Effects of integrated weed management in cropping systems on soils, microbial activity and N2O fluxes

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systems on soils, microbial activity and N2O fluxes

Anthony Vermue, Laurent Philippot, Nicolas Munier-Jolain, Florian Bizouard, David Bru, Arnaud Coffin, Catherine Hénault, Bernard Nicolardot

To cite this version:

Anthony Vermue, Laurent Philippot, Nicolas Munier-Jolain, Florian Bizouard, David Bru, et al..

Effects of integrated weed management in cropping systems on soils, microbial activity and N2O fluxes.

17. Nitrogen Workshop, Innovations for Sustainable use of Nitrogen Resources, Teagasc Agriculture

and Food Development Authority (Teagasc). IRL., Jun 2012, Wexford, Ireland. 524 p. �hal-02748195�

17 ^th

was jointly organised by

Teagasc and AFBI

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Suggested citation

Authors, 2012. Title In: Richards, K.G., Fenton, O., Watson,

C. J. (Eds). Proceedings of the 17

Nitrogen Workshop –Innovations for sustainable use of nitrogen resources. 26th – 29th June 2012, Wexford, Ireland, pp. nn-nn.

ISBN-10: 1-84170-588-8

Nitrogen

International

Workshop

The

II

Scientific Committee

KARl RIChARDS, TEAGASC OWEN FENTON, TEAGASC GARy lANIGAN, TEAGASC DAvID WAll, TEAGASC STAN lAlOR, TEAGASC

JAmES humPhREyS, TEAGASC ROGIER SChulTE, TEAGASC CAThERINE WATSON, AFBI RONNIE lAuGhlIN, AFBI JOhN BAIlEy, AFBI

Field Trip Committee

Eu DAIRymAN PROJECT: CAThAl mORAN, JAmES humPhREyS, ANDy BOlAND JOhNSTOWN CASTlE: STAN lAlOR AND GARy lANIGAN, TEAGASC

WETlANDS: RORy hARRINGTON WATERFORD COuNTy COuNCIl

CATChmENT: COlIN DONOvAN, JOE RATh AND ThE AGRICulTuRAl CATChmENTS TEAm

Acknowledgments:

We wish to thank all persons that made the 17

International Nitrogen Workshop possible. Special thanks to the organisers of the 16

Nitrogen workshop who assisted with the early planning and advised on their lessons learnt. To the invited speakers for their insightful paper contributions. To all the organisations that contributed financially to the workshop. A special word of thanks to the staff and students of Teagasc and AFBI for their valuable assistance. And finally to the participants of the Workshop for their contributions to making the 17

International Nitrogen Workshop successful.

Organising Committee

ChAIRmAN: KARl RIChARDS, TEAGASC OWEN FENTON, TEAGASC

CAThERINE WATSON, AFBI mARy FOlEy, TEAGASC JOhN BAIlEy, AFBI

NIAv mIllER, CONFERENCE ORGANISERS lTD

III

OECD Disclaimer

The opinions expressed and arguments employed in this publication are the sole

responsibility of the authors and do not necessarily reflect those of the OECD or of the governments of its member countries.

OECD CRP Accreditation

The Workshop was sponsored by the OECD Co-operative Research Programme on Biological Resource management for Sustainable Agricultural Systems, whose financial support made it possible for most of the invited speakers to participate in the Workshop.

The 17 ^th International Nitrogen Workshop is

sponsored by the OECD’s Co-operative Research

Programme on Biological Resource management

for Sustainable Agricultural Systems

IV

The following organisations have also

kindly supported the event:

V On behalf of the organising committee, it is my pleasure to welcome you to the 17^thInternational Nitrogen

Workshop “iNNovations for sustainable use of nitrogen resources”, held in the unique Wexford Opera house, Ireland from 26^thto 29^thJune 2012. The workshop is jointly organised between Teagasc (the Irish Agriculture Food and Development Authority) and AFBI (Agri-Food and Biosciences Institute, Northern Ireland).

The first Nitrogen Workshop was in 1982 at Rothamsted, u.K. as a forum for researchers to exchange ideas and views on methodologies to investigate N transformations in agricultural systems. Over the past 30 years the workshop has become an international event focusing on a wide range of nitrogen topics including improving nitrogen use efficiency and responding to policies such as the Nitrates and Water Framework Directives.

The 17^thInternational Nitrogen Workshop will focus on iNNovations for sustainable use of nitrogen resources and will cover new breakthroughs in science, knowledge transfer and management of nitrogen resources.

The workshop provides a platform to discuss the nitrogen challenges and solutions for sustainable food production and is divided into four sessions:

• Advances in understanding N-flows and Transformations

• A holistic Approach to understanding Impacts of Nitrogen on the Environment

• Global Perspectives on Nitrogen and Food Security

• Knowledge Transfer

Each of the N workshop sessions will address a central pertinent question:

• Where is the missing nitrogen?

• Which mitigation measures are synergistic/environmentally optimal?

• Will the cost of nitrogen threaten food security in the post-oil era?

• how can we bridge the gap between ever-more-detailed and narrow research and the knowledge requirements of our stakeholders?

A total of 31 oral papers and 196 poster papers are being presented at the workshop from 804 authors in 31 countries across 4 continents. The organising committee thank all authors for their written contributions to the proceedings and we look forward to your intellectual contribution through out the workshop. The financial support from all our sponsor organisations is gratefully acknowledged. We hope that you really enjoy both the Workshop and Wexford.

Karl Richards

(Chairman of the Organising Committee)

Dear Workshop Participant,

VII

TABlE OF CONTENTS

S.1.IP

Advances in Understanding N-flows

and Transformations - Invited Presentations

Advances in understanding Nitrogen Flows and Transformations – Where is

the missing Nitrogen? 2

C. Müller, T. J. Clough

Can molecular analyses provide new understanding of past, present,

and future soil nitrogen dynamics? 11

M. Firestone, S. Blazewicz, D. G. Peterson, S. Placella

S.1.OP

Advances in Understanding N-flows

and Transformations - Long Presentations

Tracing of N Transformations in Soil and Gas Phases using Isotopes and FTIR Spectroscopy 15

Soil nitrogen transformations and N2/N2O emissions after application of slurry to Irish

grassland soils, as affected by the nitrification inhibitor DCD 17

C. Watson, B. Griffiths, L. Philippot, K. Richards

The fate of urine nitrogen with use of a nitrification inhibitor 19

VIII

S.1.SP

Advances in Understanding N-flows and Transformations - Short Presentations

Search for the missing N: Excess N2 in groundwater and streams 21

Characterising dissolved organic matter flux in uK freshwaters: Sources,

Transport and Delivery 23

C. Yates, P. Johnes, R. Spencer

Investigating the efficacy of soil nitrogen tests to predict soil nitrogen supply across a range

of Irish soil types under controlled environmental conditions 25

N. McDonald, C. Watson, R. Laughlin, S. Lalor, N. Hoekstra, D. Wall

S.1.P

Advances in Understanding N-flows and Transformations - Posters

A new approach for measuring ammonia volatilization in the field: First results of the

