# Nitrogen Opportunities for Agriculture, Food & Environment

UNECE Guidance Document on Integrated Sustainable Nitrogen Management

<figure><img src="image_1.png" /></figure>
Published by the UK Centre for Ecology & Hydrology (UKCEH), Edinburgh
UK, on behalf of Task Force on Reactive Nitrogen, of the UNECE Convention
on Long-range Transboundary Air Pollution.

ISBN: 978-1-906698-78-2

© UK Centre for Ecology & Hydrology, 2022.

This publication is in copyright. It may be quoted and graphics reproduced
subject to appropriate citation.

**Recommended citation**

Sutton, M. A., Howard, C. M., Mason, K. E., Brownlie, W. J., Cordovil, C. M. d. S. (eds.), 2022. *Nitrogen Opportunities for Agriculture, Food & Environment*. UNECE Guidance Document on Integrated Sustainable Nitrogen Management. UK Centre for Ecology & Hydrology, Edinburgh, UK.

INMS Report 2022/02

This book is the published version of the UNECE Guidance Document on Integrated Sustainable Nitrogen Management (ECE/EB.AIR/149), as adopted by the Executive Body of the Convention on Long-range Transboundary Air Pollution (the Geneva Air Convention), at its 40th session (18th December 2020), together with additional images for which © is as indicated.

The Guidance Document on Integrated Sustainable Nitrogen Management was prepared by the Task Force on Reactive Nitrogen in accordance with item 2.2.3 of the 2020–2021 workplan for the implementation of the Convention (ECE/EB.AIR/144/Add.2). The long-term strategy for the Convention for 2020–2030 and beyond (ECE/EB.AIR/142/Add.2, decision 2018/5) recognized the disruption of the nitrogen cycle as one of the most important challenges for environmental policy that required an integrated approach (paras. 68 and 79 (d)). The purpose of the document is to mobilize Parties’ efforts to control pollution from agricultural sources in the context of the wider nitrogen cycle in an integrated manner harvesting multiple co-benefits of improved nitrogen management. The document is in particular aimed to support the implementation of the Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-level Ozone. The work was completed before 24th February 2022.

**Disclaimer**

The designations employed and the presentation of the material in this publication
do not imply the expression of any opinion whatsoever on the part of the
Secretariat of the United Nations concerning the legal status of any country,
territory, city or area, or of its authorities, or concerning the delimitation of its
frontiers or boundaries.

**Acknowledgements**

Meetings, preparation and publication of the Guidance Document were
kindly supported by contributions from the European Commission, the Global
Environment Facility (GEF) through the United Nations Environment Programme
(UNEP) project "Towards the International Nitrogen Management System" (INMS),
the UK Centre for Ecology & Hydrology and the UK Department for Environment
Food and Rural Affairs (Defra). The contribution of many authors and experts to the
Brussels workshops in 2016/2019 and to the chapters is gratefully acknowledged.
We thank all the experts attending workshops and contributing comments on the
draft text, as listed at the end of this document (Appendix III).

**Cover photo**

On-farm use of trailing hose technique (Field Measure 6) to reduce ammonia emissions in a sensitive landscape. For optimal performance, hose exits should be set within 15 cm of the ground, though may be raised when turning and transporting manure to fields.

© L'Albeitar, 2021.
# Nitrogen Opportunities for Agriculture, Food & Environment

## UNECE Guidance Document on Integrated Sustainable Nitrogen Management

Edited by

M.A. Sutton, C.M. Howard, K.E. Mason, W.J. Brownlie & C. M. d. S. Cordovil

<figure><img src="image_2.png" /></figure>

UNECE

<figure><img src="image_3.png" /></figure>

Task
Force on
Reactive
Nitrogen

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

INMS

UNECE Convention on Long-range Transboundary Air Pollution,
with support from GEF/UNEP International Nitrogen Management System.
Foreword

With the establishment of the Task Force on Reactive Nitrogen in 2007, the UNECE Convention on Long-range Transboundary Air Pollution (informally the Air Convention) took an important step in embracing the challenge that control of air pollution is linked to many other transboundary and global challenges. This interconnected reality is no more apparent than with human disturbance of the nitrogen cycle, which links food and energy production with pollution of air, soil and water, human health, climate change and biodiversity loss.

The mandate given by the Executive Body of the Convention (ECE/EB.AIR/91/Add.1, decision 2007/1) clearly recognized this perspective, establishing the Task Force "with the long-term goal of developing technical and scientific information, and options which can be used for strategy development across the UNECE to encourage coordination of air pollution policies on nitrogen in the context of the nitrogen cycle and which may be used by other bodies outside the Convention in consideration of other control measures". In this way, the Convention fully appreciated that sustainable nitrogen management not only benefits air, but also helps many other aspects of sustainable development.

The present document has been prepared by the Task Force on Reactive Nitrogen with exactly this philosophy in mind. With a focus on agriculture and food in the wider environment, the document identifies principles and measures for integrated sustainable nitrogen management, with a view toward harvesting multiple simultaneous benefits. The document builds on the existing UNECE Guidance Document on preventing and abating ammonia emissions from agricultural sources (Ammonia Guidance Document, ECE/EB.AIR/120) and the UNECE Framework Code for Good Agricultural Practice for Reducing Ammonia Emissions (Ammonia Framework Code, ECE/EB.AIR/129). These documents still stand: the first as the definitive reference on ammonia abatement and the second as a practical guide to help Parties establish their own National Ammonia Codes, as required under Annex IX of the Gothenburg Protocol.

What was missing was a document to guide Parties and other stakeholders in how to reduce multiple forms of nitrogen loss simultaneously. Apart from ammonia (NH₃), this has meant considering emissions of nitrogen oxides (NOx) and nitrous oxide (N₂O) to air, alongside nitrate (NO₃⁻) and other reactive nitrogen (N₂) losses to water. In addition, it is now recognized that, while denitrification of Nₐ to atmospheric di-nitrogen (N₂) does not cause pollution directly, it represents a waste of valuable Nₐ resources, reducing nitrogen use efficiency across the economy. This in turn requires more new Nₐ inputs (such as from fertilizer and biological nitrogen fixation), ultimately increasing nitrogen pollution. Just as the Colombo Declaration has identified the ambition to "halve nitrogen waste" from all sources, it means that there is a need for guidance on principles and measures to help reduce all nitrogen losses.

The engagement through the Air Convention is already forcing us to change our thinking. In the past, we mainly focused on individual nitrogen pollutants, with a fragmented approach across nitrogen issues. At the same time, society has encountered major barriers-to-change to reducing nitrogen emissions. Under the emerging 'joined-up' approach to nitrogen, we realise that the synergies are critical, since they provide win-wins that can help mobilize action. By reducing all nitrogen losses, there is the opportunity not just for cleaner air and water, and for reducing climate change and stratospheric ozone depletion, but simultaneous co-benefits for health, ecosystems and circular economy. With around $200 billion worth of Nₐ resources wasted annually to air, land and water, it highlights a $100 billion per year opportunity from halving all nitrogen waste, gaseous, aqueous and solid (i.e., the sum of all N losses including denitrification to N₂).

We hope that the present document can be useful to inform the present review of the UNECE Gothenburg Protocol and the eventual revision of air pollution policies beyond 2030. At the same time, this guidance can support the goals of multiple UN conventions, including on climate, biodiversity, water, stratospheric ozone etc. In this regard, the UNECE experience is already providing useful lessons as GEF/UNEP develop the International Nitrogen Management System (INMS) and an intergovernmental mechanism for coordination of nitrogen policies, with the UNECE Air Convention playing a key role in leading the way.

**Mark Sutton, Cláudia Cordovil, Tommy Dalgaard**
*Co-chairs UNECE Task Force on Reactive Nitrogen*

**Clare Howard and Nicole Read**
*Task Force on Reactive Nitrogen Coordination Team*
Acronyms

<table><tr><td>AE</td><td>Abatement Efficiency</td></tr><tr><td>AN</td><td>Ammonium Nitrate</td></tr><tr><td>BAT</td><td>Best Available Technique</td></tr><tr><td>BMP</td><td>Best Management Practices</td></tr><tr><td>BSP</td><td>Best System Practices</td></tr><tr><td>C</td><td>Carbon</td></tr><tr><td>C/N</td><td>Carbon-to-Nitrogen ratio</td></tr><tr><td>CAN</td><td>Calcium Ammonium Nitrate</td></tr><tr><td>CBA</td><td>Cost-Benefit Analysis</td></tr><tr><td>CDU</td><td>Crotonylidene diurea</td></tr><tr><td>CH<sub>4</sub></td><td>Methane</td></tr><tr><td>CLRTAP</td><td>UNECE Convention on Long-range Transboundary Air Pollution (informally the "Air Convention")</td></tr><tr><td>CO<sub>2</sub></td><td>Carbon dioxide</td></tr><tr><td>CP</td><td>Crude Protein</td></tr><tr><td>DCD</td><td>Dicyandiamide - a nitrification inhibitor</td></tr><tr><td>DM</td><td>Dry Matter</td></tr><tr><td>DMPP</td><td>3,4-dimethylpyrazole phosphate - a nitrification inhibitor</td></tr><tr><td>DOC</td><td>Dissolved Organic Carbon</td></tr><tr><td>DON</td><td>Dissolved Organic Nitrogen</td></tr><tr><td>DPSIR</td><td>Driver-Pressure-State-Impact-Response</td></tr><tr><td>ECE</td><td>United Nations Economic Commission for Europe</td></tr><tr><td>ENA</td><td>European Nitrogen Assessment</td></tr><tr><td>EU</td><td>European Union</td></tr><tr><td>EU28</td><td>The former group of 28 countries of the European Union, now EU27</td></tr><tr><td>FAO</td><td>Food and Agriculture Organization of the United Nations</td></tr><tr><td>FYM</td><td>Farmyard Manure</td></tr><tr><td>GEF</td><td>Global Environment Facility</td></tr><tr><td>GHG</td><td>Greenhouse Gas</td></tr><tr><td>GPS</td><td>Global Positioning System</td></tr><tr><td>H<sub>2</sub>O</td><td>Water</td></tr><tr><td>HELCOM</td><td>Helsinki Commission for Baltic Marine Environment Protection</td></tr><tr><td>HNO<sub>3</sub></td><td>Nitric acid</td></tr><tr><td>IBDU</td><td>Isobutylidene diurea</td></tr><tr><td>INCOM</td><td>Inter-convention Nitrogen Coordination Mechanism</td></tr><tr><td>INMS</td><td>International Nitrogen Management System - implemented through the GEF/United Nations Environment Programme Towards INMS project</td></tr><tr><td>IPCC</td><td>Intergovernmental Panel on Climate Change</td></tr><tr><td>K</td><td>Potassium</td></tr><tr><td>LRTAP</td><td>UNECE Convention on Long-range Transboundary Air Pollution (informally the "Air Convention")</td></tr><tr><td>N</td><td>Nitrogen</td></tr><tr><td>N footprint</td><td>Nitrogen footprint</td></tr><tr><td>N<sub>2</sub></td><td>Dinitrogen - a colourless and odourless gas, forming about 78 per cent of the Earth's atmosphere</td></tr><tr><td>N<sub>2</sub>O</td><td>Nitrous oxide - a powerful greenhouse gas</td></tr><tr><td>NAC</td><td>National Ammonia Code</td></tr><tr><td>NBPT</td><td>N-(n-butyl) thiophosphoric triamide - a urease inhibitor</td></tr><tr><td>NGO</td><td>Non-governmental organization</td></tr><tr><td>NH<sub>3</sub></td><td>Ammonia - an air and water pollutant and the primary nitrogen form in biological systems</td></tr></table>
<table>
   <tr>
    <td>NH<sub>4</sub><sup>+</sup></td>
    <td>Ammonium – present in biological systems and soils, while forming a pollutant in atmospheric PM and aquatic systems</td>
   </tr>
   <tr>
    <td>NH<sub>x</sub></td>
    <td>Total ammoniacal nitrogen – sometimes referred to as TAN</td>
   </tr>
   <tr>
    <td>NI</td>
    <td>Nitrification Inhibitor</td>
   </tr>
   <tr>
    <td>NO</td>
    <td>Nitric oxide – a tropospheric air pollutant</td>
   </tr>
   <tr>
    <td>NO<sub>2</sub></td>
    <td>Nitrogen dioxide – a tropospheric air pollutant</td>
   </tr>
   <tr>
    <td>NO<sub>2</sub><sup>-</sup></td>
    <td>Nitrite</td>
   </tr>
   <tr>
    <td>NO<sub>3</sub><sup>-</sup></td>
    <td>Nitrate – present as a secondary pollutant in atmospheric PM and a eutrophying pollutant of aquatic systems</td>
   </tr>
   <tr>
    <td>NO<sub>x</sub></td>
    <td>Nitrogen oxides – a combination of NO and NO<sub>2</sub></td>
   </tr>
   <tr>
    <td>Norg</td>
    <td>Organic nitrogen</td>
   </tr>
   <tr>
    <td>NPK</td>
    <td>Nitrogen, Phosphorus and Potassium in combination</td>
   </tr>
   <tr>
    <td>N<sub>r</sub></td>
    <td>Reactive Nitrogen – a term used for a variety of nitrogen compounds that support growth directly or indirectly, as opposed to N<sub>2</sub> which is inert</td>
   </tr>
   <tr>
    <td>NUE</td>
    <td>Nitrogen Use Efficiency – typically defined as the ratio of N in outputs divided by the N in inputs. May be expressed for different systems such as crops, livestock, food chain and the whole economy</td>
   </tr>
   <tr>
    <td>O<sub>3</sub></td>
    <td>Ozone</td>
   </tr>
   <tr>
    <td>OECD</td>
    <td>Organization for Economic Cooperation and Development</td>
   </tr>
   <tr>
    <td>P</td>
    <td>Phosphorus</td>
   </tr>
   <tr>
    <td>PM</td>
    <td>Particulate Matter – includes NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>-</sup> as major components. PM<sub>10</sub> and PM<sub>2.5</sub> refer to atmospheric particulate matter (PM) that has a diameter of less than 10 and 2.5 micrometres respectively</td>
   </tr>
   <tr>
    <td>R-NH<sub>2</sub></td>
    <td>Organic nitrogen compounds</td>
   </tr>
   <tr>
    <td>S</td>
    <td>Sulphur</td>
   </tr>
   <tr>
    <td>SEA</td>
    <td>Strategic Environmental Assessment</td>
   </tr>
   <tr>
    <td>Si</td>
    <td>Silicon</td>
   </tr>
   <tr>
    <td>SO<sub>2</sub></td>
    <td>Sulphur dioxide</td>
   </tr>
   <tr>
    <td>TAN</td>
    <td>Total Ammoniacal Nitrogen</td>
   </tr>
   <tr>
    <td>TFIAM</td>
    <td>Task Force on Integrated Assessment Modelling of the UNECE Air Convention</td>
   </tr>
   <tr>
    <td>TFRN</td>
    <td>Task Force on Reactive Nitrogen of the UNECE Air Convention</td>
   </tr>
   <tr>
    <td>TN</td>
    <td>Total Nitrogen</td>
   </tr>
   <tr>
    <td>UAN</td>
    <td>Urea Ammonium Nitrate</td>
   </tr>
   <tr>
    <td>UNECE</td>
    <td>United Nations Economic Commission for Europe</td>
   </tr>
   <tr>
    <td>UNEP</td>
    <td>United Nations Environment Programme</td>
   </tr>
   <tr>
    <td>UNFCCC</td>
    <td>United Nations Framework Convention on Climate Change</td>
   </tr>
   <tr>
    <td>VOCs</td>
    <td>Volatile Organic Compounds</td>
   </tr>
   <tr>
    <td>WGSR</td>
    <td>Working Group on Strategies and Review of the UNECE Air Convention</td>
   </tr>
   <tr>
    <td>WHO</td>
    <td>World Health Organization</td>
   </tr>
   <tr>
    <td>Zn</td>
    <td>Zinc</td>
   </tr>
  </table>
# Chapter I: Overview for policymakers

## Nitrogen opportunities for agriculture, food and environment

Mark A. Sutton, Cláudia M. d. S. Cordovil, Tommy Dalgaard, Clare M. Howard, Barbara Amon, Shabtai Bittman, Tom Misselbrook and Oene Oenema

### Goals and context

* Integrated sustainable nitrogen management offers the opportunity to link the multiple benefits of better nitrogen (N) use from environmental, economic and health perspectives, helping to avoid policy trade-offs while maximizing synergies.

* By demonstrating the multiple benefits of taking action on nitrogen, a much stronger mobilization for change is expected, catalysing progress towards many of the United Nations Sustainable Development Goals.

* The present document has been prepared under the lead of the United Nations Economic Commission for Europe (UNECE) Convention on Long-range Transboundary Air Pollution (Air Convention) as part of its work to reduce air pollution impacts, including from acidification, eutrophication, ground-level ozone and particulate matter (PM), as these affect human health, biodiversity and economy.

* There are multiple co-benefits of taking action on nitrogen, especially for climate mitigation, stratospheric ozone and the protection of water resources, including groundwater, rivers, lakes, coastal zones and the wider marine environment.

* The present guidance is simultaneously a contribution from the International Nitrogen Management System (INMS), delivering support to the developing Inter-convention Nitrogen Coordination Mechanism (INCOM) in partnership with the United Nations Environment Programme (UNEP), the Global Environment Facility (GEF) and the International Nitrogen Initiative (INI).

### Main points

* Nitrogen is critical as a major nutrient to allow food, fibre and biofuel production. However, the efficiency with which nitrogen is used is very low when considering the full chain from fertilization to human consumption and waste.

* A distinction is made between unreactive atmospheric dinitrogen ($N_2$) and reactive nitrogen forms ($N_r$), which represent valuable resources. Around 80 per cent of anthropogenic $N_r$ production is wasted as air and water pollution and through denitrification back to $N_2$.

* The present guidance document is focused on agriculture in the context of the food system, and includes specific information on the principles and measures that can reduce emissions to the air of ammonia ($NH_3$), nitrogen oxides ($NO_x$), nitrous oxide ($N_2O$) and $N_2$, plus nitrate ($NO_3^-$) and other $N_r$ leaching to water and total N loss.

* Informed by 10 key points that underpin nitrogen cycling, the document reflects on 24 principles of integrated sustainable nitrogen management. The document then identifies 76 specific measures to improve nitrogen management, increase nitrogen use efficiency and reduce polluting losses to the environment.

* The document describes: 5 livestock diet measures; 18 housing measures; 12 manure storage/processing measures; 5 nutrient recovery measures; 20 field-based measures for application of organic and inorganic fertilizers; and 16 land-use and landscape measures.

