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3. Nitric oxide emissions from agricultural soils

Author

Thorman, Rachel E.

Subjects
631.4
Abstract

Nitric oxide (NO) plays a crucial role in photochemistry, particularly in the formation of tropospheric ozone. In soil the biogenic production of NO is primarily conducted by the microbial processes of nitrification and denitrification. The management of soils may, therefore, significantly impact on local atmospheric NO concentrations. The aim of this study was to investigate the influence of various agricultural practices on the magnitude of NO flux, specifically the role of tillage technique in an arable system and the comparative effect of organic wastes and inorganic fertilisers applied to a grassland system. Fluxes of NO from a sandy loam/silty clay loam soil cropped with spring barley, with and without the addition of NH4NO3 fertiliser (80 kg N ha'1), were measured using a static chamber method. The site was managed to compare the influence of 3 tillage regimes; conventional mouldboard ploughing, deep ploughing and direct drilling. There was a marked effect on the magnitude of NO fluxes fromboth the nitrogen and tillage treatment. Nitric oxide fluxes ranged between2-1deposition and emission from -2.6-49.5 jug NO-N m" h" (fertilised & ploughed) and -2.0-2.0 /xg NO-N m2 h"1 (unfertilised & direct drilled). Emissions of NO were significantly larger from the ploughed soils than from the direct drilled soils, primarily due to the increased water filled pore space stimulating denitrification and reducing NO emission. Of the fertiliser N added 0.002-0.011% was lost as NO. The flux of NO between ungrazed grassland (clay loam) and the atmosphere was measured following the application, at a target rate of 120 kg available N ha"1, of either cattle slurry, anaerobically digested sewage sludge, thermally dried sewage sludge pellets, mineral NPK fertiliser & Ficote 70? slow release fertiliser or no fertiliser addition. Nitric oxide emissions were stimulated by both organic wastes and NPK inorganic fertiliser, with cumulative fluxes markedly higher from the organic wastes, particularly from the sewage sludge pellets, which were 1.3-42.3 times larger than the other treatments. It was estimated that 0.0004-0.03% of the applied total N was released as NO. Complementary laboratory studies designed to investigate the influence of dominant environmental factors on NO emission from repacked soil cores under controlled conditions showed that NO emission was 2.2-23.5 times larger from soil amended with sewage sludge pellets. The magnitude of the flux was associated with a soil saprophytic fungus and incorporation of the pellets appeared to reduce the cumulative NO loss. In field and laboratory studies NO flux rate was strongly dependent on soil NH4+-N, soil NO3VN, soil water filled pore space and the pattern of precipitation, particularly around fertiliser application. The data suggest that NO was primarily produced by nitrification in the grassland soil and a combination of both denitrification and nitrification in the arable soil. The total flux from UK agricultural land was estimated as 0.007 Tg of NO-N. This is approximately 1.5% of the annual UK total NO-N production. Based on the evidence collected from the 2 field studies, therefore, the emission of NO from agricultural soils in the UK is not significant in terms of its contribution to the NO-N total. Flowever, agricultural soils may emit NO to the atmosphere and produce localised concentrations high enough (e.g. after fertiliser application) to generate harmful levels of tropospheric O3.

Published
2003

4. Greenhouse gas and ammonia emission mitigation priorities for UK policy targets

Author

Buckingham, Sarah, Topp, Cairistiona F.E., Smith, Pete, Eory, Vera, Chadwick, David R., Baxter, Christina K., Cloy, Joanna M., Connolly, Shaun, Cooledge, Emily C., Cowan, Nicholas J., Drewer, Julia, Duffy, Colm, Fox, Naomi J., Jebari, Asma, Jenkins, Becky, Krol, Dominika J., Marsden, Karina A., Mcauliffe, Graham A., Morrison, Steven J., O'Flaherty, Vincent, Ramsey, Rachael, Richards, Karl G., Roehe, Rainer, Smith, Jo, Smith, Kate, Takahashi, Taro, Thorman, Rachel E., Williams, John, Wiltshire, Jeremy, and Rees, Robert M.