French research project "vOlAT'Nh3" 28

J. Cohan, A. Charpiot, T. Morvan, P. Eveillard, R. Trochard, L. Champolivier, E. de Chezelles, S. Espagnol, S. Genermont, B. Loubet

Ammonia volatilization after field application of biogas residues: model based scenario

analysis of crop specific emissions 30

A. Pacholski, D. Gericke, K. Ni, H. Kage

Ammonia volatilization from banded urea: Impact of incorporation depth and

rate of application 32

P. Rochette, D. Angers, M. Chantigny, D. Pelster, N. Bertrand, M. Gasser

Ammonia volatilization from crop residues - contribution to total ammonia

volatilization at national scale 34

F. de Ruijter, J. Huijsmans

Antecedent effect of lime on denitrification in grassland soils 36

IX

Assessing N availability from municipal solid waste compost during two consecutive

lettuce cycles in Italy 38

N. Fiorentino, M. Fagnano

Assessment of the potential N mineralization/immobilization of pig slurry fractions

obtained using different techniques 40

D. Fangueiro, C. Lopes, L. Olsen, E. Vasconcelos

Biochar reduces nitrate leaching in an apple orchard 42

M. Ventura, G. Sorrenti, P. Panzacchi, G. Tonon

Can an urease inhibitor mitigate N2O and NO emissions from urea

fertilized mediterranean agrosystems? 44

A. Sanz-Cobeña, D. Abalos, T. Misselbrook, L. Garcia, A. Tellez, L. Sanchez, S. Garcia, A. Vallejo

Can arbuscular mycorrhizal fungi enhance plant nitrogen capture from

organic matter added to soil? 46

S. Saia, P. Ruisi, J. M. García-Garrido, E. Benítez, G. Amato, D. Giambalvo

Canola Response to N Fertilization as Affected by Preceding Crop and location 48

G. Lafond, E. Johnson, Y. Gan

Carbon and nitrogen residual effects after repeated manure applications 50

Comparing N recovery from legumes grown as green manures in olive orchards 52

E. Bacelar, A. Fernandes-Silva, M. Rodrigues

Comparing strategies for implementing soil organic matter and nitrogen use

in two contrasting soils 54

N. Fiorentino, C. Bertora, F. Alluvione, L. Zavattaro, M. Fagnano, F. Quaglietta Chiarandà, C. Grignani

Comparison of APSIm and DNDC for simulating nitrogen transformation and N2O

emissions from urine patches 56

I. Vogeler, R. Cichota, D. Giltrap, V. Snow

X

Determination of denitrification capacity of small headwater catchments in Flanders. 58

J. Vanderborght, J. Diels, O. Batelaan

Differentiation between fungi and bacteria as a source of N2O formation in soil 60

Do cover crops affect leaching and soil accumulation of salt and mineral N? 62

Does groundwater level determine GhGs emissions from fertilized soil? 64

Dynamic of ammonia emission from urea spreading in Po valley (Italy):

relationship with nitrogen compounds in the soil 66

M. Carozzi, R. M. Ferrara, M. Acutis, G. Rana

Dynamics of in situ nitrogen mineralization from five organic fertilizers 68

Effect of fertiliser type, rate and method of application on nitrogen leaching

in organic olive oil farming 70

B. Gómez Muñoz, R. Bol, D. J. Hatch, R. García Ruiz

Effect of long-term conservation and conventional tillage system on N2O emissions

under rainfed mediterranean agro-ecosystem. 72

A. Tellez, S. Garcia, D. Abalos, L. Sanchez, A. Sanz-Cobeña, J. L. Tenorio, A. Vallejo

Effect of N-fertilizer amount and nitrification inhibitor on N2O emissions from a

sandy and a loamy soil under vegetable production 74

P. Seiz, R. Schulz, A. Heger, M. Armbruster, F. Wiesler, T. Müller, R. Ruser

Effect of nitrogen fertilizer amount and a nitrification inhibitor on the N2O emissions

from a loamy soil cropped with winter wheat 76

I. Guzman Bustamante, R. Schulz, T. Müller, R. Hähndel, R. Ruser

Effect of soil compaction and nitrogen fertilization on nitrous oxide emission

from highly productive grassland 78

R. Loges, M. Schmeer, F. Taube

Effects of anaerobic digestion of organic manures on N turnover and N utilization 80

XI

Effects of arbuscular mycorrhizal symbiosis on the nitrogen uptake of three durum

wheat genotypes from two different organic sources 82

S. Saia, P. Ruisi, J. M. García-Garrido, G. Amato, D. Giambalvo

Effects of integrated weed management in cropping systems on soils,

microbial activity and N2O fluxes 84

A. Vermue, L. Phillippot, N. Munier-Jolain, F. Bizouard, D. Bru, A. Coffin, C. Henault, B. Nicolardot

Effects of new catch crop and tillage systems on nitrogen management in sugar

beet production 86

E. Stavridou, O. Nielsen, H. L. Kristensen

Effects of overwinter vegetation cover on soil nitrogen supply to spring barley in Ireland 88

Effects of soil inoculation with arbuscular mycorrhizal fungi on plant growth and nutrient

uptake of some mediterranean species grown under rainfed field conditions 90

Effects of storage method on N disappearance and herbage N recovery from solid

cattle manure 92

G. M. Shah, E. A. Lantinga

Effects of urea fertilization with urease and nitrification inhibitors on ammonia

volatilization and winter wheat yield 94

K. Ni, A. Pacholski, H. Kage

Efficacy of 15N nitrogen in fertilization of cereals – peas mixtures 96

Emissions of ammonia and nitrous oxide from liquid and solid fractions

of treated pig slurry 98

G. Velthof, E. Hummelink, O. Oenema

Estimating nitrate emissions to surface water: comparison of methods using detailed

regional data and national-wide databases 100

D. Rémi, C. Gascuel-Odoux, P. Durand, P. Virginie, M. Delmas, G. Deronzier, N. Domange

Evaluation of a closed tunnel for field-scale measurements of N2O fluxes at the

soil-atmosphere interface 102

K. Schäfer, J. Böttcher, D. Weymann, C. Von Der Heide, W. Duijnisveld

XII

Evaluation of nitrogen fertilisation and irrigation strategies to optimize yield, quality

and benefit in peach trees 104

J. M. Villar, M. Pascual, F. Fonseca, J. Lordan, A. Arbones, J. Rufat

Evidence of nitrate leaching hotspots over a vulnerable aquifer due to dry deposition

of ammonia from poultry houses 106

D. Seeton, S. Bittman, D. Hunt, M. Krzic, G. Kowalenko, B. Zebarth

Fertigation management of high density olive trees in calcareous soils 108

First-year's and residual herbage N recovery from fresh and composted solid cattle manures 110

