategies applied

2016 ◽  
Vol 56 (9) ◽  
pp. 1404 ◽  
Author(s):  
S. G. Wiedemann ◽  
F. A. Phillips ◽  
T. A. Naylor ◽  
E. J. McGahan ◽  
O. B. Keane ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Nitrous Oxide ◽  
Ghg Emissions ◽  
Operating Conditions ◽  
Mitigation Strategies ◽  
N2o Emissions ◽  
Standard Diet ◽  
Litter Depth ◽  
Carbon Dioxide Equivalents ◽  
The Impact

Greenhouse gas (GHG) and ammonia emissions are important environmental impacts from meat chicken houses. This study measured ammonia (NH3), nitrous oxide (N2O) and methane (CH4) in two trials from paired, commercial meat chicken houses using standard (control) and mitigation strategies. In Trial 1, emissions from houses with standard litter depth of 47 mm (LD47) or increased litter depth of 67 mm (LD67) were compared. When standardised to a 42-day-old bird, emissions were 11.9 g NH3/bird, 0.30 g N2O/bird and 0.16 g CH4/bird from the LD47 and 11.7 g NH3/bird, 0.69 g N2O/bird and 0.12 g CH4/bird from the LD67. Emissions per kilogram of manure N were 0.14 and 0.11 for NH3-N, 0.003 and 0.005 N2O-N and CH4 conversion factors were 0.08% and 0.05%. Total direct and indirect GHG emissions reported in carbon dioxide equivalents were found to be higher in LD67 in response to the elevated direct N2O emissions. Trial 2 compared the impact of reduced crude protein (CP19.8) and a standard diet (CP21.3) developed using least-cost ration formulation, on emissions. Emissions per bird for the CP19.8 diet were 7.7 g NH3/bird, 0.39 g N2O/bird and 0.14 g CH4/bird, while emissions from birds fed the CP21.3 diet were 10.6 g NH3/bird, 0.42 g N2O/bird and 0.19 g CH4/bird. Significant differences were observed only in the NH3 results, where emissions were reduced by 27% for the low-CP diet. Because of the low emission levels, total mitigation potential from indirect GHG emissions was relatively small in Trial 2, corresponding to 11 t carbon dioxide equivalents/year per million birds.

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