* The accompanying discussion of basic principles will help strengthen the development of future strategies for pollution and sustainable development, and the establishment of coherent "packages of measures" that maximize the synergies.
A. Background

1. Ever since crops and livestock were first domesticated, the maintenance of civilization has been intrinsically linked to human alteration of the natural nitrogen cycle. The cultivation of crops and rearing of livestock mobilize nitrogen (N) and other nutrients, which are then transported as food, feed and fibre to villages, towns and cities (Lassaletta and others, 2014). Nitrogen-fixing crops and manures have been used for millennia to help increase harvests (for example, Columella, *On Agriculture* 2.13.1, trans. Boyd Ash, 1941), while the last 200 years have seen the mobilization of additional nitrogen, including from mined resources (for example, guano, saltpetre, coal distillation) and, ultimately, in the twentieth century, from the manufacture of inorganic fertilizers directly from atmospheric dinitrogen ($N_2$) (Sutton and others, 2011). As the scale of human alteration of the nitrogen cycle has increased, so have the consequences. Inorganic nitrogen fertilizers (including manufactured urea) have allowed the production of surplus food and feed in many regions, permitting substantial increases in human and animal populations (Erisman and others, 2008), with consumption of animal products by humans in excess of dietary needs across much of the UNECE region (Westhoek and others, 2014, 2015; Springmann and others, 2018).

2. This transformation of the global nitrogen cycle, especially over the last century, has led to a web of pollution problems linking the human production and use of nitrogen compounds with multiple environmental threats. Together with nitrogen compounds formed during combustion processes, and those mobilized through wastewater, nitrogen pollution currently affects all environmental media across the whole of planet Earth.

3. Until recently, efforts to address nitrogen pollution had largely been fragmented. This was mainly a consequence of fragmentation in environmental policymaking, management and science between environmental media and issues such as air pollution, water pollution, greenhouse gas (GHG) emissions, stratospheric ozone depletion, biodiversity loss and soil protection. Each of these issues is affected by nitrogen pollution, which thereby acts as a linking driver between many issues related to environment, economy, health and well-being. Traditional fragmentation of policies between these issues has slowed progress in the achievement of policy goals by reducing the coherence of local, national and international actions across the nitrogen cycle, risking trade-offs that can act as barriers to change (Oenema and others, 2011a, 2011b).

4. The emerging recognition of the way that nitrogen links all these issues is now leading to a major policy opportunity to mobilize change. A joined-up approach across the nitrogen cycle can help develop the gravity of common cause between air pollution, water pollution, climate change, stratospheric ozone depletion, biodiversity loss, health and economy (Oenema and others, 2011b; Sutton and others, 2013, 2019; Zhang and others, 2015; Leip and others, 2015; Kanter and others, 2020).

5. UNECE has long been a pioneer in developing such

joined-up approaches. These include the Protocol to Abate Acidification, Eutrophication and Ground-level Ozone (Gothenburg Protocol, signed in 1999 and amended in 2012) to the Convention on Long-range Transboundary Air Pollution (Air Convention), which was itself signed in 1979. The amended Protocol came into force on 7 October 2019. The Gothenburg Protocol includes ceilings to limit emissions of sulphur dioxide ($SO_2$), nitrogen oxides ($NO_x$) and ammonia ($NH_3$) up to 2020, together with national commitments to reduce emissions of $SO_2$, volatile organic compounds (VOCs), particulate matter (PM), NO and $NH_3$ as from 2020 and onwards, as these contribute to acidification, eutrophication, ground-level ozone and PM. This multi-pollutant, multi-effect approach has encouraged further efforts to understand the many air pollution impacts and interactions of nitrogen. Following the establishment of the Task Force on Reactive Nitrogen (TFRN) in 2007 (ECE/EB.AIR/91/Add.1, decision 2007/1), the *European Nitrogen Assessment: Sources, effects and policy perspectives* (Sutton and others, 2011) extended the approach to consider the full range of nitrogen interactions linking air, water, climate, ecosystems and soils, including identification of abatement options.

6. Concerning agricultural sources of air pollution, most effort under the Gothenburg Protocol has focused on $NH_3$, which, in the UNECE region, is mainly emitted from animal excreta and nitrogen-containing fertilizers. This led to the establishment of the Guidance document on preventing and abating ammonia emissions from agricultural sources (Ammonia Guidance Document) as a comprehensive reference manual, revised in 2012 (ECE/EB.AIR/120) (published as Bittman and others, 2014). This document is complemented by the UNECE Framework Code for Good Agricultural Practice for Reducing Ammonia Emissions (ECE/EB.AIR/129), a shorter document describing voluntary approaches, which can also form the starting point for Parties to establish, publish and disseminate their own national ammonia codes, as required under annex IX to the Gothenburg Protocol.

7. With the improved understanding emerging from the European Nitrogen Assessment (Sutton and others, 2011), it was agreed by the Air Convention that there was a need for guidance on mitigating all forms of nitrogen, with the priority in the first instance being to focus on agricultural sources relevant across the UNECE region. This was deemed necessary to support the objectives of the Gothenburg Protocol (twenty-second preambular para. on consideration of the full biogeochemical nitrogen cycle; art. 4 (1) on exchange of information and technology; art. 6 (1) (g) on the implementation of management programmes to reduce emissions; annex IX, para. 2, on reducing nitrogen losses from the whole nitrogen cycle; and the revised Gothenburg Protocol (tenth preambular para. on the influence of the nitrogen cycle and the potential synergies with and trade-offs between air pollution and climate change; art. 7 (3) (d) on the calculation of nitrogen budgets, nitrogen use efficiency and nitrogen surpluses and their improvements; and art. 10 (4) on the need to revise annex IX). As part of the 2016–2017 work plan for the implementation of the Convention agreed by the Executive Body at its thirty-fourth session
(Geneva, 18 December 2015), the Task Force on Reactive Nitrogen undertook to "Initiate the development of an ECE guidance document that describes an integrated approach, addressing multiple compounds and their synergies, with regard to nitrogen management in agriculture and illustrates its co-benefits" (ECE/EB.AIR/133/Add.1, item 2.3.4).

8. Progress in the development of this guidance document was facilitated by assistance from the European Commission Directorate-General for Environment and from the International Nitrogen Management System (INMS). INMS provides global and regional scientific support for international nitrogen policy development, practice and awareness-raising, with financial support through the United Nations Environment Programme (UNEP) and the Global Environment Facility (GEF), while building partnerships, including through the International Nitrogen Initiative and the Global Partnership on Nutrient Management.

9. The present guidance document simultaneously provides a contribution to the developing activity of the Inter-convention Nitrogen Coordination Mechanism (INCOM), currently being established through the Nitrogen Working Group under the auspices of the UNEP Committee of Permanent Representatives. This forms a central part of the Roadmap for Action on Sustainable Nitrogen Management 2020-2022 (UNEP 2019a, 2019b) in implementing United Nations Environment Assembly resolution 4/14 on sustainable nitrogen management (see UNEP/EA.4/Res.14).

10. The financial support from UNEP/GEF and the European Commission, together with the Global Challenges Research Fund South Asian Nitrogen Hub – a regional contribution to INMS – has allowed the work to be developed through two dedicated workshops (Brussels, 11–12 October 2016 and 30 September–1 October 2019), including contributions from Eastern Europe, the Caucasus and Central Asia.

11. The importance of the activities has been emphasized as part of the revised mandate of TFRN (ECE/EB.AIR/142/Add.2, decision 2018/6, annex, para. 3 (g) and (h)), including its functions to:

3 (g) Explore the relationships between emission mitigation of ammonia and other nitrogen compounds in the context of nitrogen benefits for food and energy production, considering the opportunities to share experiences on tools for improved nitrogen management and approaches to improve the uptake of the most promising options;

(h) Initiate work on the potential for mitigation strategies that simultaneously reduce ammonia and nitrogen oxide emissions from soils considering the increasing share of NOx from agriculture and the potential relationships with mitigation of nitrous oxides and dinitrogen.

12. The present Guidance document is a result of this process. It is anticipated that the document will help mobilize efforts to control air pollution from agricultural sources in the context of the wider nitrogen cycle. In particular, the Guidance document aims to foster change by clearly identifying the multiple co-benefits of reducing

nitrogen emissions, as relevant for air quality, climate change, water quality, human health, ecosystems and economy. By aiming to harvest the multiple co-benefits of better nitrogen management, a more coherent and effective response may be expected that maximizes synergies, minimizes trade-offs and accelerates progress towards achievement of the United Nations Sustainable Development Goals.

## B. Approach of the Guidance document

### 1. Scope and target groups

13. The present Guidance document on integrated sustainable nitrogen management focuses on the agricultural sector, including both cropping and livestock systems. While humans have implicitly engaged in managing nitrogen over many millennia, this has not always been sustainable or integrated. The use of the word "sustainable" in the title emphasizes the importance of considering the full set of environmental, social and economic consequences of nitrogen use in agriculture. It is consistent with the adoption, in March 2019, of United Nations Environment Assembly resolution 4/14 on sustainable nitrogen management and the follow-up Colombo Declaration on Sustainable Nitrogen Management (UNEP, 2019c), and reflects the fact that sustainable nitrogen management is a prerequisite for achieving most of the Sustainable Development Goals.

14. The word "integrated" also features in the title of the present guidance document. This reflects recognition by experts and stakeholders of the fact that an integrated approach is needed to link air, water, climate, stratospheric ozone and other issues as a basis for the development of sound strategies. In this way, "integrated" is here seen as an opportunity and requirement to be aware of synergies and trade-offs in order to mobilize more effective outcomes. The approach is also fully consistent with ongoing developments, coordinated through UNEP and INMS, towards the establishment of an Inter-convention Nitrogen Coordination Mechanism (INCOM) (Sutton and others, 2019). This activity aims to promote synergies through cooperation between the Air Convention and other intergovernmental conventions and programmes, thereby accelerating progress in nitrogen-related challenges in implementing United Nations Environment Assembly resolution 4/14.

15. The present document, prepared under the lead of the Air Convention, can also be seen as providing input to the wider coordination of INCOM, with benefits for many other multilateral environmental agreements. The present guidance document is aimed at policymakers, regulators and agricultural advisors, who will benefit from the overview of principles and measures presented when formulating integrated sustainable nitrogen management strategies and policies. It is anticipated that future materials may be prepared that more specifically target the needs of different farmer groups across the UNECE region and globally.
## 2. United Nations Economic Commission for Europe categories and magnitude of effect

### (a) United Nations Economic Commission for Europe categories

16. The present guidance document adopts the UNECE approach established for the Ammonia Guidance Document (ECE/EB.AIR/120, para. 18), where each abatement/mitigation measure is assigned one of the three following categories according to expert judgement<fnref n="1" />:

(a) Category 1 techniques and strategies: These are well-researched, considered to be practical or potentially practical and there are quantitative data on their abatement efficiency at least on the experimental scale;

(b) Category 2 techniques and strategies: These are promising, but research on them is at present inadequate, or it will always be difficult to generally quantify their abatement efficiency. This does not mean that they cannot be used as part of a nitrogen abatement strategy, depending on local circumstances;

(c) Category 3 techniques and strategies: These have not yet been shown to be effective or are likely to be excluded on practical grounds.

17. Under this UNECE approach, no connection is made to the profitability or otherwise of the measures in assigning these categories, which are purely based on technical criteria. It is therefore quite feasible for a measure to be listed as category 1, while not yet being considered economical from a sector viewpoint in the absence of appropriate support. This approach can be considered distinct from and complementary to definitions of best available techniques (BATs), which typically incorporate criteria about not entailing excessive costs. In this way, it becomes much easier for experts to assign the UNECE categories (with costs of measures specified separately where available), as compared with the technical-political negotiations that are needed to agree what constitutes relevant standards for BATs. In the Technical overview (chapter II) below, each of the measures is assigned a UNECE category for each nitrogen form according to the following colour code: green (category 1); amber (category 2); and red (category 3). It should be emphasized that the red colour code for category 3 does not indicate any adverse effect, but simply signals that the measure has not yet been demonstrated to be effective. This may mean that further research and development is needed. Some measures included in this document are assigned category 3 for all forms of nitrogen pollution. These are included either: (a) because they are frequently discussed and an objective assessment is needed regarding their ineffectiveness; or (b) because further development is needed to demonstrate their potential.

18. The UNECE approach is here extended to allow each measure to be assigned a category according to its suitability for each major nitrogen form: NH₃; NOₓ<fnref n="2" />; nitrous oxide (N₂O); nitrate (NO₃⁻), including other water-based losses of nitrogen compounds; dinitrogen (N₂); and overall nitrogen loss. The document also includes the term "reactive nitrogen" (N₃), which refers to all nitrogen compounds with the exception of N₂, which is unreactive (see figure I.1).

### (b) Magnitude of effect

19. The present guidance document does not replace the UNECE Ammonia Guidance Document (ECE/EB.AIR.120), which provides much more detailed information on quantitative abatement efficiency and the costs of measures for NH₃. By contrast, it is not feasible to provide quantitative details for all the nitrogen components listed for all measures. To address this situation, a qualitative indication is provided in this document for each measure concerning its effectiveness in reducing losses of each nitrogen form. The following system is used:

(a) Downward arrows indicate a reduction in losses: ↓, small to medium effect; ↓↓, medium to large effect;

(b) Upward arrows indicate an increase in losses: ↑, small to medium effect; ↑↑, medium to large effect;

(c) Little or no effect, indicated by ~;

(d) Uncertain, indicated by ?.

20. The magnitude of effect can be considered as an indication of "effectiveness" of the measure as distinct from the extent to which the measure is "applicable" in different contexts. Arrows indicate outcomes at the scale of the measure described (for example, animal housing, fertilizer application), but wider system consequences also need to be considered. Where a measure is considered to increase losses of a specific nitrogen form, it is, by definition, assigned to category 3 for that nitrogen form. Where clarification is necessary, magnitude of effect of a measure is described in comparison to a specified reference system.

21. Some measures targeted to benefit one form of nitrogen pollution can increase the risk of losses in other nitrogen forms. Such trade-offs (or "pollution swapping") are not inevitable and may often be avoided by appropriate actions that are not easy to summarize in tabular form. For this reason, the text describing each measure will typically mention main interactions, while chapter III is dedicated to the principles of good nitrogen management, helping to minimize trade-offs and maximize synergies. This highlights the opportunity to develop coherent "packages of measures". For example, while many of the measures are applicable to both conventional and organic systems (as well as to other agroecological farming systems), overall packages of measures would be expected to differ according to climate

<footnote n="1">¹ The UNECE categories and system for representing magnitude of effect described here in chapter I, paras. 16–20, of the present document apply throughout the present document.</footnote>

<footnote n="2">² Nitrogen oxides (NOₓ) represent a mix of nitric oxide (NO) and nitrogen dioxide (NO₂). Emissions of NOₓ from agricultural soils occur mainly in the form of NO, although emissions as NO₂ may also be possible. Reactions of NO with ozone (O₃) within the air space of plant canopies can mean that a substantial fraction of emission occurs as NO₂ at the canopy scale. Although the research community has mainly referred in the past to NO emissions from soils, for these reasons, and in the interests of consistency with the Convention on Long-range Transboundary Air Pollution (Air Convention) nomenclature, this document refers primarily to NOₓ emissions from soils.</footnote>
<figure><img src="image_6.png" /><figcaption>**Figure I.1:** Major forms of nitrogen occurring in the environment</figcaption></figure>

Source: The figure was created for the present document.

Note: The sum of all forms except N₂ is often termed fixed or reactive nitrogen (Nₜ).

and farming system.

22. Some forms of nitrogen loss tend to be much larger than others in terms of the overall mass of nitrogen involved. The largest losses often occur as NH₃ emission, nitrate and other nitrogen leaching/run-off, and as denitrification to N₂. By contrast, emissions of nitrous oxide (N₂O) and NOₓ tend to represent a small fraction of nitrogen flows (often ~1 per cent of inputs). Although N₂O and NOₓ losses from agricultural systems therefore only make a minor contribution to total nitrogen loss, they are relevant because of their specific impacts on air quality, climate and stratospheric ozone depletion. Conversely, although dinitrogen (N₂) emissions through denitrification are environmentally benign, they represent a potentially large fraction of available nitrogen resources. This means that abatement of N₂ emissions is important because it can help improve overall system efficiency, decreasing the need for fresh production of nitrogen compounds and therefore helping to reduce all nitrogen loss pathways and impacts. The philosophy of the present guidance document is to promote transformation towards a "circular economy" for nitrogen, as illustrated in figure I.2.

### C. Main messages of the Guidance document

23. The core of the present Guidance document consists of a set of principles for sustainable nitrogen management followed by detailed consideration measures to reduce N

losses from major parts of the agrifood system.

24. The description of sustainable nitrogen management is underpinned by ten key points of nitrogen cycling, as summarized in figure I.3. The fundamental reflections of biogeochemistry must be recognized if human management of the nitrogen cycle is to move from a system emphasizing new production of N compounds and wasteful losses to a more circular system, which maximizes the recovery and reuse of available N resources.

25. Twenty-four principles of integrated sustainable nitrogen management are identified and summarized in the Technical overview (chapter II). The first listed principle encapsulates the overall philosophy of the approach:

Principle 1: The purpose of integrated sustainable nitrogen management in agriculture is to decrease nitrogen losses to the environment to protect human health, climate and ecosystems, while ensuring sufficient food production and nitrogen use efficiency, including through appropriately balanced nitrogen inputs.

26. All of the principles are important, with the wide diversity of principles reflecting the diversity of N forms, issues, and impacts. By considering these principles, a sound foundation is provided to inform the selection of suitable measures.

27. At the heart of nitrogen management is the idea that taking a nitrogen cycle perspective allows synergies to be identified and trade-offs minimized. This can be illustrated by the comparison of principles 4, 5 and 6 of sustainable nitrogen management:

(a) Principle 4: Possible trade-offs in the effects of N loss
<figure><img src="image_7.png" /><figcaption>**Figure I.2:** Simplified comparison of linear and circular economies for nitrogen in the agrifood system</figcaption></figure>

Source: The figure was created for the present document.

<figure><img src="image_8.png" /><figcaption>**Figure I.3:** Ten key points of nitrogen cycling</figcaption></figure>

Source: The figure was created for the present document.

Note: These key points underpin the principles of integrated sustainable nitrogen management. The numbers reflect the ordering as described in chapter III of the present document. Humans introduce huge amounts of additional reactive nitrogen into the nitrogen cycle, meaning that the system is now out of balance.
abatement/mitigation measures may require priorities to be set, for example, which adverse effects should be addressed first;

(b) Principle 5: Nitrogen input control measures influence all N loss pathways;

(c) Principle 6: A measure to reduce one form of pollution leaves more N available in the farming system, so that more is available to meet crop and animal needs.