Forage yield and nitrogen utilization of forage maize hybrids in Organic Farming 112

Gap filling of missing data for calculating the cumulated ammonia emission in a fertilized

bare soil: a case study in lombardia region (Italy) 114

R. M. Ferrara, M. Carozzi, M. Acutis, N. Martinelli, G. Rana

Generation of N-balances to describe N-flows and N-transformations -

The example of composting 116

K. Ina, S. Rainer

Impact of point injection of ammonium fertilizer on nitrous oxide fluxes and

nitrogen dynamics in soil 118

M. Deppe, R. Well, M. Kücke, H. Flessa

Impact of quality of residue mulches and their decomposition on N dynamics in soil

in conservation agriculture 120

S. Recous, A. Iqubal, S. Aslam, G. Alavoine, P. Benoit, P. Garnier

Impact of two different types of grassland-to-field-conversion on nitrous oxide emission

and nitrate leaching 122

R. Greta, H. Mirjam, R. Well, F. Heinz

Improving N efficiency in barley through green manure management and biogas slurry 124

Influence of fertilisation practice on gas and grain yield production 126

B. Gyarmati, E. Molnár, A. Anton, T. Szili Kovács, G. Heltai

XIII

Influence of soil amendment history on decomposition of recently applied organic

amendments 128

L. Nett, S. Ruppel, J. Ruehlmann, E. George, M. Fink

Influence of N deposition and atmospheric O3 concentration on N2O and NO

emissions from mediterranean pastures. 130

L. Sanchez, A. de La Cruz, L. Garcia, H. Calvete, H. Garcia, I. Gonzalez, V. Bermejo, A. Vallejo

Influence of soil water status and compaction on N2O and N2 emissions from

15N-labelled synthetic urine. 132

T. Harrison-Kirk, S. Thomas, M. Beare, T. Clough, T. van Der Weerden, E. Meenken

Influence of tree canopies on nitrogen dynamics in montado - a Portuguese Cork

Oak Savanna 134

D. Fangueiro, M. D. C. Caldeira, X. Lecomte, J. Coutinho

Interactions between Free-living Soil Nematodes and Ryegrass and Effects on

Nitrogen mineralization 136

M. Gebremikael, D. Buchan, S. de Neve

ley management effects on N2 fixation, crop N dynamics and residual N 138

long-term effect of a nitrification inhibitor on N2O fluxes from a loamy soil 140

maize stover incorporation increased N2O emissions twofold during a barley crop 142

malting industry effluents as a source of nitrogen to soils 144

H. Campaña, C. Cordovil, P. Benedetti, M. Uribe Etchevarría, A. Airasca, A. de Varennes

managing nitrogen losses in shallow glacial aquifers: denitrifying bioreactors as a

potential mitigation measure 146

T. Ibrahim, O. Fenton, G. Lanigan, K. Richards, M. Healy

methodology for the selection of the geographic location of new experimental sites and treatments to generate new N2O emission factors and data for model validation in the uK:

the prioritisation phase of the InveN2Ory project. 148

D. Chadwick, R. Olave, R. Laughlin, L. Cardenas, J. Williams, U. Skiba, B. Rees, S. Buckingham, K. Topp, S. Anthony

XIV

model estimation of nitrogen leaching under derogation measures on organic nitrogen

fertilization in lombardia (northern Italy) 150

A. Perego, E. Bernardoni, M. Carozzi, A. Giussani, S. Brenna, M. Acutis

modelling the effects of temporal overlap of urine patches on nitrogen leaching 152

N availability from pre-treated chicken and goat manure in an organic cropping system 154

N dynamics and priming effect in horticultural fields as influenced by application

of mineral fertilizer N 156

K. Willekens, B. Vandecasteele, S. de Neve

N fertiliser replacement value of reversed osmosis liquid fractions on arable land 158

N2O and N2 production and quantification of denitrifying populations in various

aquifer systems 160

M. Barrett, M. M. R. Jahangir

N2O emission from a maize cropping system influenced by replacing fallow with cover

crops and its subsequent incorporation into the soil. 162

S. Garcia, A. Sanz-Cobeña, J. L. Gabriel, P. Almendros, M. Quemada, A. Vallejo

Nitrate leaching after cattle slurry application to ley in autumn 164

Nitrogen dynamics in agricultural mediterranean catchments vs. temperate ones:

Ebro, Oglio, Seine and Scheldt comparisons 166

L. Lassaletta, M. Bartoli, G. Billen, J. Garnier, B. Grizzetti, E. Romero, E. Soana, P. Viaroli

Nitrogen dynamics in maize based cropping systems for biogas production 168

Nitrogen losses from buffer zones: interactions with soil structure and hydrological

pathways 170

A. Carswell, M. Blackwell, R. Bol, D. Chadwick, J. Hawkins, P. Johnes, R. Whalley

XV

Nitrogen mass balance in a coastal lowland declared vulnerable to nitrate

(WFD 2000/60/EC): the relevance of secondary canals in excess nitrogen removal 172

M. Mastrocicco, M. Bartoli

Nitrogen mineralization potential of soil amended with biochar from pig-slurry solids 174

Nitrogen mineralization potentials in rice-wheat systems in southeastern China 176

Nitrogen removal by fruits, leaves and pruning wood in a peach orchard 178

Nitrogen sources and sinks in a heavily impacted watershed (Oglio River, Northern Italy) 180

Nitrous oxide emission from biogas production systems on a coastal marsh soil 182

F. Taube, A. Herrmann

Nitrous oxide emissions during the decomposition of summer cover crop residue

under no-till 184

S. Giacomini, D. Weiler, L. Mendes Bastos, G. Dietrich, R. Schmatz, C. Aita

Nitrous oxide emissions from a clay soil under mouldboard ploughing or tine cultivation 186

J. Wetterlind, T. Rütting, L. Klemedtsson

Nitrous oxide emissions from grassland treated with different types of manure: comparison

between slurry plus fertilizer plots and farmyard manure plus fertilizer plots 188

Nitrous oxide emissions from two maizecrop seasons in northwesthern Spain 190

Optimising the spring N fertilisation rate to winter oilseed rape 192

XVI

Physicochemical changes and nitrogen losses during composting of Acacia longifolia and

Acacia melanoxylon 194

L. M. Brito, I. Mourão

Polyphenol and cellulose act as a nitrification inhibitor by different mechanisms 196