Subjects
Agriculture and Soil Science, Atmospheric Sciences
Abstract

Agriculture is essential for providing food and maintaining food security while concurrently delivering multiple other ecosystem services. However, agricultural systems are generally a net source of greenhouse gases and ammonia. They, therefore, need to substantively contribute to climate change mitigation and net zero ambitions. It is widely acknowledged that there is a need to further reduce and mitigate emissions across sectors, including agriculture to address the climate emergency and emissions gap. This discussion paper outlines a collation of opinions from a range of experts within agricultural research and advisory roles following a greenhouse gas and ammonia emission mitigation workshop held in the UK in March 2022. The meeting identified the top mitigation priorities within the UK’s agricultural sector to achieve reductions in greenhouse gases and ammonia that are compatible with policy targets. In addition, experts provided an overview of what they believe are the key knowledge gaps, future opportunities and co-benefits to mitigation practices as well as indicating the potential barriers to uptake for mitigation scenarios discussed.

Published
2023

5. Challenges of accounting nitrous oxide emissions from agricultural crop residues

Author

Olesen, Jørgen E., Rees, Robert M., Recous, Sylvie, Bleken, Marina A., Abalos, Diego, Ahuja, Ishita, Butterbach-Bahl, Klaus, Carozzi, Marco, De Notaris, Chiara, Ernfors, Maria, Haas, Edwin, Hansen, Sissel, Janz, Baldur, Lashermes, Gwenaëlle, Massad, Raia S., Petersen, Søren O., Rittl, Tatiana F., Scheer, Clemens, Smith, Kate E., Thiébeau, Pascal, Taghizadeh-Toosi, Arezoo, Thorman, Rachel E., Topp, Cairistiona F.E., Olesen, Jørgen E., Rees, Robert M., Recous, Sylvie, Bleken, Marina A., Abalos, Diego, Ahuja, Ishita, Butterbach-Bahl, Klaus, Carozzi, Marco, De Notaris, Chiara, Ernfors, Maria, Haas, Edwin, Hansen, Sissel, Janz, Baldur, Lashermes, Gwenaëlle, Massad, Raia S., Petersen, Søren O., Rittl, Tatiana F., Scheer, Clemens, Smith, Kate E., Thiébeau, Pascal, Taghizadeh-Toosi, Arezoo, Thorman, Rachel E., and Topp, Cairistiona F.E.

Abstract

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N2O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N2O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N2O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N2O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N2O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N2O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N2O emissions.

Published
2023

6. Predicting field N2O emissions from crop residues based on their biochemical composition: A meta-analytical approach

Author

Abalos, Diego, Rittl, Tatiana, Recous, Sylvie, Thiébeau, Pascal, Topp, Cairistiona F.E., van Groenigen, Kees Jan, Butterbach-Bahl, Klaus, Thorman, Rachel E., Smith, Kate E., Ahuja, Ishita, Olesen, Jørgen E., Bleken, Marina A., Ress, Robert, Hansen, Sissel, Abalos, Diego, Rittl, Tatiana, Recous, Sylvie, Thiébeau, Pascal, Topp, Cairistiona F.E., van Groenigen, Kees Jan, Butterbach-Bahl, Klaus, Thorman, Rachel E., Smith, Kate E., Ahuja, Ishita, Olesen, Jørgen E., Bleken, Marina A., Ress, Robert, and Hansen, Sissel

Abstract

Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. How- ever, this practice often increases emissions of the powerful greenhouse gas nitrous oxide (N2O). Previous meta- analyses have linked various biochemical properties of crop residues to N2O emissions, but the relationships between these properties have been overlooked, hampering our ability to predict N2Oemissions from specific residues. Here we combine comprehensive databases for N2O emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on N2O emissions. On average, crop residue incorporation increased soil N2O emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in N2O emissions. Crop residue effects on N2O emissions were best pre- dicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and N2Oemissions differed widely in terms offormand direction. However, due to the strong correlations among these properties, wewere able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate N2O emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and lowC:N ratio) strongly stim- ulated N2O emissions, whereas mature residues with opposite characteristics had marginal effects on N2O. The most important crop types belonging to the immature residue group – cover crops, grasslands and vegetables – are important for the