28. Principle 7 highlights that “The nitrogen input-output balance encapsulates the principle that what goes in must come out”. This can be translated to ensure that inputs match crop and livestock needs, allowing opportunities to reduce all N losses simultaneously (principle 8), as well to reflect spatial variations between vulnerability of agricultural and semi-natural land (principles 9 and 10). The focus on land-use and landscape management is reflected in the principle whereby unfertilized agricultural land and woodlands are recognized as being able to provide buffers that can strengthen landscape resilience to decrease adverse effects in the local environment (principle 11), so long as this does not contravene any specific habitat conservation objectives for the identified buffer ecosystems themselves.

29. It is recognized that nitrogen management must be seen in relation to other limiting factors, which need to be optimized to have the largest possible reduction in nitrogen pollution, both for crop and livestock systems (principles 12 and 13). This is extended by principles that recognize the need to consider nitrogen management in relation to wider management of all nutrients and biogeochemical cycles (including carbon (C), phosphorus (P), sulphur (S), silicon (Si), micronutrients, etc.) and water resources (principles 19, 20 and 21).

> "Manure once it is spread, should be ploughed in immediately and covered over, that it may not lose its strength from the heat of the sun".

Columella, circa 50 AD

30. Principles 14, 15, 16 and 17 reflect the physicochemical basis for reducing emissions, including slowing urea hydrolysis, avoiding exposure of ammonium-rich resources to air and the heat of the sun and slowing nitrification and denitrification, which simultaneously maximize the potential to usefully manage nitrogen resources.

31. It is recognized that nitrogen management in agriculture is intimately linked to the entire food system. This means that both dietary measures in livestock and human dietary choices, as well as waste management, will be essential if ambitious sustainability goals are to be achieved (principle 18). At the same time, ruminant dietary strategies need to consider the possible impact on methane emissions (principle 22), where certain measures will be contraindicated for sustainable nitrogen and methane

management.

32. Further principles recognize the social and economic dimension, including local aspects among the various actors in agriculture and the food chain, where these actors have a shared responsibility in N management (principle 2), including food supply, food processing, retail and consumers. As a part of these principles, it is acknowledged that “the whole farm-level is often a main integration level for emission-abatement/mitigation decisions” (principle 24), in addition to the wider actions of citizens and other actors in the food system. In the case of farmers, principle 23 recognizes that the cost and effectiveness of measures to reduce N losses need to take account of the regional opportunities and constraints of farmers, including effects of farm size, farm structure and economic context. Altogether, the principles show that integrated sustainable nitrogen management is an opportunity for different actors in the agrifood system to work together, where efficiency, waste reduction, environmental stewardship and investment for profitable food production all go hand-in-hand.

33. The Technical overview (chapter II) and chapters IV–VI provide a detailed listing of the measures identified, indicating the opportunity for abatement and mitigation of different nitrogen forms relevant for air pollution, water pollution, climate change, biodiversity, human health, stratospheric ozone, etc. Lastly, chapter VII reflects briefly on how the different measures may fit together, giving examples of possible “packages of measures” that can provide a coherent approach to sustainable nitrogen management according to the levels of ambition needed to meet different local, national and international goals.

34. The present document takes a significant step forward in supporting international policy development by applying understanding of the nitrogen cycle to catalyse sustainable development across multiple challenges. In this way, the document breaks new ground by providing guidance on reducing losses of all main nitrogen forms: NH₃, N₂O, NOₓ, NO₃⁻ and N₂. While the integration is new and draws on the latest research, it also depends on long-established experience. This point was made by a Roman farmer writing nearly 2,000 years ago:

> "Manure once it is spread, should be ploughed in immediately and covered over, that it may not lose its strength from the heat of the sun and that the soil, being mixed with it, may grow fat on the aforesaid nourishment. And so, when piles of manure are distributed in a field, the number of those so scattered should not exceed what the ploughmen can dig in on the same day."

Columella, On Agriculture 2.5.2 (trans. Boyd Ash, 1941)

35. This measure and its principles, as explained by Columella, are still relevant today and represented in the present guidance document. The example shows how measures to reduce nutrient losses have been recognized for centuries. The challenge is to put them into practice.
D. References

Bittman, S. and others, eds. (2014). *Options for Ammonia Mitigation: Guidance from the UNECE Task Force on Reactive Nitrogen* (Edinburgh: Centre for Ecology and Hydrology). Available at http://www.clrtap-tfrn.org/sites/clrtap-tfrn.org/files/documents/AGD_final_file.pdf.

Boyd Ash, H., transl. (1941). *Columella. On Agriculture, Volume I: Books 1-4*. Loeb Classical Library 361 (Cambridge, Massachusetts: Harvard University Press).

Erisman, J.W. and others (2008). How a century of ammonia synthesis changed the world. *Nature Geoscience*, vol. 1, No. 10 (October), pp. 636–639.

Kanter, D.R. and others (2020). Nitrogen pollution policy beyond the farm. *Nature Food*, vol. 1 (January), pp. 27–32.

Lassaletta, L. and others (2014). Food and feed trade as a driver in the global nitrogen cycle: 50-year trends. *Biogeochemistry*, vol. 118, No. 1–3 (April), pp. 225–241.

Leip, A. and others (2015). Impacts of European livestock production: nitrogen, sulphur, phosphorus and greenhouse gas emissions, land-use, water eutrophication and biodiversity. *Environmental Research Letters*, vol. 10, No. 11 (November), art. No. 115004.

Oenema, O. and others (2011a). Nitrogen in current European policies, chapter 4 in *The European Nitrogen Assessment: Sources, Effects and Policy Perspectives*, Sutton, M.A. and others, eds. (Cambridge: Cambridge University Press).

Oenema, O. and others (2011b). Developing integrated approaches to nitrogen management, chapter 23 in *The European Nitrogen Assessment: Sources, Effects and Policy Perspectives*, Sutton, M.A. and others, eds. (Cambridge: Cambridge University Press).

Springmann, M. and others (2018). Options for keeping the food system within environmental limits. *Nature*, vol. 562, No. 7728 (October), pp. 519–525.

Sutton, M.A. and others, eds. (2011). *The European Nitrogen Assessment: Sources, Effects and Policy Perspectives* (Cambridge: Cambridge University Press).

Sutton, M.A. and others (2013). *Our Nutrient World: The challenge to produce more food and energy with less pollution*. Global Overview of Nutrient Management (Edinburgh: Centre of Ecology and Hydrology).

Sutton, M.A. and others (2019). The Nitrogen Fix: From nitrogen cycle pollution to nitrogen circular economy, in *Frontiers 2018/19: Emerging Issues of Environmental Concern* (Nairobi: United Nations Environment Programme (UNEP)), pp. 52–65.

United Nations Economic Commission for Europe (UNECE) (1999). *Protocol to Abate Acidification, Eutrophication and Ground-level Ozone* (Gothenburg Protocol, revised 2012).

UNECE (2015). *Framework Code for Good Agricultural Practice for Reducing Ammonia Emissions*. Available at http://www.unece.org/environmental-policy/conventions/envlrtapwelcome/publications.html.

UNEP (2019a). *Roadmap for action on Sustainable Nitrogen Management 2020–2022*. Available at https://apps1.unep.org/resolution/?q=node/286.

UNEP (2019b). *Concept note to the Roadmap for action on Sustainable Nitrogen Management 2020–2022*. Available at https://apps1.unep.org/resolution/?q=node/286.

UNEP (2019c). *Colombo Declaration on Sustainable Nitrogen Management*. Launch of United Nations Global Campaign on Sustainable Nitrogen Management, 23 and 24 October 2019, Colombo. Available at https://apps1.unep.org/resolution/?q=node/286.

Westhoek, H. and others (2014). Food choices, health and environment: Effects of cutting Europe's meat and dairy intake. *Global Environmental Change*, vol. 26 (May), pp. 196–205.

Westhoek, H. and others (2015). *Nitrogen on the Table: The influence of food choices on nitrogen emissions and the European environment*. European Nitrogen Assessment Special Report on Nitrogen and Food (Edinburgh: Centre for Ecology and Hydrology).

Zhang, X. and others (2015). Managing nitrogen for sustainable development. *Nature*, vol. 528, No. 7580 (November), pp. 51–59.
<figure><img src="image_9.png" /></figure>

# Chapter II: Technical overview

## Integrating principles and measures for sustainable nitrogen management in the agrifood system

Mark A. Sutton, Barbara Amon, Shabtai Bittman, Klaus Butterbach-Bahl, Tommy Dalgaard, Lars Stoumann Jensen, Tom Misselbrook and Oene Oenema

36. The guidance provided in this document is structured around four main themes:

(a) **Principles of integrated sustainable nitrogen management.** Chapter III provides the background to help understand the integrated approach, including key points of nitrogen (N) cycling, dimensions of integration and principles of the measures;

(b) **Housed livestock, manure storage and manure processing.** Chapter IV explains the rationale for an integrated approach to manure management from excretion to storage, including opportunities for processing that treat manure as a valuable nitrogen and nutrient resource to be recycled. The core of the chapter is a summary of the main dietary, housing, manure and nutrient recovery measures;

(c) **Field application of organic and inorganic fertilizers.** Chapter V considers the field use of manure, setting this in relation to opportunities for improved management of manufactured inorganic fertilizers. Following established norms, the term "inorganic fertilizers" includes manufactured urea fertilizer. The core of the chapter is a summary of the main measures associated with field application;

(d) **Land-use and landscape management.** Chapter VI explains how opportunities for integrated nitrogen management are provided by decisions at the land-use and landscape scale. While the main focus is on mitigation of adverse effects, measures may also contribute to abatement of nitrogen emissions. The core of the chapter is a summary of the most important measures available at the landscape scale.

37. This Technical overview includes an indication of the performance of each measure for each nitrogen form (see figure II.1), according to the UNECE categories<fnref n="3" />.

38. Further details on the performance of each measure, including a qualitative indication of the magnitude of effects, are provided in chapters IV, V and VI. A reduction in "Overall N loss" indicates potential for indirect reduction of all other N losses.

### A. Principles of integrated sustainable nitrogen management

39. Nitrogen (N) provides substantial benefits to society by boosting crop productivity, allowing richer diets for humans, including with increased meat and dairy production and consumption. However, N losses present multifaceted problems affecting air, water, human health, climate, biodiversity and economy. To grasp the principles of sustainable nitrogen management, it is first necessary to consider the key points of nitrogen cycling (see box II.1).

40. Integrated sustainable nitrogen management in agriculture has a dual purpose: to decrease N emissions/ losses, including to protect human health; the environment and climate; and to optimize the beneficial effects of N related to food production through balanced fertilization and circular economy principles.

41. Many environmental policies have a narrow scope concerning nitrogen management and would benefit from an integrated approach. For example, most NOx and NH3

<figure><img src="image_10.png" /><figcaption>**Figure II.1:** Illustration of the performance of each of the measures for each N form, according to UNECE categories assigned in this document</figcaption></figure>

*Source:* The figure was created for the present document.

<footnote n="3">³ See chapter I, paras. 16–20, of the present document for a description of the UNECE categories and system for representing the magnitude of effect.</footnote>
<figure><img src="image_11.png" /></figure>

Box II.1: Ten Key Points of nitrogen cycling relevant for integrated sustainable nitrogen management

1) **Nitrogen is essential for life.** It is an element of chlorophyll in plants and of amino acids (protein), nucleic acids and adenosine triphosphate in living organisms (including bacteria, plants, animals and humans). Nitrogen is often a limiting factor for plant growth.

2) **Excess nitrogen has a range of negative effects, especially on human health, ecosystem services, biodiversity, through air, water and climate change.** The total amounts of N introduced into the global biosphere by human activities have significantly increased during the last century (more than doubled) and have now exceeded critical limits for the so-called safe operating space for humanity.

3) **Nitrogen exists in multiple forms.** Most N forms are "reactive" (N₄) because they are easily transformed from one form to another through biochemical processes mediated by microorganisms, plants and animals and chemical processes affected by climate. Dinitrogen (N₂) is unreactive, forming the main constituent of air (78 per cent). Nitrogen is "double mobile" because it is easily transported by both air and water in the environment.

4) **The same atom of N can cause multiple effects** in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems and on human health. This phenomenon is termed the "nitrogen cascade", which has been defined as the sequential transfer of N₄ through environmental systems.

5) **Nitrogen moves from soil to plants and animals, to air and water bodies, and back again, with international transboundary pollution transport of most nitrogen forms.** These flows are a result of natural drivers and human activities, which have to be understood for effective N management.

6) **Human activities have greatly altered the natural N cycle and have made the N cycle more leaky.** Main factors include: creation of synthetic inorganic N fertilizer; land-use change; urbanization; combustion processes; and transport of food and feed across the world. These have resulted in nitrogen depletion in crop food/feed exporting areas and regional nitrogen enrichment in urban areas and those areas with intensive livestock farming. Regional segregation of food and feed production and consumption is also one of the main factors why N use efficiency at whole food system level has decreased in the world during the last decades.

7) **The nature and human alterations of the N cycle challenge the realization of both a circular economy and integrated sustainable nitrogen management.** Sustainable nitrogen management provides the foundation to strengthen an emerging "nitrogen circular economy", reducing N losses and promoting recovery and reuse.

8) **Nitrogen forms need to be near plant roots to be effective for plant growth.** Nitrogen uptake depends on the N demand by the crop, the root length and density, and the availability of NO₃⁻ and NH₄⁺ in the soil solution.

9) **Some crop types are able to convert non-reactive N₂ into reactive N forms (NH₃, amine, protein) by using specialist bacteria in plant root nodules.** This process of biological nitrogen fixation is an important source of reactive N in the biosphere including agriculture, which can also result in N pollution.

10) **Humans and animals require small amounts of protein N and amino acids for growth, development and functioning, but only a minor fraction of the N intake is retained in the body weight and/or milk and egg.** The remainder is excreted, mainly via urine and faeces, and this N can be recycled and reused.

sources have been included in the Gothenburg Protocol, but NOₓ emissions from agricultural soils, (semi-)natural NOₓ and NH₃ sources are excluded when assessing compliance with the Gothenburg Protocol emission reduction commitments, as are N₂O and N₂ emissions to air and N leaching to waters. Conversely, in the European Union Nitrates Directive<fnref n="4" />, all N sources in agriculture must be considered for reducing NO₃⁻ leaching, but NH₃, NOₓ, N₂O and N₂ emissions to air are not explicitly addressed.

1. Different dimensions of integration in nitrogen management

42. **Dimension 1: Cause and effect** are the basis for current N policies, as the effects on human health and the environment, caused by N emissions, drive policy measures to decrease these emissions.

43. **Dimension 2: Spatial and temporal integration** of all N forms and sources affecting a certain area and time scale in management plans are critical to ensure that multiple co-

<footnote n="4">⁴ Council Directive of 12 December 1991 concerning the protection of waters against pollution caused by nitrates from agricultural sources (91/676/EEC), Official Journal of the European Communities, L 375 (1991), pp. 1–8.</footnote>
<figure><img src="image_12.png" /></figure>

benefits of action are achieved, maximizing synergies while minimizing nitrogen trade-offs.

44. **Dimension 3: Multiple nutrients and pollutants** are brought together by nitrogen. As an element, N is unique in the diversity of its environment and sustainability relevance. Sustainable nitrogen management therefore encourages integration with other elements and compounds:

(a) Between $NH_3$ and $NO_x$, $SO_2$, VOCs and PM in air pollution;

(b) Between N and carbon, including $CO_2$ and $CH_4$ when considering climate effects;

(c) Between N, phosphorus (P), potassium (K) and silicon (Si) when considering freshwater and coastal eutrophication;

(d) Between N and all other essential plant nutrients (either macronutrients or micronutrients) when considering crop, livestock and human nutrition;

(e) Between N and irrigation water, when considering sustainable water management.

45. **Dimension 4: Integrating stakeholders' views** is an additional dimension and has to be done as early as possible during the design phase of nitrogen management plans and measures. Multiple stakeholder types ensure that policy measures are:

(a) Policy relevant by addressing the main issues;

(b) Scientifically and analytically sound;

(c) Cost-effective, with costs proportional to the objective to be achieved; and

(d) Fair to all actors/users.

46. **Dimension 5: Regional integration** aims at enhanced cooperation between regions and countries, incorporating the landscape scale. Arguments for regional integration are:

(a) Enhancement of markets;

(b) Creation of a "level playing field" for policy measures

(c) The transboundary nature of environmental pollution;

(d) Consideration of indirect pollution affects; and

(e) The increased effectiveness and efficiency of regional policies and related management measures.

47. The Gothenburg Protocol has demonstrated the benefits of developing an approach that integrates multiple pollutants and multiple effects. In the case of nitrogen, most $NO_x$ and $NH_3$ sources are included when defining the emissions ceilings, while further efforts are needed to integrate $NO_x$ emissions from agricultural soils, (semi-) natural $NO_x$ and $NH_3$ sources, and the relationships to $N_2O$ and $N_2$ emissions and $NO_3^-$ leaching. The need to bring these issues together was recently recognized in United Nations Environment Assembly resolution 4/14 on sustainable nitrogen management and its follow-up in the Colombo Declaration. These texts emphasize the win-win opportunities for environment, health and economy, including air quality, water quality, climate, stratospheric ozone and biodiversity protection, together with the provision of sustainable food and energy.

## 2. Principles of integrated sustainable nitrogen management

48. Twenty-four principles of integrated sustainable nitrogen management are identified below:

(a) **Principle 1: The purpose of integrated sustainable nitrogen management in agriculture is to decrease nitrogen losses to the environment to protect human health, climate and ecosystems, while ensuring sufficient food production and nitrogen use efficiency, including through appropriately balanced nitrogen inputs;**

(b) **Principle 2: There are various actors in agriculture and the food chain, and all have a role in N management.** There is a joint responsibility for all actors in the food chain, including for policymakers at several levels, to support a decrease of N losses and to share the cost and benefits of N abatement/mitigation measures;

(c) **Principle 3: Specific measures are required to decrease pathway-specific N losses.** This is because the loss mechanisms differ between $NH_3$ volatilization, $NO_3^-$ leaching, erosion of all Nr forms to surface waters, and gaseous emissions of $NO_x$, $N_2O$ and $N_2$ related to nitrification-denitrification processes. Pathway-specific measures relate to pathway-specific controlling factors;

> "Reduced N inputs or increased harvested outputs are thus an essential part of integrated nitrogen management while providing opportunities for increased economic performance."