Potential for N2O emissions from volcanic grassland soils 198

L. Cardenas, D. Scholefield, D. J. Hatch, D. Jhurreea, I. Clark, P. Hirsch, F. Salazar, S. Rao-Ravella, M. Alfaro

Prediction of mineral nitrogen content in deeper layers of soil in lithuania based on its

concentration in surface layers 200

G. Staugaitis, J. Arbaciauskas, J. Mazvila, Z. Vaisvila, T. Adomaitis, L. Sasnauskaite, R. Staugaitiene, R. Mazeika

Regulatory effect of soil properties on N2O emission from wheat-growing season in five

soils: field and pot experiment 202

U. Lebender, M. Senbayram

Response of corn (Zea mays l.) to precision injected dairy slurry with focus on nitrogen 204

Role of soil organic matter content on nitrogen dynamics in volcanic ash soils 206

Seasonal variation of nitrous oxide emissions from grazed and fertilized grassland

in Galicia (Spain) 208

A. Louro López, D. Báez Bernal, M. I. García Pomar, J. Castro

Self-reseeding annual legume species as cover crops for rainfed olive orchards 210

Sensitivity of crop reflectance to crop N status of a melon crop 212

Sensitivity of the ratio leaf chlorophyll to leaf flavonoles measured with optical

sensors to crop N status of melon 214

M. T. Peña, R. Thompson, M. Gallardo, C. Gimenez

Site, preceding crop and N management effects on yield of organic winter oil seed rape 216

XVII

Soil N2O emission as affected by 3,5-Dimethilphirazolphosphate, an nitrification

inhibitor, applied on different soil types in Southern Italy 218

L. Vitale, F. Polimeno, L. Ottaiano, G. Maglione, A. Fierro, P. Di Tommasi, M. Mori, V. Magliulo

Soil Organic matter Priming: effect of labile C on N mienralisation in Irish grassland soils 220

Soil ph, and NO3- concentrations regulates the N2O and N2 emission from soil under

anoxia 222

M. Senbayram, L. R. Bakken, A. Budai, L. Marton, J. Lammel, U. Lebender

Spatiotemporal variation in groundwater nitrate-N concentrations in two agricultural

catchments 224

P. Mellander, A. Melland, P. Murphy, D. Wall, G. Shortle, P. Jordan

Strategies to reduce nitrous oxide emissions after spread of pig slurry in no-till corn

and wheat 226

C. Aita, J. Schurman, S. Giacomini, R. Gonzatto, J. Olivo, D. Giacomini

Study of the key factors which influence N2O and CO2 emissions in a fertigation

cropping system under mediterranean climate 228

D. Abalos, L. Sanchez, L. Garcia, A. Tellez, S. Garcia, A. Sanz-Cobeña, A. Vallejo

Synergetic leaching model based on pathway and pressure factors 230

Terrestrial carbon and nitrogen losses and indirect greenhouse gas emissions

via groundwater 232

M. M. R. Jahangir, P. Johnston, I. Khalil, D. Hennesey, J. Humphreys, O. Fenton, K. Richards

The complexity of the recharge processes and their effect on the seasonal variations of nitrate concentration in shallow groundwater and streams:

observations and modeling 234

L. Ruiz, P. Durand, M. Rouxel, C. Gascuel-Odoux, L. Aquilina, A. Aubert, M. Faucheux, P. Merot, J. Molenat, M. Sebilo

The effect of a mustard cover crop on groundwater denitrification 236

The effect of crop establishment system on the nitrogen use efficiency of cereal grain

crops in Ireland. 238

J. Brennan, T. McCabe, R. Hackett, P. D. Forristal

XVIII

The effect of dicyandiamide addition to cattle slurry on rates of nitrification at a grassland

site in Northern Ireland. 240

K. McGeough, C. Mueller, R. Laughlin, C. Watson, M. Ernfors, E. Cahalan, K. Richards

The effect of mineral N fertiliser dose on nitrogen efficiency of silage maize 242

The impact of crop rotation and N fertilization on the growth and yield of winter wheat 244

The interactions among the nitrogen supply and the physiological parameters and

yield of winter wheat genotypes 246

E. Szabó, P. Pepo

using bromide as tracer to study the horizontal and vertical movement of nitrate under

field conditions 248

M. Almadni, E. Stockdale, J. Cooper

Winter wheat nitrogen demand under different soil conditions 250

A. Krijger

S.2.IP

A Holistic Approach to Understanding Impacts of Nitrogen on the Environment - Invited Presentations

An integrated approach to reactive nitrogen in the environment 253

Integration of measures to mitigate reactive nitrogen loss to the environment 257

XIX

S.2.OP

A Holistic Approach to Understanding Impacts of Nitrogen on the Environment - Oral Presentations

Economic Cost of Nitrogen management 262

O. Oenema, R. D. Condor, S. Gyldenkaerne, J. Oenema

Beer, bread and other opportunities for innovation in nitrogen use 264

using NDvI to define optimal N rate: an application on durum wheat 266

S.2.SP

A Holistic Approach to Understanding Impacts of Nitrogen on the Environment - Short Presentations

Processes of nitrate-N loss to streamflow from intensive cereal crop catchments in Ireland 268

GhG balance of bioenergy cropping systems under the environmental conditions of

northern Germany 270

S. Claus, B. Wienforth, N. Svoboda, K. Sieling, H. Kage, M. Senbayram, K. Dittert, F. Taube, A. Herrmann

Animal delivery of the nitrification inhibitor DCD as a new effective method for reducing

nitrogen losses from grazed pastures 272

S. Ledgard, B. Welten, J. Luo

XX

S.2.P

A Holistic Approach to Understanding Impacts of Nitrogen on the Environment - Posters

A synergistic mitigation technology for nitrate leaching and nitrous oxide emissions

for pastoral agriculture 275

H. J. Di, K. Cameron, A. Roberts

Agricultural measures has reduced the nitrogen surplus by almost 50% in Denmark 277

Ammonia emission after on-farm application of additives in pig slurry lagoons 279

Ammonia emissions from bovine slurries during storage 281

N. Rochford, G. Lanigan, S. Lalor, K. Byrne

Ammonia volatilization losses from NBPT-treated urea stored under different conditions 283

Assessment of national scale groundwater nitrate monitoring data as a basis for

evaluating mitigation measures 285

K. Tedd, C. Coxon, D. Daly, M. Craig, B. Misstear

Bedding additives reduce ammonia emissions during storage and after application of

cattle straw manure, and improve N utilization by grassland 287

G. A. Shah, M. I. Rashid, J. C. J. Groot, P. W. G. Groot Koerkamp, E. A. Lantinga

Can leguminous crops reduce nitrous oxide emissions? 289

V. Pappa, R. Thorman, G. Bennett, B. Rees, R. Sylvester-Bradley

Characterization of indigenous rhizobial strains isolated from faba bean

(vicia faba l.) nodules 291

M. Blažinkov, S. Redžepović, N. Toth, S. Sikora, A. Stipetic

Comparison between grass, leguminous and crucifer species used as cover crops 293