Published
2022

7. Predicting field N2O emissions from crop residues based on their biochemical composition: A meta-analytical approach

Author

Abalos, Diego, primary, Rittl, Tatiana F., additional, Recous, Sylvie, additional, Thiébeau, Pascal, additional, Topp, Cairistiona F.E., additional, van Groenigen, Kees Jan, additional, Butterbach-Bahl, Klaus, additional, Thorman, Rachel E., additional, Smith, Kate E., additional, Ahuja, Ishita, additional, Olesen, Jørgen E., additional, Bleken, Marina A., additional, Rees, Robert M., additional, and Hansen, Sissel, additional

Published
2022
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8. Ammonia and nitrous oxide emission factors for excreta deposited by livestock and land‐applied manure

Author

van der Weerden, Tony J., primary, Noble, Alasdair, additional, de Klein, Cecile A. M., additional, Hutchings, Nicholas, additional, Thorman, Rachel E., additional, Alfaro, Marta A., additional, Amon, Barbara, additional, Beltran, Ignacio, additional, Grace, Peter, additional, Hassouna, Mélynda, additional, Krol, Dominika J., additional, Leytem, April B., additional, Salazar, Francisco, additional, and Velthof, Gerard L., additional

Published
2021
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9. DATAMAN : A global database of nitrous oxide and ammonia emission factors for excreta deposited by livestock and land-applied manure

Author

Beltran, Ignacio, van der Weerden, Tony J., Alfaro, Marta A., Amon, Barbara, de Klein, Cecile A.M., Grace, Peter, Hafner, Sasha, Hassouna, Mélynda, Hutchings, Nicholas, Krol, Dominika J., Leytem, April B., Noble, Alasdair, Salazar, Francisco, Thorman, Rachel E., Velthof, Gerard L., Beltran, Ignacio, van der Weerden, Tony J., Alfaro, Marta A., Amon, Barbara, de Klein, Cecile A.M., Grace, Peter, Hafner, Sasha, Hassouna, Mélynda, Hutchings, Nicholas, Krol, Dominika J., Leytem, April B., Noble, Alasdair, Salazar, Francisco, Thorman, Rachel E., and Velthof, Gerard L.

Abstract

Nitrous oxide (N2O), ammonia (NH3), and methane (CH4) emissions from the manure management chain of livestock production systems are important contributors to greenhouse gases (GHGs) and NH3 emitted by human activities. Several studies have evaluated manure-related emissions and associated key variables at regional, national, or continental scales. However, there have been few studies focusing on the drivers of these emissions using a global dataset. An international project was created (DATAMAN) to develop a global database on GHG and NH3 emissions from the manure management chain (housing, storage, and field) to identify key variables influencing emissions and ultimately to refine emission factors (EFs) for future national GHG inventories and NH3 emission reporting. This paper describes the “field” database that focuses on N2O and NH3 EFs from land-applied manure and excreta deposited by grazing livestock. We collated relevant information (EFs, manure characteristics, soil properties, and climatic conditions) from published peer-reviewed research, conference papers, and existing databases. The database, containing 5,632 observations compiled from 184 studies, was relatively evenly split between N2O and NH3 (56 and 44% of the EF values, respectively). The N2O data were derived from studies conducted in 21 countries on five continents, with New Zealand, the United Kingdom, Kenya, and Brazil representing 86% of the data. The NH3 data originated from studies conducted in 17 countries on four continents, with the United Kingdom, Denmark, Canada, and The Netherlands representing 79% of the data. Wet temperate climates represented 90% of the total database. The DATAMAN field database is available at http://www.dataman.co.nz.

Published
2021

10. Ammonia and nitrous oxide emission factors for excreta deposited by livestock and land-applied manure

Author

van der Weerden, Tony J., Noble, Alasdair, de Klein, Cecile A.M., Hutchings, Nicholas, Thorman, Rachel E., Alfaro, Marta A., Amon, Barbara, Beltran, Ignacio, Grace, Peter, Hassouna, Mélynda, Krol, Dominika J., Leytem, April B., Salazar, Francisco, Velthof, Gerard L., van der Weerden, Tony J., Noble, Alasdair, de Klein, Cecile A.M., Hutchings, Nicholas, Thorman, Rachel E., Alfaro, Marta A., Amon, Barbara, Beltran, Ignacio, Grace, Peter, Hassouna, Mélynda, Krol, Dominika J., Leytem, April B., Salazar, Francisco, and Velthof, Gerard L.