*From principle 6*

(d) **Principle 4: Possible trade-offs in the effects of N loss abatement/mitigation measures may require priorities to be set, for example, which adverse effects should be addressed first.** Policy guidance is necessary to inform such priorities and properly weigh the options according to local to global context and impacts;

(e) **Principle 5: Nitrogen input control measures influence all N loss pathways.** These are attractive measures because reductions in N input (for example, by avoidance of excess fertilizer, of excess protein in animal diets, and of human foods with a high nitrogen footprint), lead to less nitrogen flow throughout the soil-feed-food system;

(f) **Principle 6: A measure to reduce one form of pollution leaves more N available in the farming system, so that more is available to meet crop and animal needs.** In order to realize the benefit of a measure to reduce N loss (and to avoid pollution swapping), the nitrogen saved by the measure needs to be matched by either reduced N inputs, increased
<figure><img src="image_13.png" /></figure>

**storage, or increased N in harvested outputs.** Reduced N inputs or increased harvested outputs are thus an essential part of integrated nitrogen management while providing opportunities for increased economic performance;

(g) **Principle 7: The nitrogen input-output balance encapsulates the principle that what goes in must come out,** and that N input control and maximization of N storage pools (in manure, soil and plants) are main mechanisms to reduce N losses (see figure II.2).

(h) **Principle 8: Matching nitrogen inputs to crop needs (also termed "balanced fertilization") and to livestock needs** offers opportunities to reduce all forms of N loss simultaneously, which can help to improve economic performance at the same time. Natural differences between crop and animal systems similarly imply opportunities from integrating animal and crop production and optimizing the balance of food types;

(i) **Principle 9: Spatial variations in the vulnerability of agricultural land to N losses** require spatially explicit N management measures in a field and/or landscape. This principle is applicable to field application of both organic and inorganic fertilizer resources;

(j) **Principle 10: Spatial variations in the sensitivity of natural habitats to N loadings** originating from agriculture highlight the need for site- and region-specific N management measures. A source-pathway-receptor approach at landscape scale may help to target specific hot spots, specific N loss pathways, and specific

sensitive or resilient areas;

(k) **Principle 11: The structure of landscape elements affects the capacity to store and buffer nitrogen flows.** This means that ecosystems with high N storage capacity (for example, woodlands and unfertilized agricultural land) tend to buffer the effects of N compounds emitted to the atmosphere, so that less N is transferred to other locations. In this way, woodlands, extensive agricultural land and other landscape features help absorb and utilize N inputs from atmospheric N deposition or N that would otherwise be lost through lateral water flow. This principle is the basis of planning to increase overall landscape resilience, where, for example, planting of new woodland (with the designated function of capturing N) may be used as part of a package of measures to help protect other habitats (including other woodland and ecosystems, where nature conservation objectives are an agreed priority);

(l) **Principle 12: In order to minimize pollution associated with N losses,** all factors that define, limit and reduce crop growth have to be addressed simultaneously and in balance to optimize crop yield and N use efficiency. Elements include: selecting crop varieties adapted to local climatic and environmental conditions; preparing an appropriate seedbed; ensuring adequate levels of all essential nutrient elements and water; and ensuring proper weed control, pest and disease management and pollution control.

(m) **Principle 13: In order to minimize pollution**

<figure><img src="image_14.png" /><figcaption>Figure II.2: Concept of the nitrogen input – output mass balance of mixed crop – livestock production systems</figcaption></figure>

Source: Modified from Oenema and others (2009).

Note: Total inputs must balance total outputs, following corrections for possible changes in storage within the system. The concept is applicable at field, farm, regional and global scales for all farm types (chapter III).
<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

Image 1: According to principle 12, all factors that limit crop growth have to be addressed simultaneously to reduce nitrogen pollution. The photograph shows trials of wheat for use as a winter cover crop. The middle variety was found to be sensitive to rust fungus infection, limiting its ability to take up nitrogen and reduce nitrogen pollution (photograph: © Shabtai Bittman).

associated with N losses, all factors that define, limit or reduce animal growth and welfare have to be addressed simultaneously and in balance to optimize animal production and N use efficiency, also to decrease N excretion per unit of animal produce. Elements include: selecting breeds adapted to the local climatic and environmental conditions; ensuring availability of high-quality feed and water; and ensuring proper disease, health, fertility and pollution control, including animal welfare;

(n) **Principle 14: Slowing down hydrolysis of urea and uric acid containing resources reduces NH₃ emissions.** Hydrolysis of these resources produces NH₃ in solution and locally increases soil pH, so slowing hydrolysis helps avoid the highest ammonium concentrations and pH, which can also reduce other N losses by avoiding short-term N surplus;

(o) **Principle 15: Reducing the exposure of ammonium-rich resources to the air is fundamental to reducing NH₃ emissions.** Hence, reducing the surface area, lowering the pH, temperature and wind speed above the emitting surface, and promoting rapid infiltration by dilution of slurries all reduce NH₃ emissions;

(p) **Principle 16: Slowing down nitrification (the biological oxidation of NH₄⁺ to NO₃⁻) may contribute to decreasing N losses and to increasing N use efficiency.** This is because NH₄⁺ can be held in soil more effectively than NO₃⁻, making it less vulnerable to losses via leaching and nitrification-denitrification processes than NO₃⁻.

(q) **Principle 17: Some measures aimed at reducing N₂O emissions may also reduce losses of N₂ (and vice versa) since both are related to denitrification processes.** Measures aimed at jointly reducing N₂O and N₂ losses from nitrification-denitrification may therefore contribute to saving N resources within the system and reducing climate effects at the same time;

(r) **Principle 18: Achieving major N₂O reductions from agriculture necessitates a focus on improving N use efficiency across the entire agrifood system using all available measures.** The requirement for wider system change is because of the modest potential of specific technical measures to reduce N₂O emissions from agricultural sources compared with the scale of ambitious reduction targets for climate and stratospheric ozone. It implies a requirement to consider system-wide changes in all aspects of the agrifood system, including human and livestock diets and management of fertilizer, biological and recycled N resources;

(s) **Principle 19: Strategies aimed at decreasing N, P and other nutrient losses from agriculture are expected to offer added mitigation benefits compared with single nutrient emission-abatement strategies, because of coupling between nutrient cycles.** A nitrogen focus provides a pragmatic approach that encourages links between multiple threats and element cycles, thereby accelerating progress;

(t) **Principle 20: Strategies aimed at optimizing N and water use jointly are more effective than single N fertilization and irrigation strategies, especially in semi-arid and arid conditions.** This underlines the need for an integrated approach in which the availability of both N and water are considered jointly, especially in those regions of the world where food production is limited by the availability of both water and N. The joint coupling of N and water management also underlies the safe storage of solid manures to avoid run-off and leaching;

(u) **Principle 21: Strategies aimed at enhancing N use efficiency in crop production and at decreasing N losses from agricultural land have to consider possible changes in soil organic carbon (C) and soil quality over time and the impacts of soil carbon-sequestration strategies.** Carbon sequestration is associated with N sequestration in soil due to reasonably conservative ratios of C:N in soils. Protection of soil organic matter against degradation ("nitrogen mining") is vital to sustain agricultural productivity in regions with low N input;

(v) **Principle 22: Strategies aimed at reducing N emissions from animal manures through low-protein animal feeding have to consider the possible impacts of diet manipulations on enteric methane (CH₄) emissions from ruminants.** Low-protein diets in ruminants are conducive to low N excretion and NH₃ volatilization, but tend to increase fibre content and CH₄ emissions, pointing to the need for dietary optimization for N and C;

(w) **Principle 23: The cost and effectiveness of measures to reduce losses of N need to take account of the practical constraints and opportunities available to farmers in the region where implementation is intended.** The effectiveness and costs must be examined as much as possible under practical farm conditions and, in particular, taking account of farm size and basic environmental limitations. Cost-effectiveness analysis
<figure><img src="image_17.png" /></figure>

should consider implementation barriers, as well as the side effects of practices on other forms of N and greenhouse gases in order to promote co-benefits;

(x) **Principle 24: The whole farm-level is often a main integration level for emission-abatement/mitigation decisions, and the overall effects of emission-abatement/mitigation measures will have to be assessed at this level,** including consideration of wider landscape, regional and transboundary interactions.

### 3. Tools for integrated nitrogen management approaches

49. The toolbox for developing integrated approaches to N management contains both tools that are uniformly applicable and more specific tools, suitable for just one dimension of integration. Important common tools are:

(a) Systems analysis, used especially by the science-policy-practice interface;

(b) Nitrogen input-output budgeting tools to integrate N sources and N species for well-defined areas at various scales (from farms to continents) and that are easy for farmers and policymakers to understand (as well as being compatible with data privacy regulations);

(c) Integrated assessment modelling and cost-benefit analyses. The "Driver-Pressure-State-Impact-Response" (DPSIR) framework can be used as a starting point for analysing cause-effect relationships conceptually and cost-benefit analysis (CBA) goes a step further by expressing costs and benefits of policy measures in monetary terms;

(d) Food-chain assessment and management relates to the planning and management of activities and information between actors in the whole food production-consumption chain, including suppliers, processors, retail, waste-recycling companies and citizens;

(e) Stakeholder dialogue and communication are essential for exchanging views of actors on N management issues. These can help make the concepts transparent and facilitate adoption of targets, as well as helping in the implementation of measures in practice;

(f) Abatement/mitigation measures, including best management practices, which have been shown to reduce emissions and impacts, as described in chapters IV-VI of the present document.

### B. Housed livestock, manure storage and manure processing

50. Measures to reduce N loss from housed livestock, manure storage and processing influence manure composition and the storage environment, with the result that conditions are unfavourable for emissions. The first crucial step is to adapt the N content in the livestock diet as closely as possible to the requirements of animals, for which five measures are identified.

51. $NH_3$ emissions will be small at low temperatures and low pH values if the contact of manure with ambient air is limited. Emissions of $N_2O$, $NO_x$ and $N_2$ will be reduced by low organic C content, sufficient oxygen availability and low nitrate concentrations. Concepts for best practices to reduce adverse environmental impacts require integrated approaches, detailed understanding of emissions at the process level, and the development of flexible solutions that match regional needs.

52. The following priorities are identified to reduce nitrogen losses from livestock housing:

(a) Reduction of indoor temperature, including by optimized ventilation;

(b) Reduction of emitting surfaces and soiled areas;

(c) Reduction of air-flow over soiled surfaces;

(d) Use of additives (for example, urease inhibitors, acidification); and

(e) Regular removal of manure to an outside store. Overall, 18 Housing Measures are identified (see table II.1).

53. The following priorities are identified to reduce N losses and to mobilize N recovery/reuse from manure storage, treatment and processing:

(a) Storing outside the barn in a dry location;

(b) Covering slurry stores;

(c) Manure treatment/processing to reduce slurry dry matter content, increase slurry $NH_4^+$ content and lower pH;

(d) Anaerobic digestion, solid/liquid separation and slurry acidification;

(e) Ensuring that all available nutrient resources are used effectively for crop growth;

(f) Improving nutrient recapture and recovery; and

(g) Production of value-added nutrient products from recycled manure N resources. In total, 12 Manure Measures related to storage/processing and 5 Nutrient Recovery Measures are identified (see table II.1).

54. Overall, measures related to livestock diets, housing, manure storage and manure reprocessing should be seen in relation to the flow of nitrogen and other nutrients, with significant synergy between the different stages. For example, N saved through optimized diets and low-emission stables provides an opportunity to increase N resources for manure recycling or direct application to fields (chapter V). It is important to remember the principles by which each measure works (chapter III) to maximize the synergies and avoid trade-offs. For example, in order to achieve the full benefit of reducing $NH_3$ emissions during animal housing, corresponding measures are needed during manure storage and manure spreading to avoid $NH_3$ emissions later in the system. The manure management chain provides a key example of an opportunity for circular economy thinking where reduced losses to the environment translate into increased resource availability (see figure I.2).
<figure><img src="image_18.png" /><figcaption>**Table II.1 : Measures related to livestock diets, livestock housing, manure storage and processing, and nutrient recovery. For explanation of colours, see figure II.1.**</figcaption></figure>

<table><thead><tr><th colspan="2">Measures related to livestock diets</th></tr></thead><tbody><tr><td><strong>Dietary Measure 1: Adapt protein intake in diet (dairy and beef cattle)</strong></td><td>Adaptation of crude protein in the diet to match the needs of animals is the first and most efficient measure to mitigate N emissions. This measure decreases the excretion of excess N and thus reduces emissions along the whole manure management chain. Increasing the energy/protein ratio in the diet is a well-proven strategy to reduce levels of crude protein. For grassland-based ruminant production systems, the feasibility of this strategy may be limited, as older grass may reduce feeding quality.</td></tr><tr><td><strong>Dietary Measure 2: Increase productivity (dairy and beef cattle)</strong></td><td>Increasing the productivity of dairy and beef cattle through an increase in milk yield or daily weight gain reduces CH<sub>4</sub> (and potentially N<sub>2</sub>O) emissions per kg of product.<sup>5</sup> A balance must be found between emission reduction through productivity increase and the limited capacity of cattle to deal with concentrates. The ability of cattle to convert protein from roughage, which is inedible for humans, to high-value protein is valuable from a resource and biodiversity perspective.</td></tr><tr><td><strong>Dietary Measure 3: Increase longevity (dairy cattle)</strong></td><td>Productivity can be increased through increasing milk production per year and through increasing the amount of milk production cycles. Optimized diet and housing conditions enable a higher longevity of dairy cattle, and therefore fewer replacement animals are needed, thereby reducing N losses per product.</td></tr><tr><td><strong>Dietary Measure 4: Adapt protein intake in diet (pigs)</strong></td><td>Feeding measures in pig production include phase feeding, formulating diets based on digestible/available nutrients, using low-protein amino acid-supplemented diets, and feed additives/supplements. The crude protein content of the pig ration can be reduced if the amino acid supply is optimized through the addition of synthetic amino acids.</td></tr><tr><td><strong>Dietary Measure 5: Adapt protein intake in diet (poultry)</strong></td><td>For poultry, the potential for reducing N excretion through feeding measures is more limited than for pigs because the conversion efficiency currently achieved on average is already high and the variability within a flock of birds is greater.</td></tr></tbody></table>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>

<figure><img src="image_23.png" /></figure>

<footnote n="5">5 This effect is noted without prejudice to any current or future agricultural policy (for example, the European Union Common Agricultural Policy) and other state aid measures oriented to conserving local traditional animal races, which emphasizes the need to consider the balance between issues.</footnote>
<figure><img src="image_24.png" /></figure>

Measures related to livestock housing

Housing Measure 1: Immediate segregation of urine and faeces (cattle)

A physical separation of faeces (which contain urease) and urine in the housing system reduces hydrolysis of urea, resulting in reduced NH₃ emissions from both housing and manure spreading. Solid-liquid separation will also reduce emissions during land-application, where urine infiltrates soil more easily than mixed slurry.

<figure><img src="image_25.png" /></figure>

Housing Measure 2: Regular cleaning of floors in cattle houses by toothed scrapers (cattle)

The emitting surface may be reduced by using "toothed" scrapers running over a grooved floor, thereby reducing NH₃ emissions. This also results in a cleaner floor surface with good traction for cattle to prevent slipping.

<figure><img src="image_26.png" /></figure>

Housing Measure 3: Regular cleaning of floors in cattle houses

Thorough cleaning of walking areas in dairy cattle houses by mechanical scrapers or robots has the potential to substantially reduce NH₃ emissions.

<figure><img src="image_27.png" /></figure>

Housing Measure 4: Frequent slurry removal (cattle)

Regular removal of slurry from under the slats in an animal house to a (covered) outside store can substantially reduce NH₃ emissions by reducing the emitting surface and the slurry storage temperature. It also reduces CH₄ emissions as manure is stored outside, under cooler conditions.

<figure><img src="image_28.png" /></figure>

Housing Measure 5: Increase bedding material (cattle with solid manure)

Use of bedding material that absorbs urine in cattle housing can reduce NH₃ emissions by immobilizing nitrogen and may also reduce N₂O emissions.

<figure><img src="image_29.png" /></figure>

Housing Measure 6: Barn climatization to reduce indoor temperature and air flow (cattle)

In houses with traditional slatted floors, barn climatization with slurry cooling, roof insulation and/or automatically controlled natural ventilation can reduce NH₃ emissions due to reduced temperature and air velocities and can also help reduce CH₄ emissions.