Consequences of long-term application of alternative N sources on gaseous emissions. 295

P. M. Aparicio Tejo, S. Menendez

XXI

Coupling long term database with SWAT and STICS models for testing models and

simulating nitrogen management scenarios 297

D. Mathieu, P. Nicolas, J. Huguet, C. Billy, J. Duval, C. Vandenberghe, N. Beaudoin, J. M. Marcoen

Determination of nitrogen concentration in pig slurries using NIR spectroscopy 299

Differentiating sewage and manure derived nitrate within surface waters 301

Differentiation of N application standards: does it help reconcile economy and environment? 303

DmPP reduces N2O losses and maintains wheat yield under humid mediterranean

conditions 305

S. Menendez, X. Huerfano, A. Aizpurua, C. González-Murua, J. M. Estavillo

Effect of nitrogen fertilization on nitrate leaching in relation to grain yield response in

Sweden 307

S. Delin, M. Stenberg

Effect of non-fertilized winter grazing dairy production on soil N balances and soil

N dynamics in a clay-loam soil 309

M. Necpalova, P. Phelan, I. Casey, J. Humphreys

Effect of non-fertilized winter grazing dairy production system based on a clay-loam

soil on N leaching to groundwater 311

M. Necpalova, O. Fenton, I. Casey, J. Humphreys

Effect of ploughing and reseeding of permanent grassland on N leaching to groundwater

and nitrous oxide emissions from a clay-loam soil 313

M. Necpalova, I. Casey, J. Humphreys

Evaluating innovative farming systems to limit nitrogen diffuse pollution in catchments:

development and application of the CASImOD'N model 315

P. Durand, P. Moreau, C. Baratte, P. Faverdin, C. Gascuel-Odoux, E. Ramat, J. Salmon-Monviola, L. Ruiz

XXII

Factors influencing the nitrate residue levels in Flemish agricultural soils:

a statistical analysis of 8 years of nitrate measurements 317

M. Tits, A. Elsen, D. Vandervelpen, J. Bries, H. Vandendriessche, K. van Overtveld, J. Diels

Farm N balances in European landscapes and the effect of measures to reduce N-losses 319

J. Bienkowski, A. Frumau, A. Bleeker, E. Magliulo, J. E. Olesen, B. Hansen, L. Thorling, M. R. Theobald, J. L. Drouet, P. Cellier

Food-based digestate quality and fertiliser value 321

A. Rollett, M. Taylor, D. Tompkins, B. Chambers

Impact of the application of nitrogen from livestock manure on agricultural parcels on

water quality: derogation in Flanders 323

D. Vandervelpen, S. Maes, M. Tits, A. Elsen, J. Bries, H. Vandendriessche,

K. van Overtveld, L. Peeters, O. Batelaan, J. van Orshoven, J. Vanderborght, J. Diels

Impact of timing of nitrogen fertilization at tillering stage on rice plant growth in

intermittent water management. 325

M. Martinez, M. D. M. Catala-Forner, E. Pla, N. Tomas-Navarro, D. Zhu

Improvement of sensor based N application approach in winter wheat by incorporation

of soil and terrain properties 327

S. Samborski, S. Dobers, D. Gozdowski, M. Stępień

Influence of agricultural practices and climate changes in Portuguese rice production 329

P. Marques, A. Vargues

Influence of inter tillage on nitrate content in soil during tobacco crop growth 331

Irrigation and nitrogen fertiliser management effects on nitrate leaching losses from

crop rotations 333

S. Thomas, G. Francis, H. Waterland, R. Zyskowski, F. Tabley, R. Gillespie, J. Sharp, T. Fraser

mitigating ammonia emissions from stored dairy cow manure 335

T. van Der Weerden, J. Luo, M. Dexter

XXIII

modeling the effect of nitrogen management on nitrogen losses, net energy balance

and plant quality in a wheat-rapeseed rotation 337

P. Gallejones, A. Aizpurua, A. Del Prado

N fertilization and diazotrophic bacteria inoculation in sugarcane for bioenergy production 339

J. Soares, C. A. Oliveira, H. A. W. Joris, O. T. Kölln, F. L. T. Dias, S. Urquiaga

N2O emissions from Radiata Pine, Douglas fir and Beech forest stands in the Basque Country 341

Nitrate leaching to the groundwater investigated for different management practices

of organic farming and wine growing 343

F. Feichtinger, A. Scheidl

Nitrogen balances of Swiss agriculture from 1975 to 2009 344

E. Spiess

Nitrogen dynamics in soil amended with acidified and non acidified cattle slurry and

derived liquid fraction 346

D. Fangueiro, S. Surgy, J. Coutinho, F. Cabral

Nitrogen leaching and nitrous oxide emissions from grassland soils receiving dairy

soiled water 348

D. Minogue, P. French, T. Bolger, P. Murphy

Nitrogen use efficiency improvement in heavy-pig production in Northern Italy 350

Nitrogen use efficiency on dairy farms 352

E. Mihailescu, P. Murphy, I. Casey, J. Humphreys

Nitrous oxide emission determining factors for a clay soil in Sweden 354

Performance of nitrogen fertilizer rates for winter oilseed rape 356

Prediction of nitrous oxide emissions from Irish arable lands using the ECOSSE model 358

XXIV

Reducing N inputs and surpluses in baking wheat production by modifying the

valuation system – an assessment of feasibility and potential in Germany 360

Relations between management, economics and environmental quality on Dutch

arable farms 362

C. Daatselaar, H. Prins, J. Reijs

Replacing lime with gypsum as fertiliser filler in calcium ammonium nitrate (CAN):

a strategy for minimising nitrogen losses to the environment 364

J. Bailey

Response of a range of forage swards to slurry nitrogen 366

A. Dale, A. S. Laidlaw, J. S. Bailey

Temporal dynamics of soil N mineralization during an oilseed rape (Brassica napus l.)

growth cycle in one season´s growth under humid mediterranean conditions 368

The effect of measures implemented from 2003 to 2007 to reduce Nitrogen leaching

from agricultural land in Denmark 370

C. D. Børgesen, F. P. Vinther

The Environmental virtual Observatory (EvO): can cloud-based modelling provide new

understanding of nutrient cycling processes from catchment to national scale? 372

The use of Integrated Constructed Wetlands (ICW) in the management of nitrogen

(N) enriched effluents. 374

R. Harrington, P. Carroll, R. McInnes, M. Everard, C. Harrington

Tools to improve N cycle models 375

K. Betteridge, F. Li, D. C. Costall

use of a systems model to estimate the impact of management decisions on nitrate

leaching under intensive cropping 377

J. Sharp, S. Thomas, T. Fraser, H. Brown

use of chemical amendment of dairy cattle slurry to reduce phosphorus losses from dairy

cattle slurry while allowing land spreading of slurry to meet nitrogen requirements. 379