Abstract

Manure application to land and deposition of urine and dung by grazing animals are major sources of ammonia (NH3) and nitrous oxide (N2O) emissions. Using data on NH3 and N2O emissions following land-applied manures and excreta deposited during grazing, emission factors (EFs) disaggregated by climate zone were developed, and the effects of mitigation strategies were evaluated. The NH3 data represent emissions from cattle and swine manures in temperate wet climates, and the N2O data include cattle, sheep, and swine manure emissions in temperate wet/dry and tropical wet/dry climates. The NH3 EFs for broadcast cattle solid manure and slurry were 0.03 and 0.24 kg NH3–N kg–1 total N (TN), respectively, whereas the NH3 EF of broadcast swine slurry was 0.29. Emissions from both cattle and swine slurry were reduced between 46 and 62% with low-emissions application methods. Land application of cattle and swine manure in wet climates had EFs of 0.005 and 0.011 kg N2O–N kg–1 TN, respectively, whereas in dry climates the EF for cattle manure was 0.0031. The N2O EFs for cattle urine and dung in wet climates were 0.0095 and 0.002 kg N2O–N kg–1 TN, respectively, which were three times greater than for dry climates. The N2O EFs for sheep urine and dung in wet climates were 0.0043 and 0.0005, respectively. The use of nitrification inhibitors reduced emissions in swine manure, cattle urine/dung, and sheep urine by 45–63%. These enhanced EFs can improve national inventories; however, more data from poorly represented regions (e.g., Asia, Africa, South America) are needed.

Published
2021

12. DATAMAN: A global database of nitrous oxide and ammonia emission factors for excreta deposited by livestock and land‐applied manure

Author

Beltran, Ignacio, primary, van der Weerden, Tony J., additional, Alfaro, Marta A., additional, Amon, Barbara, additional, de Klein, Cecile A. M., additional, Grace, Peter, additional, Hafner, Sasha, additional, Hassouna, Mélynda, additional, Hutchings, Nicholas, additional, Krol, Dominika J., additional, Leytem, April B., additional, Noble, Alasdair, additional, Salazar, Francisco, additional, Thorman, Rachel E., additional, and Velthof, Gerard L., additional

Published
2021
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15. Towards Country-Specific Nitrous Oxide Emission Factors for Manures Applied to Arable and Grassland Soils in the UK

Author

Thorman, Rachel E., primary, Nicholson, Fiona A., additional, Topp, Cairistiona F. E., additional, Bell, Madeleine J., additional, Cardenas, Laura M., additional, Chadwick, David R., additional, Cloy, Joanna M., additional, Misselbrook, Tom H., additional, Rees, Robert M., additional, Watson, Catherine J., additional, and Williams, John R., additional

Published
2020
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19. Ammonia and nitrous oxide emission factors for excreta deposited by livestock and land‐applied manure

Author

Weerden, Tony J., Noble, Alasdair, Klein, Cecile A. M., Hutchings, Nicholas, Thorman, Rachel E., Alfaro, Marta A., Amon, Barbara, Beltran, Ignacio, Grace, Peter, Hassouna, Mélynda, Krol, Dominika J., Leytem, April B., Salazar, Francisco, and Velthof, Gerard L.

Abstract

Manure application to land and deposition of urine and dung by grazing animals are major sources of ammonia (NH3) and nitrous oxide (N2O) emissions. Using data on NH3and N2O emissions following land‐applied manures and excreta deposited during grazing, emission factors (EFs) disaggregated by climate zone were developed, and the effects of mitigation strategies were evaluated. The NH3data represent emissions from cattle and swine manures in temperate wet climates, and the N2O data include cattle, sheep, and swine manure emissions in temperate wet/dry and tropical wet/dry climates. The NH3EFs for broadcast cattle solid manure and slurry were 0.03 and 0.24 kg NH3–N kg–1total N (TN), respectively, whereas the NH3EF of broadcast swine slurry was 0.29. Emissions from both cattle and swine slurry were reduced between 46 and 62% with low‐emissions application methods. Land application of cattle and swine manure in wet climates had EFs of 0.005 and 0.011 kg N2O–N kg–1TN, respectively, whereas in dry climates the EF for cattle manure was 0.0031. The N2O EFs for cattle urine and dung in wet climates were 0.0095 and 0.002 kg N2O–N kg–1TN, respectively, which were three times greater than for dry climates. The N2O EFs for sheep urine and dung in wet climates were 0.0043 and 0.0005, respectively. The use of nitrification inhibitors reduced emissions in swine manure, cattle urine/dung, and sheep urine by 45–63%. These enhanced EFs can improve national inventories; however, more data from poorly represented regions (e.g., Asia, Africa, South America) are needed.