<figure><img src="image_30.png" /></figure>
<table><tr><td>Housing Measure 7: Use of acid air-scrubbers (cattle)</td><td>In the few situations where cattle are housed with forced ventilation, this measure can be considered as category 1 to reduce NH<sub>3</sub> emissions. However, most cattle are housed in naturally ventilated buildings across the ECE region. Recent developments explore the use of air-scrubbers with naturally ventilated buildings (for example, by directly extracting and scrubbing air from the slurry pit).</td><td></td></tr><tr><td>Housing Measure 8: Slurry acidification (pig and cattle housing)</td><td>Emissions of NH<sub>3</sub> can be reduced by acidifying slurry to shift the balance from NH<sub>3</sub> to NH<sub>4</sub><sup>+</sup>. Acidification in the livestock house will reduce NH<sub>3</sub> emissions throughout the manure management chain. Slurry acidified with sulphuric acid is not suitable as the sole feedstock for biogas production, only as a smaller proportion.</td><td></td></tr><tr><td>Housing Measure 9: Reduce emitting surface (pigs)</td><td>Ammonia emission can be reduced by limiting the emitting surface area through frequent and complete vacuum-assisted drainage of slurry from the floor of the pit. Other floor designs can be used, including partially slatted floors, use of inclined smoothly finished surfaces and use of V-shaped gutters.</td><td></td></tr><tr><td>Housing Measure 10: Regular cleaning of floors (pigs)</td><td>Thorough and regular cleaning of floors in pig houses by mechanical scrapers or robots has the potential to reduce NH<sub>3</sub> emissions substantially.</td><td></td></tr><tr><td>Housing Measure 11: Frequent slurry removal (pigs)</td><td>Regular removal of slurry from under the slats in the pig house to an outside store can reduce NH<sub>3</sub> emissions by reducing the emitting surface and the slurry storage temperature. It also reduces CH<sub>4</sub> emissions as manure is stored outside, under cooler conditions.</td><td></td></tr><tr><td>Housing Measure 12: Increase bedding material (pigs with solid manure)</td><td>Use of bedding material that absorbs urine in pig housing can reduce NH<sub>3</sub> emissions by immobilizing nitrogen and may also reduce N<sub>2</sub>O emissions. The approach can have a positive interaction with animal welfare measures. Regular changes of bedding may be needed to avoid N<sub>2</sub>O and N<sub>2</sub> emissions associated with deep-litter systems.</td><td></td></tr></table>

<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>
<figure><img src="image_37.png" /></figure>

<table><tr><td>Housing Measure 13: Barn climatization to reduce indoor temperature and air flow (pigs)</td><td>Surface cooling of manure with fans using a closed heat exchange system can substantially reduce NH<sub>3</sub> emissions. In slurry systems, this technique can often be retrofitted into existing buildings.</td><td></td></tr><tr><td>Housing Measure 14: Use of acid air-scrubbers (pigs)</td><td>Treatment of exhaust air by acid scrubbers has proven to be practical and effective at least for large-scale operations. This is most economical when installed in new houses. The approach also helps reduce odour and PM emission and may also contribute to reducing N<sub>2</sub>O and NO<sub>x</sub> emissions if the N recovered is used to replace fresh fertilizer N inputs.</td><td></td></tr><tr><td>Housing Measure 15: Use of biological air-scrubbers (pigs)</td><td>Biological air-scrubbers operate with bacteria that remove NH<sub>3</sub> and odours from the exhaust air. Careful management is needed to ensure that NH<sub>3</sub> captured in biological air-scrubbers (for example, organic biofilters) is not nitrified/denitrified, leading to increased emissions of N<sub>2</sub>O, NO<sub>x</sub> and N<sub>2</sub>. Recovery of the collected N<sub>r</sub> in bioscrubbers may help offset any increase, with opportunities to recover N<sub>r</sub> through use of biotrickling systems.</td><td></td></tr><tr><td>Housing Measure 16: Rapid drying of poultry litter</td><td>NH<sub>3</sub> emissions from battery deep-pit or channel systems can be lowered by ventilating the manure pit or by use of manure removal belts to dry manure. Keeping excreted N in the form of uric acid can also be expected to reduce N<sub>2</sub>O, NO<sub>x</sub> and N<sub>2</sub>, since this will also reduce nitrification and denitrification.</td><td></td></tr><tr><td>Housing Measure 17: Use of acid air-scrubbers (poultry)</td><td>Treatment of exhaust air by acid scrubber has been successfully employed to reduce NH<sub>3</sub> emissions in several countries. The main difference from pig systems is that poultry houses typically emit a much larger amount of dust. To deal with dust loads, multistage air-scrubbers with pre-filtering of coarse particles have been developed.</td><td></td></tr><tr><td>Housing Measure 18: Use of biological air-scrubbers (poultry)</td><td>Treatment of exhaust air by use of biotrickling filters (biological air-scrubbers) has been successfully employed in several countries to reduce NH<sub>3</sub> emissions, fine dust and odour. Multistage scrubbers have been developed to deal with high dust loads, although use of biofilters may increase other N losses as N<sub>2</sub>O, NO and N<sub>2</sub>.</td><td></td></tr></table>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /></figure>
Measures related to manure storage and processing

Manure Measure 1: Covered
storage of manure (solid cover and
impermeable base)

Many options are available for covered storage of manure and biogas digestates, including use of metal or concrete tanks with solid lids, floating covers on lagoons and use of slurry bags, most of which are associated with negligible NH₃ emission if well operated. The impermeable base avoids nitrate leaching and must be maintained to avoid leakage.

<figure><img src="image_44.png" /></figure>

Manure Measure 2: Covered
storage of slurry (natural crust and
impermeable base)

Where slurries have a high dry matter content, and stirring is minimized, these may form a natural crust during storage, which is associated with substantially reduced NH₃ emission, although N₂O production may be enhanced. The impermeable base avoids nitrate leaching and must be maintained to avoid leakage.

<figure><img src="image_45.png" /></figure>

Manure Measure 3: Covered
storage of solid manure (dispersed
coverings)

Covering solid manures with dispersed coverings, such as peat, clay, zeolite and phosphogypsum or clay, can substantially reduce NH₃ emissions. The approach works by protecting manure surfaces from the air, while these materials also have a high affinity for ammonium. Sufficient thickness of the covering is required.

<figure><img src="image_46.png" /></figure>

Manure Measure 4: Storage of solid
manure under dry conditions

Simply storing solid manure in a dry place, out of the rain, can also reduce N emissions from a range of N, compounds and N₂. This is even more important for poultry litter, where keeping manure dry limits hydrolysis of uric acid to form NH₃.

<figure><img src="image_47.png" /></figure>

Manure Measure 5: Storage of solid
manure on a solid concrete base
with walls

Storage of manure on a walled solid base helps reduce nitrate leaching and other N leaching by avoiding run-off and infiltration into the soil. The approach costs less than installing a solid cover, but risks substantial NH₃, N₂O, NOₓ and N₂ emissions.

<figure><img src="image_48.png" /></figure>

Manure Measure 6: Slurry mixing
(during storage)

Slurry mixing of stored manure prior to field application helps ensure a homogenous distribution of nutrients. There are no additional benefits to reduce emissions of N₂O, NOₓ or N₂. The method may even increase NH₃ losses (for example, if mixing increases pH by promoting CO₂ loss from slurry), so mixing should only be done shortly before field application.

<figure><img src="image_49.png" /></figure>
<figure><img src="image_50.png" /></figure>

<table><tr><td>Manure Measure 7: Adsorption of slurry ammonium</td><td>Certain additives to slurry can be used to adsorb ammonium on a chemical, physical or biological basis. Mineral additives such as clay/zeolite require a high amount of additives, which can result in the measure being costly (for example, 25 kg of zeolite per m³ slurry to adsorb 55 per cent of ammonium). However, experiments have shown only a small effect in reducing NH₃ emission. Addition of biochar may also reduce NH₃ emissions from stored manure.</td><td></td></tr><tr><td>Manure Measure 8: Slurry acidification (manure storage)</td><td>Ammonia emissions from stored slurry can be reduced by addition of acids. This is most commonly done just prior to spreading. The reduction in pH also reduces CH₄ and is expected to decrease N₂O and N₂ emissions. Acid may be added or produced in situ during storage (for example, by oxidation of atmospheric N₂ augmented using locally produced renewable energy). While feedstock for biogas production can only contain limited amounts of acidified slurry, acidification after anaerobic digestion can help to reduce subsequent NH₃ emissions.</td><td></td></tr><tr><td>Manure Measure 9: Slurry aeration</td><td>Slurry aeration introduces oxygen into the slurry in order to allow aerobic microbes to develop, so reducing odour. However, CO₂ and NH₃ emissions are increased. Emissions of NOₓ are also expected to increase, while greater NO₃⁻ availability risks a subsequent increase in denitrification-related loss of N₂O and N₂. Therefore, slurry aeration is not recommended.</td><td></td></tr><tr><td>Manure Measure 10: Mechanical solid-liquid separation of slurry fractions</td><td>Mechanical separation of solid and liquid fractions of slurry produces an ammonium-rich liquid that degrades more slowly and infiltrates more effectively into soil, reducing NH₃ emissions, with more predictable fertilization benefits increasing crop yields and allowing reduction of mineral N fertilizer. Care is needed to avoid NH₃ and CH₄ losses from the solid fraction, which may serve as a slow-release fertilizer or feedstock for biogas production.</td><td></td></tr><tr><td>Manure Measure 11: Anaerobic digestion</td><td>Anaerobic digestion associated with production of CH₄ biogas reduces emissions of CH₄ from subsequent storage of the digestate, while substituting consumption of fossil energy. Ammonium content and pH in digested slurry are higher than in untreated slurry, increasing the potential for NH₃ emissions, requiring the use of covered stores and low-emission manure spreading. As part of an integrated package of measures, anaerobic digestion can reduce NH₃, N₂O and N₂ losses, while providing an opportunity for advanced forms of nutrient recovery (Nutrient Recovery Measures 3–5). The requirement for an impermeable base avoids nitrate leaching compared with storage of manure on permeable surfaces.</td><td></td></tr></table>

<figure><img src="image_51.png" /></figure>

<figure><img src="image_52.png" /></figure>

<figure><img src="image_53.png" /></figure>

<figure><img src="image_54.png" /></figure>

<figure><img src="image_55.png" /></figure>
## Manure Measure 12: Manure composting

Composting of manure creates a stable and odourless biobased fertilizer product, with lower moisture content, while containing most of the initial nutrients, free of pathogens and seeds. However, losses of NH₃, N₂O, NOₓ, N₂, CO₂ and CH₄ tend to increase, also reducing N fertilizer value, while composting on porous substrates risks increasing N leaching. Use of covered composting can mitigate some of these effects. The UNECE categories shown assume open composting on an impermeable surface.

<figure><img src="image_56.png" /></figure>

## Measures related to nutrient recovery

### Nutrient Recovery Measure 1: Drying and pelletizing of manure solids

Drying and pelleting of solid manures, slurry or digestate solids can be done to create a more stable and odourless biobased fertilizer product. Drying is energy intensive, while NH₃ emissions increase, unless exhaust air filtering or scrubbing and N recovery is applied, or the solids are acidified prior to drying.

<figure><img src="image_57.png" /></figure>

### Nutrient Recovery Measure 2: Combustion, gasification or pyrolysis

Combustion, thermal gasification or pyrolysis of manure and digestate solids can be used to generate a net energy output for heat and/or electricity production. However, the method wastes manure N, which is converted into gaseous N₂ and NOₓ (category 3). Systems under development to minimize N₂ formation and recover the N₂ gases can be considered as category 2 for abating overall N loss.

<figure><img src="image_58.png" /></figure>

### Nutrient Recovery Measure 3: Precipitation of nitrogen salts

Struvite (MgNH₄PO₄·6H₂O) (as well as other phosphorus salts such as hydroxy apatite) can be precipitated from liquid manures, including anaerobically digested slurries and the liquid fraction from digestate separation. The main advantage of struvite compared with other approaches is its high concentration and similarity in physical-chemical properties to conventional mineral N fertilizer. The setting of UNECE category 2 reflects the need for further assessment of efficiencies.

<figure><img src="image_59.png" /></figure>

### Nutrient Recovery Measure 4: Concentration of nitrogen salts and solutions

Mineral concentrates are highly nutrient-rich solutions that may be obtained via ultrafiltration, evaporation or reverse osmosis of the liquid fraction from separation of slurry or digestate. Provided that losses can be kept to a minimum (for example, use of acidification, soil injection), the mineral fertilizer replacement value of the mineral concentrates can be relatively high, as they resemble commercial liquid fertilizers.

<figure><img src="image_60.png" /></figure>
<figure><img src="image_61.png" /></figure>

## **Nutrient Recovery Measure 5: Ammonia stripping and recovery**

In this method, the liquid fraction after manure separation is brought into contact with air, upon which NH₃ evaporates and is collected by a carrier gas. Use of membrane systems allows use of lower temperatures, if membrane fouling can be avoided. Ammonia released from an NH₃ stripping column or from a manure drying facility can be collected using wet scrubbing with an acid solution, such as sulphuric or nitric acid. The ammonium sulfate and nitrate produced can serve as raw materials for mineral fertilizers, providing the opportunity for circular economy development.

<figure><img src="image_62.png" /></figure>

## **C. Field application of organic and inorganic fertilizers, including manures, urine and other organic materials**

55. Measures to reduce nitrogen loss from field application of nitrogen resources are especially important as the benefits of improved nutrient use can be seen by farmers. Measures to reduce overall nitrogen losses thus have a dual aim: to improve resource efficiency (allowing a reduction in bought-in fertilizers and other nutrient resources); and to reduce pollution of air and water, with multiple environmental benefits.

56. According to principle 6 (chapter III) the nitrogen

savings resulting from measures during housing and storage of manure must be accounted for. These actions increase the amounts of nitrogen resources available for field spreading, enabling reductions in newly produced nitrogen resources.

57. The most effective measures are listed below according to applicability:

(a) Measures applicable to both organic and inorganic fertilizers;

(b) Measures applicable to manures and other organic materials;

(c) Measures applicable to inorganic fertilizers;

(d) Measures applicable to livestock grazing; and

(e) Other cropping-related measures. Overall, 20 field measures are identified (see table II.2).

<caption>**Table II.2 :** Measures applicable to organic and inorganic fertilizers, manures and other organic materials and grazing livestock. For explanation of colours see figure II.1</caption>

### Measures applicable to both organic and inorganic fertilizers

#### Field Measure 1: Integrated nutrient management plan

The approach focuses on integrating all the nutrient requirements of arable and forage crops on the farm, through use of all available organic and inorganic nutrient sources. Priority should be given to utilization of available organic nutrient sources first (for example, livestock manure), with the remainder to be supplied by inorganic fertilizers, in accordance with Field Measure 3. Recommendation systems can provide robust estimates of the amounts of N (and other nutrients) supplied by organic manure applications. Supported by soil nutrient testing and decision-support tools to assess crop needs (for example, leaf colour sensing), this information can be used to determine the amount and timing of any additional inorganic fertilizers, while allowing for further input reductions as a result of saved nitrogen from decreased pollution losses.

<figure><img src="image_63.png" /></figure>
<figure><img src="image_64.png" /></figure>

<table><tr><td>Field Measure 2: Apply nutrients at the appropriate rate</td><td>Under application of N will result in reduced crop yields and can lead to mining of soil N and organic matter. Over application of N can also result in reduced crop yields and profits, and surplus available soil N, increasing the risk of losses to air and water. Applying N to match crop requirement at an environmentally and economically sustainable level requires knowledge of the N content of the organic manure or fertilizer product and crop N demand. In-crop soil testing or leaf colour sensing may help with split applications.</td><td></td></tr><tr><td>Field Measure 3: Apply nutrients at the appropriate time</td><td>Targeting N to the soil at times when it is required by an actively growing crop reduces the risks of nitrogen losses to air and water. Multiple (or split) applications reduce the risk of large leaching events and enable later additions to be fine-tuned according to adjustment of yield expectations. Appropriate timing should take account of climatic differences, as well as weather forecasts (for example, to favour manure spreading during cool weather). Combined application of organic slurries and inorganic fertilizer should be avoided where co-occurrence of water and carbon increases N<sub>2</sub>O emissions.</td><td></td></tr><tr><td>Field Measure 4: Apply nutrients in the appropriate form</td><td>This measure mainly targets NH<sub>3</sub> emissions, which are much lower from ammonium nitrate than from urea fertilizer. There is a risk of increased losses through denitrification and/or leaching and run-off because the N saved by decreasing NH<sub>3</sub> emission, unless N application rate is reduced to match the amounts saved (chapter III, principle 6). With organic materials, such as livestock manure, account should be taken of the relative content of inorganic forms of N (such as ammonium) compared with organic compounds, as this affects the N replacement value.</td><td></td></tr><tr><td>Field Measure 5: Limit or avoid fertilizer application in high-risk areas</td><td>Certain areas on the farm can be classified as higher risk in terms of N losses to water, by direct run-off or leaching, or to air through denitrification. Pollution can be reduced by avoiding or limiting fertilizer application to these locations (for example, in the vicinity of ditches and streams and on steeply sloping areas).</td><td></td></tr><tr><td colspan="3">Measures specific to the application of manures and other organic materials</td></tr><tr><td>Field Measure 6: Band spreading and trailing shoe application of livestock slurry</td><td>Reducing the overall surface area of slurry, by application in narrow bands, will lead to a reduction in ammonia emissions of 30-35 per cent compared with surface broadcast application, particularly during the daytime when conditions are generally more favourable for volatilization. In addition, if slurry is placed beneath the crop canopy, the canopy will also provide a physical structure to reduce further the rate of ammonia loss (by 60 per cent).</td><td></td></tr></table>

<figure><img src="image_65.png" /></figure>

<figure><img src="image_66.png" /></figure>

<figure><img src="image_67.png" /></figure>

<figure><img src="image_68.png" /></figure>

<figure><img src="image_69.png" /></figure>
<figure><img src="image_70.png" /></figure>

### Field Measure 7: Slurry injection

Placing slurry in narrow surface slots, via shallow or deep injection greatly reduces the exposed slurry surface area, thereby reducing NH₃ emissions (by 70–90 per cent). Emissions of N₂O (as well as NOₓ and N₂ emissions) may be increased, though this risk can be reduced by compensating for the amount of nitrogen saved through NH₃ emission reductions by using reduced slurry applications rates.

<figure><img src="image_71.png" /></figure>

### Field Measure 8: Slurry dilution for field application

Ammonia losses following surface broadcast slurry application are less for slurries with lower dry matter, because of the more rapid infiltration into the soil. The reduction in ammonia emission will depend on the characteristics of the undiluted slurry and the soil and weather conditions at the time of application (c. 30 per cent emission reduction for 1:1 dilution of slurry in water).

<figure><img src="image_72.png" /></figure>

### Field Measure 9: Slurry acidification (during field application)

A lower pH favours ammoniacal N in solution to be in the form of ammonium rather than ammonia, thereby reducing ammonia volatilization. Typically, sulphuric acid is used to lower the pH, though other acids may be used. Acid addition during field application of slurry requires appropriate safety procedures.

<figure><img src="image_73.png" /></figure>

### Field Measure 10: Nitrification inhibitors (addition to slurry

While more usually associated with mineral fertilizers, nitrification inhibitors can also be added to livestock slurries just prior to application to land with the aim of delaying the conversion of the slurry ammonium content to nitrate, which is more susceptible to Nₐ losses through denitrification, run-off and leaching.<fnref n="6" />

<figure><img src="image_74.png" /></figure>

### Field Measure 11: Rapid incorporation of manures into the soil

Rapid soil incorporation of applied manure (within a few hours after application) reduces the exposed surface area of manure from which NH₃ volatilization occurs and can also reduce N and P losses in run-off. The measure is only applicable to land that is being tilled and to which manure is being applied prior to crop establishment.

<figure><img src="image_75.png" /></figure>

<footnote n="6">⁶ No benefit is expected from using urease inhibitors in spreading cattle and pig manure, as most of the excreted urea will have already hydrolysed to form ammonium during livestock housing and manure storage. Potential long-term effect of nitrification inhibitors on non-target organisms should be considered.</footnote>
Measures specific to the application of inorganic fertilizers

Field Measure 12: Replace urea with an alternative N fertilizer

Following land application, urea will undergo hydrolysis to form ammonium carbonate, locally increasing pH and favouring NH₃ emission. By contrast, for fertilizer forms such as ammonium nitrate, ammonium will be in equilibrium at a much lower pH, greatly reducing the potential for ammonia volatilization. In calcareous and semi-arid soils, the replacement of urea by ammonium nitrate or calcium ammonium nitrate usually also leads to the abatement of N₂O and NOₓ, though the opposite can happen in other situations.