XXV

using the Eurotate_N crop model to optimize nitrogen fertilization in potato crop 381

S.3.IP

Global Perspectives on Nitrogen and Food Security - Invited Presentations

The Challenges of Feeding 9-10 Billion People - Sustainably & Equitably 384

Nitrogen and food security in the Eu from a global perspective 392

S.3.OP

Global Perspectives on Nitrogen and Food Security - Long Presentations

The Nitrogen footprint of European food production 398

J. P. Lesschen, A. Leip, S. Wagner, H. Westhoek, O. Oenema

The product carbon footprint of milk from pasture- and confinement-based dairy farming 400

S.3.SP

Global Perspectives on Nitrogen and Food Security - Short Presentations

The effect of nitrogen fertiliser application rate on nitrous oxide emission intensities

of arable crop products 402

R. Thorman, V. Pappa, K. Smith, B. Rees, M. Chauhan, G. Bennett, P. Denton, D. Munro, R. Sylvester-Bradley

XXVI

Carbon footprint of Irish milk production: can white clover make a difference? 404

Integrated assessment of nutrient management options in the food chain of China 406

S.3.P

Global Perspectives on Nitrogen and Food Security - Posters

Carbon footprint of Irish milk production 409

M. Yan, J. Humphreys, N. Holden

Effect of nitrogen fertilizer application timing on yield of winter wheat in Ireland 411

Effect of Organic and Inorganic Nitrogen fertilizer and Plant Densities on yield and

Quality of Sugar beet 413

E. Refaie, E. A. Mahmoud, M. A. Hassanin

how does sheep grazing affect the greenhouse gas balance of a grazed steppe ecosystem? 415

K. Butterbach-Bahl, A. Susenbeth, F. Taube

Influence of different nitrogen fertilizers on forage maize yield an quality 417

Nitrate metabolism in leaves of lettuce plants grown in floating system with different

nitrate concentrations 419

N. Podetta, A. Ferrante

Reducing Nitrogen in a high-Input Chinese Double-Cropping System – Effects on yield,

Soil Nitrogen and mineralisation 421

T. Hartmann, R. Schulz, T. Muller, X. P. Chen, F. S. Zhang

Soilless cultivation of vegetables in The Netherlands to reduce nitrogen emissions 423

The influence of locally injected nitrogen fertilizer (CulTAN) on seed yield of winter

rape and grain yield of spring barley in the Czech Republic 425

L. Peklova, O. Sedlar, J. Balik, O. Kozlovsky, K. Kubesova

XXVII

S.4.IP

Knowledge Transfer - Invited Presentations

Effective stakeholder communication: together we stand, divided we fall! 428

Extension & Knowledge Transfer; Effective Partnerships for Timely Impact 432

S.4.OP

Knowledge Transfer - Long Presentations

A framework for designing and evaluating nitrogen-efficient farming systems at the catchment scale by combining process studies, integrated modelling and participatory

approach. 437

P. Durand, L. Ruiz, L. Delaby, P. Moreau, L. Hubert-Moy, C. Gascuel-Odoux

Estimating the effect of mitigation methods on multiple environmental pollutants 439

M. Taylor, J. R. Williams, B. J. Chambers

S.4.SP

Knowledge Transfer - Short Presentations

Achieving good water quality status in intensive animal production areas: a lIFE+ project 441

Nitirsoil: a new N-model to estimate monthly nitrogen soil balance in irrigated agriculture. 443

Strategies to reduce N losses to water from agriculture: experiences from on-farm case

studies in the N-TOOlBOX project 445

J. Cooper, K. Gascoyne, J. Kidd, H. Kristensen, M. Maturano, M. Quemada, G. van Der Burgt

XXVIII

S.4.P

Knowledge Transfer - Posters

"Reliquat virtuel" : a new decision support tool to predict the soil inorganic N pool 448

Ammonium nutrition affects the accumulation of winter wheat glutenins 450

J. M. Estavillo, M. B. González Moro

Automating fertiliser N management 452

D. Kindred, R. Sylvester-Bradley

Comparing the efficiency of CAN, urea and urea + agrotain (n-butyl thiophosphoric

triamide) as N fertiliser in grassland 454

D. Antille, N. Hoekstra, S. Lalor

Effect of a green compost extract added to rabbit feed on nitrogen balance and ammonia

and nitrous oxide emissions from stored slurry 456

E. Dinuccio, D. Biagini, R. Rosato, P. Balsari, C. Lazzaroni, E. Montoneri

Effect of grapevine canopy management on petiole nitrogen and must amino acids

contents of dryland Chardonnay grapes 458

M. Pascual, J. M. Villar, F. Fonseca, J. Rufat, J. Lordan, J. Astrain, J. Papió

Effect of nitrogen fertilizer rate on wheat flour extensibility 460

Effect of pretreatment on estimation of slurry composition by NIR spectroscopy with

different probes 462

A. Finzi, R. Oberti, A. S. Negri, F. Perazzolo, G. Cocolo, G. Cabassi, G. Provolo

Enhanced biological nitrogen fixation in grassland swards for soil Nitrogen management 464

Fertigation techniques to increase the nitrogen use efficiency of slurries 466

Online Farm Nutrient management Calculators 468

G. Mathers, E. Chisholm, M. Browne, G. McCarney

XXIX

Plant analytical tool for nitrogen N detection status in potato crop 470

Potential indicators based on leaf flavonoids content for the evaluation of potato crop

nitrogen status 472

B. A. Feriel, G. Jean-Pierre

Quantitative evaluation of hot water extractable organic matter of organic farm soils in Japan

by measurement of chemical oxygen demand with inexpensive chemicals and equipment 474

Satellite data potential for assessing potato crop nitrogen status at a specific field scale 476

Sharing scientists' and stakeholders' knowledge in a DSS to reduce nitrogen losses in

cropping systems 478

P. Virginie, R. Reau, P. Dubrulle, C. Aubert, A. Baillet, N. Beaudoin, P. Beguin, F. Butler, P. Cannavo, J. Cohan, A. Dupont, R. Duval, S. Espagnol, J. P. Fagniez, F. Flenet, L. Fourrie, S. Genermont, L. Guichard, M. Jeuffroy, E. Justes, F. Laurent, J. MacHet, F. Maupas, T. Morvan, S. Pellerin, C. Raison, C. Raynal, S. Recous, J. Thiard

Soil quality as affected by organic and mineral N fertilization in maize 480

The rice crop response to pig slurry fertilization in Ebro Delta area (Catalonia, Spain):

four seasons studied (2008-2011). 482

M. M. Català, E. Pla, M. Martinez, N. Tomas-Navarro

using canopy reflectance to determine appropriate rate of topdress N in potatoes 484

J. N. Jukema

using data management systems to facilitate better nutrient management planning on

Irish farms 486

S. Mechan, S. Lalor, O. Shine, P. Jordan, D. Wall

Advances in Understanding Nflows and Transformations 1

Oral Presentations

SESSION

Advances in understanding nitrogen flows and transformations where is the missing nitrogen?