Published
2021
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22. Global Research Alliance N2O chamber methodology guidelines: Design considerations

Author

Clough, Timothy J., Rochette, Philippe, Thomas, Steve M., Pihlatie, Mari, Christiansen, Jesper R., and Thorman, Rachel E.

Abstract

Terrestrial ecosystems, both natural ecosystems and agroecosystems, generate greenhouse gases (GHGs). The chamber method is the most common method to quantify GHG fluxes from soil–plant systems and to better understand factors affecting their generation and mitigation. The objective of this study was to review and synthesize literature on chamber designs (non‐flow‐through, non‐steady‐state chamber) and associated factors that affect GHG nitrous oxide (N2O) flux measurement when using chamber methods. Chamber design requires consideration of many facets that include materials, insulation, sealing, venting, depth of placement, and the need to maintain plant growth and activity. Final designs should be tailored, and bench tested, in order to meet the nuances of the experimental objectives and the ecosystem under study while reducing potential artifacts. Good insulation, to prevent temperature fluctuations and pressure changes, and a high‐quality seal between base and chamber are essential. Elimination of pressure differentials between headspace and atmosphere through venting should be performed, and designs now exist to eliminate Venturi effects of earlier tube‐type vent designs. The use of fans within the chamber headspace increases measurement precision but may alter the flux. To establish best practice recommendations when using fans, further data are required, particularly in systems containing tall plants, to systematically evaluate the effects that fan speed, position, and mixing rate have on soil gas flux.

Published
2020
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23. Global Research Alliance N2O chamber methodology guidelines: Recommendations for deployment and accounting for sources of variability

Author

Charteris, Alice F., Chadwick, David R., Thorman, Rachel E., Vallejo, Antonio, Klein, Cecile A.M., Rochette, Philippe, and Cárdenas, Laura M.

Abstract

Adequately estimating soil nitrous oxide (N2O) emissions using static chambers is challenging due to the high spatial variability and episodic nature of these fluxes. We discuss how to design experiments using static chambers to better account for this variability and reduce the uncertainty of N2O emission estimates. This paper is part of a series, each discussing different facets of N2O chamber methodology. Aspects of experimental design and sampling affected by spatial variability include site selection and chamber layout, size, and areal coverage. Where used, treatment application adds a further level of spatial variability. Time of day, frequency, and duration of sampling (both individual chamber closure and overall experiment duration) affect the temporal variability captured. We also present best practice recommendations for chamber installation and sampling protocols to reduce further uncertainty. To obtain the best N2O emission estimates, resources should be allocated to minimize the overall uncertainty in line with experiment objectives. Sometimes this will mean prioritizing individual flux measurements and increasing their accuracy and precision by, for example, collecting four or more headspace samples during each chamber closure. However, where N2O fluxes are exceptionally spatially variable (e.g., in heterogeneous agricultural landscapes, such as uneven and woody grazed pastures), using available resources to deploy more chambers with fewer headspace samples per chamber may be beneficial. Similarly, for particularly episodic N2O fluxes, generated for example by irrigation or freeze–thaw cycles, increasing chamber sampling frequency will improve the accuracy and reduce the uncertainty of temporally interpolated N2O fluxes.

Published
2020
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24. Effects of the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on gross N transformation rates and N2O emissions.