<figure><img src="image_76.png" /></figure>

Field Measure 13: Urease inhibitors

Urease inhibitors slow the hydrolysis of urea by inhibiting the urease enzyme in the soil. This allows more time for urea to be incorporated in the soil and for plant uptake, thereby reducing the potential for NH₃ emissions. In some studies (for example, under nitrifying conditions), urease inhibitors have also been found to decrease soil N₂O and NOₓ emissions.<fnref n="7" />

<figure><img src="image_77.png" /></figure>

Field Measure 14: Nitrification inhibitors with inorganic fertilizers

Nitrification inhibitors are chemicals (manufactured or natural) that can be incorporated into NH₃ or urea-based fertilizer products, to slow the rate of conversion of ammonium to nitrate. These have been shown to reduce emissions of N₂O and can also be expected to reduce emissions of NOₓ and N₂, and leaching losses of nitrate, as they arise from the same process pathways. Potential long-term effects of nitrification inhibitors on non-target organisms should be considered. Field Measures 13 and 14 are complementary and can be combined.

<figure><img src="image_78.png" /></figure>

Field Measure 15: Controlled release fertilizers

Special coatings on fertilizers slow the release of nutrients to the soil over a period of several months (for example, sulphur or polymer coating). The gradual release of nutrients is associated with lower leaching and gaseous N losses. Organic N products with low water solubility, such as isobutylidene diurea (IBDU), crotonylidene diurea (CDU) and methylene-urea polymers, are also considered as slow-release fertilizers. Potential effects from the degradation of polymer coatings to form microplastics remain to be demonstrated.

<figure><img src="image_79.png" /></figure>

Field Measure 16: Fertigation

In areas subject to drought or limited soil water availability, the efficiency of water and N use should be managed in tandem. Drip irrigation combined with split application of fertilizer N dissolved in the irrigation water (for example, drip fertigation) provides precision application (in space and time), minimizing evaporative losses of water and losses of N to air and water, thereby greatly enhancing the N use efficiency.

<figure><img src="image_80.png" /></figure>

<footnote n="7">7 See footnote 6.</footnote>
<figure><img src="image_81.png" /></figure>

**Field Measure 17: Precision placement of fertilizers, including deep placement**

Placement of N and P fertilizer directly into the soil close to the rooting zone of the crop can be associated with enhanced N and P uptake, lower losses of N to air and N and P to water and a lower overall N and P requirement compared with broadcast spreading. Placement within the soil reduces losses by NH₃ volatilization.

<figure><img src="image_82.png" /></figure>

**Measures for grazing livestock**

**Field Measure 18: Extend the grazing season**

Ammonia emissions arising from grazing livestock are much smaller than for managed manure (for example, from housed animals) because of the rapid infiltration of urine into the soil. Where climate and soil conditions allow, extending the grazing season will result in a higher proportion of excreta being returned via dung and urine during grazing, thereby reducing NH₃ emissions. Risks of nitrate leaching and denitrification losses (as N₂O and N₂) may be increased unless additional actions are taken.

<figure><img src="image_83.png" /></figure>

**Field Measure 19: Avoid grazing in high-risk areas**

High-risk areas include those with high connectivity to vulnerable surface waters and/or groundwaters, and those subject to waterlogging, poaching and compaction. These include cases with both greatly enhanced potential for N, P and pathogen losses from dung and urine via run-off and denitrification. Such areas should be fenced, or carefully managed, to exclude livestock grazing.

<figure><img src="image_84.png" /></figure>

**Field Measure 20: Nitrification inhibitors: addition to urine patches**

Nitrification inhibitors, more commonly associated with mineral fertilizers, may also have an application in reducing leaching and denitrification from urine patches in grazed pastures. Risks of increased NH₃ emissions from urine patches associated with delays in nitrification are likely to be minimal because of the rapid urine infiltration.

<figure><img src="image_85.png" /></figure>

## D. Land-use and landscape management

58. Landscape management enables N pollution problems to be addressed where they occur, both in space and time, helping to achieve the desired N mitigation effect.

59. Landscape measures can be economically favourable compared with other types of measures, especially as they can be placed outside agricultural areas, for example, retaining agricultural production, while creating new nature and recreational resources in the form of hedgerows, forests and extensive buffer-zones around fields, streams or wetlands.

60. For land-use and landscape-scale measures, the primary focus is on mitigation of adverse impacts, though there can also be benefits for emissions abatement. This means that measures focus on increasing overall landscape resilience so that there are fewer adverse impacts per unit of emission, in addition to a contribution to reducing emissions (for example, by local recapture within landscapes).

61. The most effective measures are listed in table II.3 according to their applicability. Overall, 16 Landscape Measures are identified.
<table><caption>**Table II.3 :** Measures related to land-use and landscape management. For explanation of colours see figure II.1.</caption><thead><tr><th colspan="2">Land-use measures for crops and crop rotations, including agroforestry</th></tr></thead><tbody><tr><td>Landscape Measure 1: Increasing land cover with perennial crops</td><td>Introducing perennial crops, such as grasslands, predominately grass or grass-clover mixtures, can reduce the risk of environmental N<sub>r</sub> losses due to N<sub>r</sub> immobilization in plant biomass and litter. They typically have a higher capacity for storage in biomass/litter and have a longer N uptake period than annual plants. This approach also increases soil N (and C) stocks, with higher soil organic carbon contents providing increased N<sub>r</sub> retention capacities.</td></tr><tr><td>Landscape Measure 2: Use of cover crops in arable rotations</td><td>Cover crops (or "catch crops") that follow the main crop can help reduce available soil N levels during high-risk periods for nitrate leaching by taking up N originating from post-harvest decomposition and mineralization. Success in reducing emissions and in increasing N use efficiency over the whole cropping cycle depends on effective management of the cover crop residue and appropriate tuning of fertilization rates to the subsequent crop. The approach also reduces the risk of erosion and other soil/nutrient transport to streams.</td></tr><tr><td>Landscape Measure 3: Inclusion of N<sub>2</sub>-fixing plants in crop rotations (including intercropping)</td><td>Inclusion of plants such (for example, legumes) that fix atmospheric N<sub>2</sub> to produce organic nitrogen forms reduces the requirement for applied N (as fertilizer or manure) and the N losses associated with such applications. The approach can be implemented by including legumes as part of a crop rotation or by including legumes within a mixed crop ("intercropping", for example grass-clover sward). Incorporation of legumes into the soil as part of a crop rotation leads to a pulse of mineralization, which can lead to N<sub>r</sub> emissions to air and nitrate leaching to water.</td></tr><tr><td>Landscape Measure 4: Introducing agroforestry and trees in the landscape</td><td>Introducing agroforestry land-uses, with alternate rows of trees and annual crops or blocks of trees in the landscape, can help remove surplus N<sub>r</sub> from neighbouring arable fields, minimizes erosion, provides wind shelter, and supports biodiversity provision.</td></tr><tr><td colspan="2">Landscape measures for management of riparian areas and waters</td></tr><tr><td>Landscape Measure 5: Constructed wetlands for stimulating N<sub>r</sub> removal</td><td>Constructed wetlands can help remove nutrients from water bodies or for wastewater treatment. The principle of operation of constructed wetlands is to encourage conditions that favour denitrification to N<sub>2</sub>, while other nutrients accumulate. The approach is cheap but wastes N<sub>r</sub> as N<sub>2</sub> and risks increased N<sub>2</sub>O and CH<sub>4</sub> emissions, as well as dissolved organic C and N loss to watercourses.</td></tr></tbody></table>

<figure><img src="image_86.png" /></figure>

<figure><img src="image_87.png" /></figure>

<figure><img src="image_88.png" /></figure>

<figure><img src="image_89.png" /></figure>

<figure><img src="image_90.png" /></figure>
<figure><img src="image_91.png" /></figure>

<table><tr><td>Landscape Measure 6: Planting of paludal cultures in riparian areas or constructed wetlands</td><td>Wetland (paludal) plants are specifically planted to maximize biomass growth, thereby removing Nr from the water. The biomass can be harvested and used, for example, as source of bioenergy. Poorly managed systems may increase N2O and N emissions (as well as CH4 emissions) if Nr is not fully used for plant growth. Performance is compared with Landscape Measure 5 as the reference.</td><td></td></tr><tr><td>Landscape Measure 7: Use of organic layers to promote nitrate removal</td><td>A layer of organic matter (for example, woodchips) is placed in trenches in soil at key points in the landscape to promote denitrification, enhancing the removal of nitrates from groundwaters and surface waters. The approach can help improve water quality but wastes Nr resources as N2 emission while risking increased N2O and CH4 emissions.</td><td></td></tr><tr><td>Landscape Measure 8: Drainage management</td><td>Drainage measures (such as insertion of tile drains for water-table management) promote run-off and limit waterlogging, reducing residence times of nutrients. This can help abate emissions of CH4 and N compounds relating to denitrification (N2O, N2), while shorter residence time may increase NO3- and carbon losses to stream waters.</td><td></td></tr><tr><td>Landscape Measure 9: Stimulating Nr removal in coastal waters</td><td>It has been proposed that growing seaweed, eel grass, and oyster farming or shellfish aquaculture can help remove excess nutrients from coastal waters. Nitrogen is incorporated into the biomass, which is harvested. While the principle of encouraging Nr recovery into useful products is sound, further evidence of the quantitative performance of this system is needed before it can be used with confidence to mitigate coastal water pollution.</td><td></td></tr><tr><td colspan="3"><strong>Afforestation, set-aside and hedgerow measures to mitigate Nr effects</strong></td></tr><tr><td>Landscape Measure 10: Introducing trees for afforestation and hedgerows in the landscape</td><td>Afforestation and preservation and planting of strips of trees around agricultural fields can reduce NO3- leaching and has very positive effects on biodiversity. The efficacy of hedgerows for Nr retention will depend on size and placement of hedgerows, on the amount of NO3- in soil and groundwater, hydrological flow-paths and timing. With sufficient tree area, there can also be benefits for NH3 mitigation (see Landscape Measure 12).</td><td></td></tr><tr><td>Landscape Measure 11: Set-aside and other unfertilized grassland</td><td>Unfertilized grasslands (for example, "set-aside" grassland) have the potential to remove NO3- from lateral soil water flows and can be used as buffers to protect adjacent natural land or streams. The effectiveness of the measure also depends on the extent to which overall N inputs are accordingly reduced in the landscape.</td><td></td></tr></table>

<figure><img src="image_92.png" /></figure>

<figure><img src="image_93.png" /></figure>

<figure><img src="image_94.png" /></figure>

<figure><img src="image_95.png" /></figure>

<figure><img src="image_96.png" /></figure>

<figure><img src="image_97.png" /></figure>
## Mitigating the cascade of N, effects from livestock hot spots

**Landscape Measure 12: Shelterbelts around large point sources**

Wide shelterbelts, such as woodland planted around point sources, can help mitigate landscape N, dispersion from emission hot spots, such as manure storage areas or animal housing facilities, due to the function of trees as biofilters for NH₃ and the immobilization of N, into plant biomass and soil organic N stocks. The approach may also reduce NO₃⁻ leaching losses but can risk increased N₂O emissions.

<figure><img src="image_98.png" /></figure>

**Landscape Measure 13: Environmentally smart placement of livestock facilities and outdoor animals**

Placement of livestock facilities away from sensitive terrestrial habitats or waterbodies can reduce local N, problems. The approach is most commonly used as part of planning procedures for new developments to expand existing farms.

<figure><img src="image_99.png" /></figure>

## Smart landscape farming in relation to mitigation of N, effects

**Landscape Measure 14: Digital planning of land-use on basis of a suitability assessment**

Land-use and farm planning based on digital 3D precision maps of soil N retention can help to optimize fertilizer use and reduce N leaching and other losses. This can help to improve nutrient retention at landscape scale, improve water quality in surface waters and groundwaters and reduce gaseous N, losses. The approach typically requires support through detailed modelling.

<figure><img src="image_100.png" /></figure>

**Landscape Measure 15: Towards mixed farming**

Mixed farming combines livestock and cropping at farm and landscape scales. Crop and livestock integration provides opportunities to connect nitrogen inputs and surpluses so as to reduce overall levels of nitrogen pollution, while increasing farm- and landscape-scale nitrogen use efficiency. Emissions associated with long-distance feed and manure transport are reduced. Mixed cropping-livestock systems also provide the opportunity to develop free-range livestock production in combination with crops that mitigate N, losses.

<figure><img src="image_101.png" /></figure>

**Landscape Measure 16: Landscape-level targeting of technical options to reduce N, losses**

Technical measures may be selectively applied at the landscape scale, where they are targeted to be used in specific sensitive areas. Analysis at the landscape scale can also allow for a more nuanced analysis of the potential trade-offs and synergies between emissions abatement and effects mitigation of different N compounds.

<figure><img src="image_102.png" /></figure>
<figure><img src="image_103.png" /></figure>

## E. Overall priorities for policymakers

62. Policymakers may find it helpful to recognize that underlying every measure is one or more of the listed principles for integrated sustainable nitrogen management, as illustrated by table II.4.

63. The following priorities are identified linked to livestock housing and manure storage:

(a) Concepts for best practices to reduce adverse environmental impacts require integrated concepts including consideration of the interactions:

(i) Between pollutants;

(ii) With animal welfare aspects;

(iii) With climate change;

(iv) With biodiversity protection; and

(v) With region-specific characteristics.

(b) Concepts to reduce adverse environmental impacts require a detailed understanding at a process level to assess emissions, influencing factors and abatement/mitigation options;

(c) Concepts to reduce adverse environmental impacts depend on the development of flexible concepts that account for climate- and site-specific conditions, the three pillars of sustainability, potential conflicts of interest and whole-system solutions.

<table><caption>**Table II.4:** Summary of measures to support integrated sustainable nitrogen management in agriculture and their linkage to underlying principles</caption><thead><tr><th>Measure numbers</th><th>Description of measures</th><th>Principle numbers</th><th>Description and application of the principles</th></tr></thead><tbody><tr><td colspan="4">Livestock Diets, Housing, Manure Management &amp; Nutrient Recovery</td></tr><tr><td rowspan="3">Dietary Measures 1, 4 and 5</td><td rowspan="3">Adapt protein intake in diet (cattle, pigs, poultry)</td><td>Principle 5</td><td>Control of N inputs influences all N loss pathways.</td></tr><tr><td>Principle 22</td><td>Dietary strategies for N consider C and CH<sub>4</sub> interactions.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td>Dietary Measure 2</td><td>Increase productivity (dairy and beef cattle)</td><td>Principle 13</td><td>Optimizing animal production requires that all factors be in balance.</td></tr><tr><td>Dietary Measure 3</td><td>Increase longevity (dairy cattle)</td><td>Principle 13</td><td>Optimizing animal production requires that all factors be in balance</td></tr><tr><td rowspan="2">Housing Measure 1 and Manure Measure 10</td><td rowspan="2">Immediate segregation of urine and faeces (cattle). Mechanical separation</td><td>Principle 14</td><td>Reduce rate of urea hydrolysis.</td></tr><tr><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air by increasing infiltration to soil.</td></tr><tr><td>Housing Measures 2, 3, 9 and 10</td><td>Reduce emitting surface and regular cleaning of floors (cattle, pigs)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, including by reducing temperature.</td></tr><tr><td>Housing Measures 4 and 11</td><td>Frequent slurry removal (cattle, pigs)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, plus benefits through reducing temperature and surface area.</td></tr><tr><td>Housing Measures 5 and 12</td><td>Increase bedding material (cattle and pigs with solid manure)</td><td>Principle 7</td><td>Nitrogen input-output balance, with increased storage from N absorbed in bedding.</td></tr><tr><td>Housing Measures 6 and 13</td><td>Barn climatization (cattle, pigs)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, due to reduced temperature and airflow.</td></tr></tbody></table>
<table><thead><tr><th>Measure numbers</th><th>Description of measures</th><th>Principle numbers</th><th>Description and application of the principles</th></tr></thead><tbody><tr><td>Housing Measures 7, 14 and 17</td><td>Acid air-scrubbers (cattle, pigs, poultry)</td><td>Principle 7</td><td>Nitrogen input-output balance, with N captured by the scrubbers.</td></tr><tr><td>Housing Measure 8</td><td>Slurry acidification (pig and cattle)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, due to reduced pH.</td></tr><tr><td rowspan="3">Housing Measures 15 and 18</td><td rowspan="3">Biological air-scrubbers (pigs and poultry)</td><td>Principle 7</td><td>Nitrogen input-output balance, with N captured by the scrubbers.</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="2">Housing Measure 16</td><td rowspan="2">Rapid drying of poultry litter</td><td>Principle 14</td><td>Reduce rate of urea hydrolysis.</td></tr><tr><td>Principle 16</td><td>Reduce rate of nitrification.</td></tr><tr><td rowspan="2">Manure Measure 1</td><td rowspan="2">Covered storage (solid cover and impermeable base)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td>Principle 20</td><td>Coupling N and water cycles: avoidance of rain driven leaching and run-off from stored manure.</td></tr><tr><td rowspan="4">Manure Measure 2</td><td rowspan="4">Covered slurry storage (natural crust and impermeable base)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td>Principle 20</td><td>Coupling N and water cycles: avoidance of rain driven leaching and run-off from stored manure.</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="2">Manure Measure 3</td><td rowspan="2">Covered storage of solid manure (dispersed coverings)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE. May be combined with Manure Measure 5.</td></tr><tr><td rowspan="2">Manure Measure 4</td><td rowspan="2">Storage of solid manure under dry conditions</td><td>Principle 16</td><td>Reduced rate of nitrification and denitrification.</td></tr><tr><td>Principle 20</td><td>Coupling N and water cycles: avoidance of rain driven leaching and run-off from stored manure.</td></tr><tr><td rowspan="4">Manure Measure 5</td><td rowspan="4">Storage of manure on a concrete base with walls</td><td>Principle 20</td><td>Coupling N and water cycles: avoidance of rain driven leaching and run-off from stored manure.</td></tr><tr><td>contra Principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="2">Manure Measure 6</td><td rowspan="2">Slurry mixing</td><td>Principle 9</td><td>Managing spatial variations: better mixed slurry ensures more reliable application rate.</td></tr><tr><td>contra Principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>Manure Measure 7</td><td>Additives to adsorb slurry ammonium</td><td>Principle 7</td><td>Nitrogen input-output balance, with increased storage from N absorbed in bedding.</td></tr><tr><td>Manure Measure 8</td><td>Slurry acidification</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, due to reduced pH.</td></tr></tbody></table>
<figure><img src="image_104.png" /></figure>