Müller, C.

and Clough, T.J.

aDepartment of Plant Ecology, Justus-Liebig-University Giessen, Germany

bSchool of Biology and Environmental Science, University College Dublin, Ireland

cFaculty of Agriculture and Life Sciences, Lincoln University, New Zealand

Nitrogen transformations and balances: gaps and research pathways 1. Introduction

Anthropogenically generated reactive nitrogen (N) cascades throughout the global environment (Galloway and Cowling, 2002). This reactive N may be lost from ecosystems via leaching, as nitrate (NO

), or in gaseous forms such as ammonia and nitrous oxide (N

O). These N losses are of significant importance both economically and environmentally. Despite more than 150 years of N cycling research by well known scientists such as Liebig (van der Ploeg et al., 1999), Bausingault (Aulie, 1970), Winogradsky (Ackert, 2006) and others there are still significant questions to be addressed with respect to N transformations and losses from terrestrial ecosystems.

Plant effects

Plant-soil interactions are an area of research attracting increasing interest with respect to N cycling.

They are predominantly governed by interactions between the carbon (C) and N cycles. The microbial loop in soil is driven by recent plant C inputs (e.g. rhizodeposition) which influences the microbial activity in soils and ecosystem N availability is controlled by the initial chemical composition and litter N concentrations (Manzoni et al., 2008; Parton et al., 2007). In the rhizosphere, potential N transformations such as denitrification decrease rapidly in the first few millimetres of roots (Beauchamp et al., 1989). Thus soil aggregate-microsite reactions and the influence of roots are likely to cause small-scale variations of substrate availability and environmental regulators and prompt for a diverse reaction of the microbial community (Barnard et al., 2005).

Nitrogen cycling is closely associated with plant productivity and factors affecting it. For example, conditions that favour plant C assimilation may also enhance rhizodeposition and subsequently alter microbial community composition and function with subsequent effects on N cycling. Conversely, a higher demand for N by plants, that may occur as a result of environmental change, e.g. favourable growth temperatures, increases competition for N between plants and microbes, potentially affecting microbial community structures and subsequent N transformations in the soil (Zak et al., 2003). However, only few studies have examined the links between the N cycle, plant activity and associated changes in microbial form and function that affect N transformations and fluxes. In N- limited systems, the gross N transformation rates and not the sizes of the soil N pools govern the availability of N for plants and microbes (Rastetter et al., 1997).

Plants utilise mineral N (e.g. NH

or NO

) and low molecular organic N compounds. The latter enter the soil via rhizodeposition (amino acids etc.) or are made available following microbial mineralization of organic material. Organic N (dissolved organic nitrogen, DON) uptake is reported to be more significant under conditions of N limitation and low pH (Jones et al., 2004). Despite the significance of DON as a loss pathway in agricultural ecosystems (Van Kessel et al., 2009) current knowledge of the organic N forms utilized by plants, with respect to DON dynamics over time and

2

space in the soil, and their rates of production and utilization is still limited. Similarly, the role DON plays in gaseous N loss pathways is also under researched. A recent review indicates that nitrosation reactions may be an important loss pathway for gaseous N (Spott et al., 2011).

Rhizodeposition stimulates microbial biomass growth and N turnover (Knops et al., 2002), which further stimulates the growth of predating organisms such as protozoa and nematodes (Osler and Sommerkorn, 2007; Sanderman and Amundson, 2003). Thus soil organic matter (SOM) is mineralized and decomposition of SOM may even be accelerated (priming). So far a quantitative evaluation of the various and simultaneously occurring N transformations, that lead to mineralization and immobilization of N in the rhizosphere is lacking. Can plants actively control exudation to create conditions in the rhizosphere to maximize the availability of N? Do plants actively produce compounds that deter non-beneficial organisms/pathogens directly or indirectly via relationships along trophic levels that in turn affect N cycling? Rhizodeposition of C compounds can directly influence N cycling , for instance enhancing N

O emissions in the presence of an N substrate (Uchida et al., 2011). But relatively little is known about the forms and rates of C released.

N loss from ecosystems – the importance of denitrification

A major loss pathway for N to be released into the environment is via leaching as NO

. To be rendered environmentally benign this NO

must be reduced to a non-reactive form, dinitrogen (N

).

Three major biological pathways of NO

reduction are known: i) assimilatory NO

reduction into biomass, ii) dissimilatory NO

reduction to NH

(DNRA) and iii) dissimilatory NO

reduction to N

(denitrification) (Burger and Jackson, 2004; Robertson and Kuenen, 1990). DNRA may outcompete denitrification under conditions when electron acceptors are limited and provides an energetically favourable alternative to denitrification (Rütting et al., 2011; Tiedje, 1988). However, further research is still required to understand the importance of DNRA in terrestrial systems and to perfect methods for studying the process (Rütting et al., 2011).

Denitrification is a key transformation process in soils with adverse and beneficial roles, since it impairs N use efficiency of agricultural crops, is both a source and sink for N

O, and lowers the potential for NO

leaching to aquatic systems (Davidson and Seitzinger, 2006). Denitrification is a heterotrophic process performed by facultative anaerobic organisms that utilize various C substrates as electron donors (Beauchamp et al., 1989). In aquatic systems, autotrophic denitrification may also occur in the presence of inorganic electron donors like sulphides or ferrous iron (Clément et al., 2005; Knowles, 1982).

The reductases involved in denitrification are well recognized. The membrane bound nitrate reductase (Nar) is the first in the denitrification sequence and occurs in very diverse microbial communities including a, b, g, and e proteobacteria , gram positive bacteria and archaea (Philippot, 2005) while the periplasmic NO

reductase (Nap) occurs only in gram-negative bacteria (Philippot, 2005). The key enzyme and key precursor for gaseous N emissions in the denitrification sequence is nitrite reductase which is encoded by either nirS, a cytochrome cd1 containing gene, or nirK, a copper containing gene. The two nitrite reductases provide a functional marker for the diversity of denitrifying bacteria (Braker et al., 2000). The genes norB and nosZ encode the NO and N

O reductase respectively (Groffman et al., 2006) and it is the dynamics of these two reductases in relationship to substrate and environmental regulators and in particular the balance between nar/nir and nos which controls the net production and release of N

O. Philippot et al. (Philippot et al.,

3

2011) showed that denitrifiers with and without nosZ encoding can co-exist and that higher N

O/N

ratios can be related to the proportions of bacteria with and without nosZ encoding. Differential encoding may also be related to soil pH which may differ in distinct niches (Philippot et al., 2009).