Author

Zhu, Gaodi, Ju, Xiaotang, Zhang, Jinbo, Müller, Christoph, Rees, Robert M, Thorman, Rachel E., and Sylvester-Bradley, Roger

Subjects
NITRIFICATION inhibitors, NITROUS oxide, SOIL absorption & adsorption, HISTOSOLS, NITRIFICATION, PHOSPHATES, CLAY
Abstract

Many studies have shown the efficiency of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) in suppressing nitrification and nitrous oxide (N2O) emissions. However, the effect of DMPP on soil gross nitrogen transformations and the mechanism of its inhibitory effects on N2O production pathways remain unknown. A 15N tracing experiment was conducted to investigate the effect of DMPP on gross N transformation rates and pathways of N2O production in two typical Chinese and UK agricultural soils. The soils differed in organic carbon (C) and clay content but otherwise had similar properties. The results showed that the application of DMPP decreased the gross autotrophic nitrification rate (p < 0.05) by 21.6% in the Chinese soil and 9.4% in the UK soil. The lower inhibitory efficiency of DMPP in the UK soil was likely to have been due to high rates of adsorption by soil organic C and clay. The total gross rate of mineralization was lower in the presence of DMPP in both soils, likely because there was a regulatory feedback when ammonium concentrations were high. DMPP also significantly reduced cumulative N2O emissions (p < 0.05) in both soils (by between 15.8 and 68.4%), which might be attributed to the dual inhibitory effect of the DMPP on autotrophic nitrification rate and the proportion of N2O produced by autotrophic nitrification processes. This finding will help to predict the sites where DMPP is likely to be most effective and allow the user to target DMPP application to soils with particular properties. [ABSTRACT FROM AUTHOR]

Published
2019
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26. Nitrous oxide mitigation in UK agriculture

Author

Rees, Robert M., primary, Baddeley, John A., additional, Bhogal, Anne, additional, Ball, Bruce C., additional, Chadwick, David R., additional, Macleod, Michael, additional, Lilly, Allan, additional, Pappa, Valentini A., additional, Thorman, Rachel E., additional, Watson, Christine A., additional, and Williams, John R., additional

Published
2013
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28. Challenges of accounting nitrous oxide emissions from agricultural crop residues.

Author

Olesen JE, Rees RM, Recous S, Bleken MA, Abalos D, Ahuja I, Butterbach-Bahl K, Carozzi M, De Notaris C, Ernfors M, Haas E, Hansen S, Janz B, Lashermes G, Massad RS, Petersen SO, Rittl TF, Scheer C, Smith KE, Thiébeau P, Taghizadeh-Toosi A, Thorman RE, and Topp CFE

Subjects
Soil chemistry, Poaceae, Biomass, Nitrogen analysis, Agriculture, Fertilizers, Crops, Agricultural, Nitrous Oxide analysis
Abstract

Crop residues are important inputs of carbon (C) and nitrogen (N) to soils and thus directly and indirectly affect nitrous oxide (N 2 O) emissions. As the current inventory methodology considers N inputs by crop residues as the sole determining factor for N 2 O emissions, it fails to consider other underlying factors and processes. There is compelling evidence that emissions vary greatly between residues with different biochemical and physical characteristics, with the concentrations of mineralizable N and decomposable C in the residue biomass both enhancing the soil N 2 O production potential. High concentrations of these components are associated with immature residues (e.g., cover crops, grass, legumes, and vegetables) as opposed to mature residues (e.g., straw). A more accurate estimation of the short-term (months) effects of the crop residues on N 2 O could involve distinguishing mature and immature crop residues with distinctly different emission factors. The medium-term (years) and long-term (decades) effects relate to the effects of residue management on soil N fertility and soil physical and chemical properties, considering that these are affected by local climatic and soil conditions as well as land use and management. More targeted mitigation efforts for N 2 O emissions, after addition of crop residues to the soil, are urgently needed and require an improved methodology for emission accounting. This work needs to be underpinned by research to (1) develop and validate N 2 O emission factors for mature and immature crop residues, (2) assess emissions from belowground residues of terminated crops, (3) improve activity data on management of different residue types, in particular immature residues, and (4) evaluate long-term effects of residue addition on N 2 O emissions., (© 2023 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Published
2023
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29. Predicting field N 2 O emissions from crop residues based on their biochemical composition: A meta-analytical approach.