<table><thead><tr><th>Measure numbers</th><th>Description of measures</th><th>Principle numbers</th><th>Description and application of the principles</th></tr></thead><tbody><tr><td rowspan="3">Manure Measure 9</td><td rowspan="3">Slurry aeration to reduce odour</td><td>contra Principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="5">Manure Measure 11</td><td rowspan="5">Anaerobic digestion of manure</td><td>Principle 6</td><td>Measures to save N pollution leave more available in the farming system, which needs to be managed accordingly.</td></tr><tr><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td>Principle 16</td><td>Reduce rate of nitrification.</td></tr><tr><td>Principle 18</td><td>Can increase whole system NUE by promoting N recovery and reuse.</td></tr><tr><td>Principle 19</td><td>Co-benefits from reuse of other nutrients and CH<sub>4</sub>.</td></tr><tr><td rowspan="4">Manure Measure 12</td><td rowspan="4">Manure composting for odourless fertilizer supply</td><td>Principle 19</td><td>Co-benefits from reuse of other nutrients.</td></tr><tr><td>contra Principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="3">Nutrient Recovery Measure 1</td><td rowspan="3">Drying and pelletizing of manure solids</td><td>Principle 19</td><td>Co-benefits from reuse of other nutrients.</td></tr><tr><td>contra Principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="4">Nutrient Recovery Measure 2</td><td rowspan="4">Combustion, gasification or pyrolysis</td><td>Principle 4</td><td>Trade-offs require policy priorities to be set (for example, bioenergy or N pollution).</td></tr><tr><td>contra Principle 6</td><td>Burning destroys N resources, reducing system-wide NUE (unless converted into a recoverable N<sub>r</sub> form).</td></tr><tr><td>contra Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 6</td><td>Measures to save N pollution leave more N available for the farming system, which needs to be managed accordingly.</td></tr><tr><td rowspan="3">Nutrient Recovery Measures 3 and 4</td><td rowspan="3">Precipitation of N salts. Concentration of N solutions.</td><td>Principle 18</td><td>Increase whole-system NUE by promoting N recovery and reuse.</td></tr><tr><td>Principle 19</td><td>Co-benefits from reuse of other nutrients.</td></tr><tr><td></td><td></td></tr></tbody></table>
<table><thead><tr><th>Measure numbers</th><th>Description of measures</th><th>Principle numbers</th><th>Description and application of the principles</th></tr></thead><tbody><tr><td rowspan="3">Nutrient Recovery Measure 5</td><td rowspan="3">Ammonia stripping and recovery</td><td>Principle 6</td><td>Measures to save N pollution leave more N available in the farming system, which needs to be managed accordingly.</td></tr><tr><td>Controlled use of principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air with high pH and temperature increases emission of NH<sub>3</sub> (which is re-captured).</td></tr><tr><td>Principle 18</td><td>Increase whole system NUE by promoting N recovery and reuse.</td></tr><tr><td colspan="4"><strong>Field application</strong></td></tr><tr><td rowspan="7">Field Measure 1</td><td rowspan="7">Integrated nutrient management plan</td><td>All principles apply including:</td><td></td></tr><tr><td>Principle 2</td><td>Multiple actors have a role in N management: a clearly documented plan can support multi-actor agreement.</td></tr><tr><td>Principle 5</td><td>Control of N inputs influences all N loss pathways.</td></tr><tr><td>Principle 6</td><td>Measures to save N pollution leave more N available in the farming system, which needs to be managed accordingly.</td></tr><tr><td>Principle 7</td><td>Nitrogen input-output balance provides a basis to optimize N and economics.</td></tr><tr><td>Principle 8</td><td>Matching inputs to crop and livestock needs allows all N losses to be reduced.</td></tr><tr><td>Principle 9</td><td>Spatially explicit management to match N needs and vulnerability within and between fields.</td></tr><tr><td rowspan="4">Field Measures 2 and 3</td><td rowspan="4">Apply nutrients at appropriate rate and time</td><td>Principle 5</td><td>Control of N inputs influences all N loss pathways.</td></tr><tr><td>Principle 6</td><td>Measures to save N pollution leave more N available in the farming system, which needs to be managed accordingly.</td></tr><tr><td>Principle 7</td><td>Nitrogen input-output balance provides a basis to optimize N and economics.</td></tr><tr><td>Principle 8</td><td>Matching inputs to crop & livestock needs allows all N losses to be reduced.</td></tr><tr><td rowspan="3">Field Measure 4</td><td rowspan="3">Apply nutrients in the appropriate form</td><td>Principle 14</td><td>Reduce rate of urea hydrolysis.</td></tr><tr><td>Principle 16</td><td>Reduce rate of nitrification.</td></tr><tr><td>Principle 17</td><td>Nitrogen input forms reducing N<sub>2</sub>O loss may also reduce N<sub>2</sub> loss, as both are controlled by denitrification.</td></tr><tr><td rowspan="2">Field Measure 5</td><td rowspan="2">Limit or avoid fertilizer use in high-risk areas</td><td>Principle 9</td><td>Spatial variations in agricultural land require spatially explicit N management.</td></tr><tr><td>Principle 10</td><td>Spatial variations in natural habitat sensitivity require spatially explicit N management.</td></tr><tr><td rowspan="2">Field Measure 6</td><td rowspan="2">Band-spreading and trailing shoe application of slurry</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td>Principle 6</td><td>Measures to save N pollution leave more N available in the farming system, which needs to be managed accordingly.</td></tr></tbody></table>
<figure><img src="image_105.png" /></figure>

<table><thead><tr><td>Measure numbers</td><td>Description of measures</td><td>Principle numbers</td><td>Description and application of the principles</td></tr></thead><tbody><tr><td rowspan="2">Field Measures 7 and 11</td><td>Slurry injection</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td>Rapid incorporation of manure</td><td>Principle 6</td><td>Measures to save N pollution leave more N available in the farming system, which needs to be managed accordingly.</td></tr><tr><td rowspan="3">Field Measure 8</td><td rowspan="3">Slurry dilution for field application</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air by increasing infiltration to soil.</td></tr><tr><td>Principle 20</td><td>Coupling N and water cycles: may risk increased NO<sub>3</sub><sup>-</sup> leaching unless integrated with irrigation management.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td>Field Measure 9</td><td>Slurry acidification (during spreading)</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air by decreasing pH.</td></tr><tr><td rowspan="2">Field Measures 10, 14 and 20</td><td rowspan="2">Nitrification inhibitors (slurry, fertilizers and urine)</td><td>Principle 16</td><td>Reducing rate of nitrification and denitrification reduces N losses and increases NUE.</td></tr><tr><td>Principle 17</td><td>Reducing N<sub>2</sub>O loss may also reduce N<sub>2</sub> loss.</td></tr><tr><td>Field Measure 12</td><td>Replace urea with other N fertilizer</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air by avoiding pH peaks associated with urea hydrolysis.</td></tr><tr><td>Field Measure 13</td><td>Urease inhibitors: addition to urea-based fertilizers</td><td>Principle 14</td><td>Reduce rate of urea hydrolysis.</td></tr><tr><td>Field Measure 15</td><td>Slow release fertilizers</td><td>Principle 8</td><td>Matching N inputs to crop needs, through improved timing of N availability.</td></tr><tr><td>Field Measure 16</td><td>Fertigation</td><td>Principle 20</td><td>Co-optimization of N and water increases effective nutrient uptake reducing N losses.</td></tr><tr><td rowspan="2">Field Measure 17</td><td rowspan="2">Precision placement of fertilizer including deep placement</td><td>Principle 12</td><td>Optimizing crop yield and NUE requires that all defining and limiting factors be addressed simultaneously.</td></tr><tr><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air.</td></tr><tr><td rowspan="3">Field Measure 18</td><td rowspan="3">Extended grazing season</td><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, as urine infiltrates soil more rapidly than manures and slurries.</td></tr><tr><td>Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="2">Field Measure 19</td><td rowspan="2">Avoid grazing high-risk areas for waterlogging and run-off</td><td>Principle 9</td><td>Spatial variations in agricultural land require spatially explicit N management.</td></tr><tr><td>Principle 10</td><td>Spatial variations in natural habitat sensitivity require spatially explicit N management.</td></tr></tbody></table>
<table><thead><tr><th>Measure numbers</th><th>Description of measures</th><th>Principle numbers</th><th>Description and application of the principles</th></tr></thead><tbody><tr><td colspan="4"><strong>Land-use and landscape management</strong></td></tr><tr><td rowspan="3">Landscape Measure 1</td><td rowspan="3">Increasing land cover with perennial crops</td><td>Principle 7</td><td>Perennial crops allow more C and N to be stored in biomass and soil, reducing N losses according to the mass balance of inputs-outputs.</td></tr><tr><td>Principle 16</td><td>Reduction in soil inorganic N levels can reduce losses as NO<sub>3</sub><sup>-</sup>, NO<sub>x</sub>, N<sub>2</sub>O and N<sub>2</sub>.</td></tr><tr><td>Principle 20</td><td>Better-developed root systems of perennial crops may offer co-benefits for N and water to reduce NO<sub>3</sub><sup>-</sup> leaching.</td></tr><tr><td rowspan="4">Landscape Measure 2</td><td rowspan="4">Use of cover crops in arable rotations</td><td>Principle 7</td><td>Removing N using a cover crop (or catch crop) can reduce N loss during vulnerable periods.</td></tr><tr><td>Principle 8</td><td>Matching N inputs to crop needs, offers opportunity to reduce all N losses.</td></tr><tr><td>Principle 16</td><td>Cover crops remove N from the soil and can therefore reduce losses as NO<sub>3</sub><sup>-</sup>, NO<sub>x</sub>, N<sub>2</sub>O and N<sub>2</sub>.</td></tr><tr><td>Principle 20</td><td>Co-optimizing N and water management can help reduce NO<sub>3</sub><sup>-</sup> leaching.</td></tr><tr><td rowspan="4">Landscape Measure 3</td><td rowspan="4">Inclusion of N<sub>2</sub> fixing plants in crop rotations (including intercropping)</td><td>Principle 8</td><td>Matching N inputs to crop needs, offers opportunity to reduce all N losses.</td></tr><tr><td>Principle 15</td><td>Reduce exposure of NH<sub>4</sub><sup>+</sup>-containing resources to air, by provision of slow release biological N fixation.</td></tr><tr><td>Principle 16</td><td>Decreasing denitrification reduces other N losses by a slow-release N source.</td></tr><tr><td>Principle 16</td><td>Ploughing-in of N from legumes in crop-rotations manure may give N losses as NO<sub>3</sub><sup>-</sup>, NO<sub>x</sub>, N<sub>2</sub>O and N<sub>2</sub>.</td></tr><tr><td rowspan="3">Landscape Measure 4</td><td rowspan="3">Introducing agroforestry and trees into the landscape</td><td>Principle 7</td><td>Perennial crops allow more C and N to be stored in biomass and soil, reducing N losses according to the mass balance of inputs-outputs.</td></tr><tr><td>Principle 11</td><td>The structure of landscape elements affects the capacity to store and buffer nitrogen flows.</td></tr><tr><td>Principle 20</td><td>Better-developed root systems of perennial crops may offer co-benefits for N and water to reduce NO<sub>3</sub><sup>-</sup> leaching.</td></tr><tr><td rowspan="5">Landscape Measure 5</td><td rowspan="5">Constructed wetlands</td><td>Principle 11</td><td>Specially designed ecosystems may act as buffers of N pollution.</td></tr><tr><td>Principle 19</td><td>Co-benefits if reuse of other nutrients.</td></tr><tr><td>Principle 15</td><td>Exposure of NH<sub>4</sub><sup>+</sup> resources to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="4">Landscape Measure 6</td><td rowspan="4">Planting of paludal cultures in riparian areas or constructed wetlands</td><td>Principle 11</td><td>The structure of landscape elements affects the capacity to store and buffer nitrogen flows.</td></tr><tr><td>Principle 15</td><td>Exposure to air increases NH<sub>3</sub> emissions.</td></tr><tr><td>Principle 16</td><td>Increasing denitrification risks other N losses and reduced NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr></tbody></table>
<figure><img src="image_106.png" /></figure>

<table><thead><tr><td>Measure numbers</td><td>Description of measures</td><td>Principle numbers</td><td>Description and application of the principles</td></tr></thead><tbody><tr><td rowspan="2">Landscape Measure 7</td><td rowspan="2">Use of organic layers to promote nitrate removal</td><td>contra Principle 16</td><td>Deliberately increasing denitrification reduces NO<sub>3</sub><sup>-</sup> in water flows while increasing other N losses as N<sub>2</sub>O and N<sub>2</sub>, also reducing NUE.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td rowspan="2">Landscape Measure 8</td><td rowspan="2">Drainage management</td><td>Principle 16</td><td>Reduces denitrification related losses by reducing soil water residence times, but correspondingly likely to increase NO<sub>3</sub><sup>-</sup> losses to stream-water.</td></tr><tr><td>Principle 4</td><td>Trade-offs require policy priorities to be set.</td></tr><tr><td>Landscape Measure 9</td><td>Stimulating N<sub>r</sub> removal in coastal waters</td><td>Principle 7</td><td>Cultivation and harvesting of biomass in coastal waters allows more N removed reducing coastal N pollution according to mass balance.</td></tr><tr><td rowspan="2">Landscape Measure 10</td><td rowspan="2">Introducing trees for afforestation and hedgerows</td><td>Principle 11</td><td>The structure of landscape elements affects the capacity to store and buffer nitrogen flows.</td></tr><tr><td>Principle 20</td><td>Better-developed root systems of perennial crops may offer co-benefits for N and water management to reduce NO<sub>3</sub><sup>-</sup> leaching.</td></tr><tr><td>Landscape Measure 11</td><td>Set-aside and other unfertilized grassland</td><td>Principle 11</td><td>The structure of landscape elements affects the capacity to store and buffer nitrogen flows. Unfertilized land may serve as a buffer to N compounds flowing to water, and physically separate emissions and vulnerable ecosystems.</td></tr><tr><td>Landscape Measure 12</td><td>Shelterbelts of trees around large point sources</td><td>Principle 11</td><td>The structure of landscape elements affects the capacity to store and buffer nitrogen flows. Tree belts planted around point sources of NH<sub>3</sub> emission help recapture and disperse NH<sub>3</sub> and particles, acting as buffers to protect nearby sensitive ecosystems.</td></tr><tr><td rowspan="2">Landscape Measure 13</td><td rowspan="2">Environmentally smart placement of livestock facilities</td><td>Principle 11</td><td>The structure of landscape elements affects the capacity to store and buffer nitrogen flows. Utilizes smart placement to maximize landscape buffering capability.</td></tr><tr><td>Principle 16</td><td>Avoiding acute N inputs to semi-natural lands helps avoid local surpluses, reducing N losses.</td></tr><tr><td>Landscape Measure 14</td><td>Digital planning of land-use suitability</td><td>Principles 11, 12, 14, 16 and 20</td><td>Optimizing crop and livestock production according to all parameters including landscape structure and vulnerability, including interactions with water flows.</td></tr><tr><td>Landscape Measure 15</td><td>Towards mixed farming, including free-range systems</td><td>Principles 5, 7 and 8</td><td>Mixed farming allows manure flows to be reused more locally in cropping systems, allowing reduced N inputs according to mass balance with a broad opportunity to reduce N losses.</td></tr><tr><td>Landscape Measure 16</td><td>Landscape-level targeting of technical options to reduce N<sub>r</sub> loss</td><td>Principle 4 and Principle 11</td><td>Based on agreed policy priorities, certain areas are designated as more vulnerable and requiring special protection, so more ambitious technical measures are applied in the vicinity of such sites.</td></tr></tbody></table>

Abbreviations: NUE, nitrogen use efficiency, which may be defined on a range of scales from crop and livestock scale to the full agrifood chain and across the entire economy.
<figure><img src="image_107.png" /></figure>

64. The priority considerations for policymakers regarding integrated management of N to minimize pollution include:

(a) Integrated N planning at the farm, sectoral and regional levels (including addressing the trend towards concentration of intensive livestock and crop farms, often near cities), taking into account the fact that a healthy mix of food products is produced at low environmental burden;

(b) Minimizing nutrient applications to high-risk zones (water and N deposition-sensitive habitats, high-risk drainage basins), being aware of region-specific requirements and conditions;

(c) Integrating nutrients from recycling of organic residues to agriculture (this may require regional planning and adequate quality control of materials to be applied);

(d) Identifying cost-effective abatement measures for farmer implementation;

(e) Providing technical advice, guidance and adequate training to farm advisors and farmers relative to N use and management.

65. Priority considerations for policymakers regarding land-use and landscape actions for integrated nitrogen management include:

(a) Establishing pilots and demonstrations of sustainable land-use and landscape management to demonstrate how these approaches can utilize the nitrogen cycle to maximize overall resilience with reduced environmental impacts;

(b) Establishing evidence, scenarios and tools to demonstrate performance in reducing multiple adverse effects of nitrogen on sensitive landscapes, including analysis of costs and benefits;

(c) Demonstrating how land-use and landscape options support the development of production systems that are more resilient to climate change and with more diverse services delivered, at the same time as reducing environmental N footprint;

(d) Consideration of how benefits for nitrogen link to other issues; for example, woodlands in landscapes serve many functions, such as increasing landscape water retention to reduce flooding and providing wildlife habitats and shelter for livestock, in addition to their benefit as N management tools.

## F. Priorities for practitioners

66. The following priorities are identified linked to livestock housing and manure storage:

(a) Match the N content of the animals' diet as closely as possible to the animals' requirements in order to avoid excess N input already at the feeding level;

(b) Keep livestock houses cool and clean and regularly remove manure to a covered outside storage;

(c) Store manure in a covered store, consider manure treatment for low emissions (for example, anaerobic digestion, separation, acidification);

(d) Recycle manure nutrients as valuable fertilizer in crop production.

67. For farmers, the main goals of implementing abatement measures are to increase the efficiency of N applied as fertilizer or manure to their crops, save costs on nitrogen inputs, and reduce pollution into air, water and soil. As such, the top field measures for farmers to improve N use efficiency are considered to be:

(a) Integrated farm-scale N management planning taking account of all available N sources;

(b) Precision nutrient management: appropriate rate, timing, form and placement of N;

(c) Use of the appropriate fertilizer product and form (including inhibitors, as relevant) in the appropriate context;

(d) Use of low-emission slurry-spreading technologies (accounting for the saved N in nutrient plans);

(e) Rapid soil incorporation of ammonia-rich organic amendments.

68. Top land-use and landscape management measures to be implemented in practice can be divided into two groups: those related to a geographically targeted land-use change, and those related to geographically adapted management practices at landscape/regional scale.

69. Key land-use change measures identified include:

(a) Set-aside/grassland (with no addition of fertilizers);

(b) Establishment of riparian buffer strips, or of biodiversity buffer strips around or within fields (the difference being the proximity to an aquatic environment;

(c) Hedgerows and afforestation;

(d) Changed crop rotation/perennial crops (for example, permanent grasslands);

(e) Agroforestry;

(f) Wetlands and watercourse restoration and/or constructed mini-wetlands.