This highlights the fact that the observed overall denitrification dynamic is governed by the sum of the individual dynamics of co-existing microbes, possibly living in different niches (Philippot et al., 2011) and/or soil aggregates (Miller et al., 2009). Soil aggregate size also influences the rate of denitrification despite denitrification activity and denitrifier abundance not being associated at the aggregate level (Miller et al., 2009). Moreover, aggregation affects diffusive exchange of N

O and O

between denitrifying microsite and inter-aggregate pores, which affects both, total denitrification (Sexstone et al., 1985) and the product ratio of denitrificication (Arah and Smith, 1989).

While available organic C and oxygen have a major impact on total denitrification, soil pH influences mainly the ratio of N

O/N

(Šimek and Cooper, 2002). Maximum denitrification occurs usually at highest pH values and a linear relationship is often observed between dentrification and pH (Focht, 1974). There is a tendency that the N

O/N

ratio increases with decreasing pH (Burford and Bremner, 1975; Liu et al., 2010; Šimek and Cooper, 2002) and a more complete reduction towards N

is found at higher pH values (Nõmmik, 1956). The effect of pH may be due to an impact on substrate availability which influences membrane permeability or speciation of chemical species (Dassonville and Renault, 2002). N

O reductase is more sensitive to pH than other reductases in the denitrification sequence and therefore low pH may increase the lag phase of de novo synthesis of this enzyme (Liu et al., 2010; Šimek and Cooper, 2002). Apparently the detrimental effect of low pH on N

O reductase occurs at the post-transcriptional level by interfering with translation, protein assembly or an effect on the activity of functional enzymes (Liu et al., 2010). Microsite variations in soil pH may support a diverse microbial community which exhibits a different sensitivity to pH (Cavigelli and Robertson, 2000; Šimek and Cooper, 2002). Also chemodenitrification may play a role for N

O and N

production in acidic microsites (Chalk and Smith, 1983; Stevens et al., 1998). At pH below 3 chemical decomposition of NO

is most likely the dominant process for N

production and may account for up 50% of N losses in tropical soils (Laudelout et al., 1977). Denitrifiers adapt to low pH over long periods of time, thus experimental setups including ad hoc pH manipulations are not conducive to evaluate natural soil conditions (Šimek and Cooper, 2002).

Microbial community dynamics

Microbial community dynamics are influenced by the interacting effect of environmental conditions together with the substrate relationships (carbon substrates) and the availability of electron acceptors (N-oxides). The most important environmental regulators for denitrification are: oxygen >

pH > temperature (1974). Mineralisation activity provides substrates and is closely related to moisture/oxygen-temperature conditions (Focht and Verstraete, 1977; Morley and Baggs, 2010;

Myrold and Tiedje, 1985b). For instance a high rate of soil organic C content mineralisation favours O

consumption. In fertilized soils, C rather than NO

availability limits total denitrification, but NO

has a pronounced effect on the ratio of N

O/N

(Beauchamp et al., 1989; Dendooven and Anderson, 1994; McCarty and Bremner, 1993; Myrold and Tiedje, 1985a, b; Nõmmik, 1956). Many studies have focused on either proximal or distal factors, as described by Groffman (Groffman et al., 1988), but only a few studies so far have tried to link these factors. The C substrate determines the efficiency with which N oxides (NO

, NO

) are reduced (Beauchamp et al., 1989). Denitrifiers are able to compete successfully for C with other heterotorophs (Myrold and Tiedje, 1985b). Thus

4

specific microbe-substrate relationships exist that may explain the link between decomposition products and microbial populations (1989). However, these relationships are still not well understood. The availability and identity of the C substrates and in particular the ratio between C substrate to e

-acceptor also governs whether denitrification or DNRA occurs in soils. While the need for C is universally acknowledged there is still a need to identify assays that can predict forms of C substrate utilised by various microbial groups (Rütting et al., 2011).

Successive steps in the reductive denitrification sequence exhibit differing sensitivities to oxygen (Betlach and Tiedje, 1981). Higher N

O emissions and increasing N

O/N

ratios are observed with increasing aerobicity (Focht, 1974; Payne, 1973). Aerobic and anaerobic microsites, as indicated by different redox potentials, co-exist in soil may support different microbial communities. To advance the mechanistic understanding of microbial N cycling in terrestrial ecosystems there is a need to link microsite and not simply bulk soil conditions to microbial activities.

In natural environments diverse microbial populations are observed (Tiedje, 1988). The greatest spatial aggregation is generally observed in the top soil (Nunan et al., 2002). Spatial distributions may develop to the patchy distribution of organic material (Parkin, 1987) and in response to environmental conditions (Tiedje, 1988) such as aerobic-anaerobic microsites. There is still a need to better understand the microenvironment in where N transformations occur (McLaren, 1970).

Microbial processes are affected by substrate availability, thermodynamic regulation and inhibition, pH, and redox potential (Brock, 1967; Dassonville and Renault, 2002; Firestone and Davidson, 1989). Interactions between these factors are only poorly understood. Cavigelli and Robertson (Cavigelli and Robertson, 2000) investigated for instance the effect of pH and oxygen on the N

O/N

ratio in both an arable and a non-disturbed successional field and found that the observed differences were most likely governed by the prevailing microbial community.

New conceptual framework for N dynamics in soil

There is a need for new theoretical and conceptual frameworks to understand how microorganisms influence ecosystem processes (2011). Two aspects need to be taken into account to understand the relationships between environmental regulators and microbial activity. First, there needs to be an acknowledgement that different microsites exist in the soil, which to date have been considered as homogenous spaces with respect to environmental regulators. Secondly, there is a requirement to identify the units that represent physiologically similar microbial entities that live in mutualistic or antagonistic relationships within these microsite.

For instance while anaerobic conditions are required for denitrification to procede, aerobic denitrification (NO

reduction under microaerophyillic conditions) has been observed (Bréal, 1892). The co-respiration probably occurs under conditions when respiratory pathways are rate limited by oxygen and additional NO

reduction would allow faster growth rates (Robertson and Kuenen, 1984, 1990). Furthermore, aerobic denitrification appears to be linked to heterotrophic nitrification, and is possibly a detoxifying mechanism to reduce high NO

concentrations (Robertson and Kuenen, 1990) converted to gaseous N forms such as nitrous oxide (N

O).

Nitrous oxide is predominantly produced in soils and emitted to our atmosphere. Thus, to understand N

O production from terrestrial ecosystems it is essential to understand the potential production processes. Apart from nitrifiers und denitrifiers, N

O is also produced by nitrifiers

5