Author

Abalos D, Rittl TF, Recous S, Thiébeau P, Topp CFE, van Groenigen KJ, Butterbach-Bahl K, Thorman RE, Smith KE, Ahuja I, Olesen JE, Bleken MA, Rees RM, and Hansen S

Subjects
Agriculture, Crops, Agricultural, Fertilizers, Soil, Ecosystem, Nitrous Oxide analysis
Abstract

Crop residue incorporation is a common practice to increase or restore organic matter stocks in agricultural soils. However, this practice often increases emissions of the powerful greenhouse gas nitrous oxide (N 2 O). Previous meta-analyses have linked various biochemical properties of crop residues to N 2 O emissions, but the relationships between these properties have been overlooked, hampering our ability to predict N 2 O emissions from specific residues. Here we combine comprehensive databases for N 2 O emissions from crop residues and crop residue biochemical characteristics with a random-meta-forest approach, to develop a predictive framework of crop residue effects on N 2 O emissions. On average, crop residue incorporation increased soil N 2 O emissions by 43% compared to residue removal, however crop residues led to both increases and reductions in N 2 O emissions. Crop residue effects on N 2 O emissions were best predicted by easily degradable fractions (i.e. water soluble carbon, soluble Van Soest fraction (NDS)), structural fractions and N returned with crop residues. The relationship between these biochemical properties and N 2 O emissions differed widely in terms of form and direction. However, due to the strong correlations among these properties, we were able to develop a simplified classification for crop residues based on the stage of physiological maturity of the plant at which the residue was generated. This maturity criteria provided the most robust and yet simple approach to categorize crop residues according to their potential to regulate N 2 O emissions. Immature residues (high water soluble carbon, soluble NDS and total N concentration, low relative cellulose, hemicellulose, lignin fractions, and low C:N ratio) strongly stimulated N 2 O emissions, whereas mature residues with opposite characteristics had marginal effects on N 2 O. The most important crop types belonging to the immature residue group - cover crops, grasslands and vegetables - are important for the delivery of multiple ecosystem services. Thus, these residues should be managed properly to avoid their potentially high N 2 O emissions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Published
2022
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30. Gross N transformation rates and related N 2 O emissions in Chinese and UK agricultural soils.

Author

Zhu G, Song X, Ju X, Zhang J, Müller C, Sylvester-Bradley R, Thorman RE, Bingham I, and Rees RM

Subjects
Agriculture, China, England, Scotland, Denitrification, Nitrification, Nitrogen chemistry, Nitrous Oxide analysis, Soil chemistry
Abstract

The properties of agricultural soils in various regions of the world are variable and can have a significant but poorly understood impact on soil nitrogen (N) transformations and nitrous oxide (N 2 O) emissions. For this reason, we undertook a study of gross N transformations and related N 2 O emissions in contrasting agricultural soils from China and the UK. Seven Chinese and three UK agricultural soils were collected for study using a 15 N tracing approach. The soil pH ranged from 5.4 to 8.7, with three acidic soils collected from Jinjing, Lishu and Boghall; one neutral soil collected from Changshu, and the other six alkaline soils collected from Quzhou, Zhangye, Changwu, Jinzhong, Boxworth and Stetchworth. Our results showed that the main N transformation processes were oxidation of ammonium (NH 4 + ) to nitrate (NO 3 - ) (O NH4 ), and mineralization of organic N to NH 4 + . The gross autotrophic nitrification rates calculated in the three acidic soils were between 0.25 and 4.15 mg N kg -1  d -1 , which were significantly lower (p < 0.05) than those in the remaining neutral and alkaline soils ranging from 6.94 to 14.43 mg N kg -1  d -1 . Generally, soil pH was positively correlated (p < 0.001) with gross autotrophic nitrification rate and cumulative N 2 O emissions, indicating that soil pH was an important factor regulating autotrophic nitrification and N 2 O emissions. There was also a significant positive correlation between the gross autotrophic nitrification rate and cumulative N 2 O emissions, highlighting the importance of this process for producing N 2 O emissions in these agricultural soils under aerobic conditions. Gross NH 4 + immobilization rates were very low in most soils except for the Jinjing soil with the lowest pH. In conclusion, the gross autotrophic nitrification rates and related N 2 O emissions were controlled by soil pH irrespectively of the soil's origin in these agricultural soils., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Published
2019
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