70. Key management options for geographically oriented measures at landscape and regional scales include:

(a) Soil tillage and conservation (for example, no tillage of organic soils);

(b) Drainage measures and controlled drainage;

(c) Grassland management;

(d) Placement of livestock production;

(e) Spatial redistribution of manure;

(f) Fertigation and installation of proper irrigation system for dry cultivated areas;

(g) Placement of biogas plants and biorefineries for biomass redistribution.

71. It is recognized that more farmers are adopting practices referred to as "regenerative agriculture", with some practices
<figure><img src="image_108.png" /></figure>

having potential to reduce different N losses, including no-
till, "organic farming" (avoiding manufactured inorganic
fertilizers and focusing on biological nitrogen fixation) and
activities designed to increase carbon sequestration, etc. As
with other agricultural approaches, such systems provide

the opportunity to design bespoke "packages of measures"
to foster sustainable nitrogen management. These require
further assessment to quantify their effects for all forms
of N loss, including emissions of NH₃, N₂O, NOₓ and N₂ and
leaching of NO₃⁻ and other Nₐ forms.
<figure><img src="image_109.png" /></figure>

# Chapter III: Principles of integrated sustainable nitrogen management

Lead author: Oene Oenema

Contributing authors: Wilfried Winiwarter, Shabtai Bittman, Patrick Durand, W. Kevin Hicks, Natalia Kozlova, Sergiy Medinets, Eduard Vasilev and Mark A. Sutton

## A. Introduction and background

72. Nitrogen provides substantial benefits to society, especially by boosting crop productivity. However, nitrogen (N) losses present multifaceted problems affecting human health and the environment. These N-related problems straddle many scientific disciplines, and many domains across policy and regulation. This means that an integrated approach is required to manage N use optimally, avoiding trade-offs and allowing multiple benefits to society and the environment (Oenema and others, 2011b). As agriculture is the one sector where N is introduced intentionally to increase crop yield and quality for financial gain, it is the clearest example of why an integrated approach is required.

73. Nitrogen management in agriculture has a dual purpose: to decrease N losses to protect human health and the environment; and to optimize the beneficial effects of N related to food production. The adjectives "integrated" and "sustainable" in the title refer to the fact that N management needs to be balanced and durable – for example, environmentally sound, socially acceptable and economically profitable – for current and future generations. The negative effects of N losses on human health, ecosystem services, biodiversity, water and climate need to be addressed fully. Integrated sustainable N management contributes to achieving most of the Sustainable Development Goals. Notably, integrated sustainable N management contributes directly or indirectly to achieving Goal 1 (no poverty), Goal 2 (zero hunger), Goal 3 (good health and well-being), Goal 6 (clean water and sanitation), Goal 12 (responsible consumption and production), Goal 13 (climate action), Goal 14 (life below water) and Goal 15 (life on land). At present, the widespread evidence of adverse effects of nitrogen pollution through air, climate, land and water (Galloway and others, 2008; Fowler and others, 2013; Sutton and others, 2011, 2019; Alcamo and others, 2013) demonstrates that further action is needed to improve the effectiveness of N abatement and mitigation measures in agriculture to reduce these effects (European Environment Agency, 2015). Integrated sustainable N management provides a basis for mobilizing more sustained and coordinated action, while taking account of agroecological principles, as a basis for achieving multiple Sustainable Development Goals.

74. The purpose of this chapter is to outline the principles of integrated sustainable N management in agriculture. Section B below considers five important dimensions that

any N management needs to cover to be effective. Section C describes key points of N cycling in the biosphere, to inform the reader about the nature of the N cycle in relation to agricultural practice. Section D discusses principles of nitrogen management in agriculture. Section E then presents some general tools for integrated N management. Possible measures to decrease N losses and to increase N use efficiency in agriculture are presented in subsequent chapters.

## B. Dimensions of integrated sustainable nitrogen management

75. Many countries aspire to develop more integrated and effective approaches to decreasing N losses from agriculture. However, current environmental policies typically have a narrow scope as regards N management. Integration is defined here as the process of combining separate elements and aspects in an organized way, so that the constituent units are linked and function cooperatively. There are five important dimensions of integration in N management, namely:

(a) Cause and effect;

(b) Spatial and temporal integration of all N forms and sources;

(c) Multiple nutrients and pollutants;

(d) Multiple stakeholder types, involvement and integration; and

(e) Regional integration.

These dimensions build on earlier description (Oenema and others, 2011b) and are discussed further below.

### 1. Cause and effect

76. This dimension is a basis of all current N policies, as the human health effects and ecological impacts of the pollution caused by N emissions provide the justification for and underpin the policy measures to decrease such emissions.

77. The "cause and effect" or "source and impact" dimension is also related to the DPSIR framework (see European Environment Agency, 1995). This framework provides insights into cause-effect and economic-environmental relationships, as well as the possible responses of societies and Governments.
<figure><img src="image_110.png" /></figure>

## 2. Spatial and temporal integration of all N forms and sources

78. Spatial and temporal integration in N management relates to combining all N forms, N sources and N emissions within a certain area and timescale in the management plan. Partial forms of this type of integration are contained in the Gothenburg Protocol; for example, most NOₓ and NH₃ sources have been included, but NOₓ emissions from agricultural soils, (semi-) natural NOₓ and NH₃ sources, N₂O emissions to air and N leaching to waters are, as yet, not included when assessing compliance with emission reduction commitments. Similarly, in the European Union Nitrates Directive, all N sources in agriculture have to be considered for reducing NO₃⁻ leaching to waters, but NH₃ and N₂O emissions to air are not addressed explicitly. The European Union Birds Directive<fnref n="8" /> and Habitats Directive<fnref n="9" /> require all N forms, N sources and N emissions to be addressed in so far as they are factors influencing the ecological requirements of protected habitats and species. The emission of gaseous N₂ through denitrification is not directly considered in any of these policies. Although emission of gaseous N₂ does not lead directly to adverse environmental effects, its release can be considered as a waste of the energy used to produce N, as well as a lost resource of useful nitrogen, indicating the need for N₂ emissions to also be addressed. These issues were recently raised in United Nations Environment Assembly resolution 4/14 on sustainable nitrogen management (see UNEP/EA.4/Res.14) and its follow-up in the Colombo Declaration (UNEP, 2019).

79. Conceptually, the N cascade model (Galloway and others, 2003, 2004) is a good example of spatial integration operating over different timescales, but this model has yet to be made operational for management actions. The N cascade is a conceptual model for analysing cause and effect integration, especially when cost-benefit analyses are included.

## 3. Multiple nutrients and pollutants

80. There are two main reasons to integrate N management with that of other specific elements (compounds) in environmental policy, namely:

(a) The other elements (compounds) may cause similar environmental effects; and

(b) Interactions between N species and these other elements and compounds may be large.

81. From a practitioner's point of view, there can be benefits when managing N and other specific elements simultaneously. This holds true, for example, for N and phosphorus (P) in agriculture and sewage waste treatment, and for NOₓ and SO₂ and PM from combustion sources.

82. This type of integration is included partially in the Gothenburg Protocol and the European Union National Emission Ceiling Directive<fnref n="10" />, which address emissions of NOₓ, NH₃ and SO₂ to air, because these emissions contribute to rather similar environmental effects (air pollution, acidification, eutrophication). Similarly, emissions of N and P to surface waters both contribute to eutrophication and biodiversity loss, and thus European Union policies related to combatting eutrophication of surface waters address N and P simultaneously (for example, in the European Union Water Framework Directive<fnref n="11" />). Furthermore, the N and carbon (C) cycles in the biosphere are intimately linked, and perturbations of these cycles contribute to changes in the emissions of the greenhouse gases CO₂, CH₄ and N₂O, which are commonly addressed by climate change policies simultaneously. Nitrogen may also affect CO₂ and CH₄ emissions through its effect on C sequestration in the biosphere and by alteration of atmospheric chemistry (Butterbach-Bahl, Kiese and Liu, 2011a). Due to its multiple effects across all these issues, a focus on nitrogen management can serve to connect the multiple impacts and effects. Linking between the various nitrogen forms (N₂, NH₃, N₂O, NOₓ, NO₃⁻, etc.) serves as a manageable next step in integration. In addition, it provides a framing that demonstrates the multiple linkages between the cycles of N, C, P, sulphur (S), potassium (K), silicon (Si) and many other elements, including micronutrients.

## 4. Multiple stakeholder types, involvement and integration

83. Any N management policy, whether integrated or not, needs to be:

(a) Policy-relevant – for example, address the key issues;

(b) Scientifically and analytically sound;

(c) Cost effective – for example, costs have to be in proportion to the objective to be achieved; and

(d) Fair to users.

84. When one or more of these principles is not respected, the management policy will be less effective, either because of a delay in implementation or through poor implementation and performance, or a combination of those factors. Successful application of the above-mentioned principles requires communication between actors from policy, science and practice. The credibility and relevance of science-policy-practice interactions are, to a large extent, determined by “boundary” work at an early stage in the communication process between policy, science and practice (Tuinstra and others, 2006; Clark and others, 2016). Boundary work is defined here as the practice of maintaining and withdrawing boundaries between science, policy and practice, thereby shaping and reshaping the science-policy-practice interface.

<footnote n="8">8 Directive 2009/147/EC of the European Parliament and of the Council of 30 November 2009 on the conservation of wild birds, *Official Journal of the European Union*, L 20 (2010), pp. 7–25.</footnote>

<footnote n="9">9 Council Directive 92/43/EEC of 21 May 1992 on the conservation of natural habitats and of wild fauna and flora, *Official Journal of the European Communities*, L 206 (1992), pp. 7–50.</footnote>

<footnote n="10">10 Directive (EU) 2016/2284 of the European Parliament and of the Council of 14 December 2016 on the reduction of national emissions of certain atmospheric pollutants, amending Directive 2003/35/EC.</footnote>

<footnote n="11">11 Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy, *Official Journal of the European Communities*, L 327 (2000), pp. 1–72.</footnote>
<figure><img src="image_111.png" /></figure>

85. Communication with stakeholders (for example, fertilizer manufacturers, food producers, processing and retail, society at large) is extremely important. Such stakeholders' views must be integrated as early as possible during the design phase of N management plans and measures, notably for advisors and the practitioners who, in the end, have to implement the management measures. Integration of stakeholders' views may range from public consultation procedures and hearings to participatory approaches and learning. A good example of the latter approach is the European Union Water Framework Directive, which requires full stakeholder involvement for the establishment of river basin management plans.

86. Integration of stakeholders' views does not lead to faster decision-making; on the contrary, the decision-making process often takes more time. Public consultation procedures can be time-consuming, although techniques such as multi-criteria decision-making may support decision-making effectively. This approach aims to find a way out of conflicts and solutions in a transparent process. Integration of stakeholders' views may ultimately improve acceptance of management strategies, and thereby facilitate their implementation in practice.

<figure><img src="image_112.png" /><figcaption>**Image 2:** Fostering stakeholder communication is essential. Here farmers exchange views about low-protein animal feeding in dairy production (photograph: © Wageningen University & Research).</figcaption></figure>

## 5. Regional integration

87. Regional integration or "integration of larger spatial scales" is considered here as the fifth dimension of integration. Regional integration aims at enhanced cooperation between regions and landscapes. It relates to integration of markets and harmonization of governmental policies and institutions between regions through political agreements, covenants and treaties (Bull and others, 2011). Arguments in favour of regional integration include:

(a) Enhancement of markets;

(b) Creation of a "level playing field" for policy measures;

(c) The transboundary nature of environmental pollution;

(d) Consideration of indirect pollution effects; and

(e) The increased effectiveness and efficiency of regional policies and related management measures.

88. In terms of N management, regional integration relates, for example, to the harmonization and standardization of environmental policies across the European Union and for air pollution across the UNECE region (Bull and others, 2011). The river basin or catchment management plans developed within the framework of the European Union Water Framework Directive are also a form of regional integration. Here, water quantity and quality aspects are considered in an integrated way for a well-defined catchment. The European Union Marine Strategy Framework Directive<fnref n="12" /> also promotes integration at the regional level by ensuring consistent determinations of good environmental status and targets under its fifth qualitative descriptor (eutrophication) (see annex I to Marine Strategy Framework Directive) and coordination of programmes of measures, supported by regional sea conventions such as the Helsinki Commission for Baltic Marine Environment Protection (HELCOM) and the Convention for the Protection of the Marine Environment of the North-East Atlantic.

89. The trend towards regional integration during recent decades does not necessarily mean that local management actions are less effective and/or efficient. Local actions can be made site-specific and, as a consequence, are often more effective than generic measures. This holds true for households, farms and businesses, especially when actors can have influence on the choice of actions. In addition, motivation for contributing to the local environment and nature protection can be greater than that for contributing to the improvement of the environment in general.

## C. Key points of nitrogen cycling

90. This section describes the key points of N cycling in the biosphere that underpin the N cycle in relation to agricultural practice. These key points provide the starting point from which to consider the principles of sustainable nitrogen management described further on in this document. "Principles" are understood here as "fundamental truths" and/or "well-established scientific and practical knowledge" that should be familiar to all practitioners, N managers and policymakers. The key points of nitrogen cycling also represent informing principles.

91. Ten key points related to N cycling are distinguished below. These form a "bridge" between this section and the next section, which deals with the principles of integrated N management in agriculture:

<footnote n="12">¹² Directive 2008/56/EC of the European Parliament and of the Council of 17 June 2008 establishing a framework for community action in the field of marine environmental policy, *Official Journal of the European Union*, L 164 (2008), pp. 19–40.</footnote>
<figure><img src="image_113.png" /></figure>

**Key point 1. Nitrogen is essential for life.**

92. Nitrogen forms a key element of chlorophyll in plants, of haem in blood, and of amino acids (protein), nucleic acids and adenosine triphosphate in living organisms (including bacteria, plants, animals and humans). The natural nitrogen cycle is characterized by limited availability of nitrogen forms for living organisms; therefore the natural nitrogen cycle is a nearly closed system, with nitrogen being recycled and reused effectively. Due to this limited availability, nitrogen is often a limiting factor for plant growth. The competition between plant species for the limited amounts of available N (and other growth-limiting elements) is a main factor for biodiversity in natural systems.

93. In agricultural systems, significant crop-yield responses can be obtained when N is added as animal manure or fertilizer, especially when application is balanced with other key nutrients. It has been estimated that around half of the world's population is now alive because of the increased supply of fertilizer N, illustrating the massive impact that N has had in meeting human food needs, thereby allowing the world population to expand rapidly (Erisman and others, 2008; Sutton and others, 2013). Forecasts suggest that more N will be needed during the next few decades if current diets are to be matched with population increases, especially in Africa and parts of Asia (Godfray and others, 2010).

**Key point 2. Excess nitrogen has a range of negative effects, especially on human health, ecosystem services, biodiversity, water and climate change.**

94. The total amounts of N introduced into the global biosphere by human activities have significantly increased during the last century, more than doubling (Galloway and others, 2008), and have now exceeded critical limits for the so-called safe operating space for humanity (Steffen and others, 2015). The deleterious effects of excess N on human health and biodiversity are most apparent in regions with intensive agriculture, especially intensive animal husbandry, urban areas and in large rivers and coastal areas. Nitrogen has both warming and cooling effects on climate (Butterbach-Bahl and others, 2011b), while also contributing to stratospheric ozone depletion (Alcamo and others, 2013). The negative effects of excess N in the environment provide the justification for N emission-abatement policy measures.

**Key point 3. Nitrogen exists in multiple forms.**

95. Nitrogen is transformed from one form to another through biochemical processes, mediated by microorganisms, plants and/or animals, and through chemical processes, mediated by increased temperature and pressure, atmospheric light and possible catalysts (Smil, 2004; Hatfield and Follett, 2008; Schlesinger and Bernhardt, 2013).

96. This has a number of implications: most nitrogen forms are “reactive”, because these forms are easily transformed in the biosphere into another form through biological, photochemical and radiative processes. Reactive nitrogen compounds ($N_r$) include:

(a) Inorganic reduced forms, such as ammonia ($NH_3$) and ammonium ($NH_4^+$), collectively ($NH_x$);

(b) Inorganic oxidized forms, for example, $NO_x$, nitric acid ($HNO_3$), nitrous acid (HONO), nitrous oxide ($N_2O$), nitrite ($NO_2^-$) and nitrate ($NO_3^-$);

(c) Organic reduced forms, such as urea, amines, proteins and nucleic acids.

97. Reduced forms are energy donors, proton donors and electron acceptors; energy is captured from industrial processes and biological nitrogen fixation, meaning that $NH_x$ is an important resource. Oxidized forms are proton acceptors and electron donors. One reduced form, dinitrogen ($N_2$), is not reactive (it is chemically extremely stable), because a lot of energy is needed to break the bonding between the two N atoms;

98. All gaseous and liquid $N_r$ forms are toxic to humans and animals (and plants) when exposure occurs to sufficiently high concentrations. The toxic concentration levels greatly differ between forms and among organisms. **Nitrogen is "double mobile"**, because some forms are easily transported via air and water:

(a) Nitrogen is transported in the air as gases, such as dinitrogen ($N_2$), nitrous oxide ($N_2O$), $NO_x$ (including NO and $NO_2$), nitric acid ($HNO_3$), nitrous acid (HONO) and ammonia ($NH_3$), amines and other volatile organic nitrogen (VON) and as aerosols, including fine PM formed from among other things, nitrate ($NO_3^-$), ammonium ($NH_4^+$) and particulate organic nitrogen (PON);

(b) Nitrogen is transported dissolved in water as nitrate ($NO_3^-$), ammonium ($NH_4^+$), urea ($CO(NH_2)_2$), dissolved organic nitrogen (DON) and nitrous oxide ($N_2O$), and is transported suspended in water as particulate organic nitrogen (PON).

**Key point 4. The same atom of N can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on human health.**

99. This phenomenon is called the “nitrogen cascade”, which has been defined as the sequential transfer of $N_r$ through environmental systems and which results in environmental changes as $N_r$ moves through or is temporarily stored within each system (Galloway and others, 2003).

**Key point 5. Nitrogen moves from soil to plants and animals, to air and water bodies, and back again, and from one region to another, as a result of natural drivers and human activities, which have to be understood for effective N management.**

100. The natural drivers are:

(a) Solar radiation, which drives photosynthesis, the hydrological cycle, wind and temperature differences, and mass flow in air and water;

(b) Gravitation, which drives the earth movement and erosion;

(c) Earth tectonics, which drives earthquakes and volcanisms;

(d) Lightning and biological nitrogen fixation, which form reactive N;

(e) Turbulent diffusion, molecular diffusion and Brownian motion, which drive gas and particulate dispersion.
<figure><img src="image_114.png" /></figure>

101. The cycling rate and residence times in air, water and soil differ greatly between N forms. In the atmosphere, gases such as NH₃, NOₓ, and HONO have a short residence time in air (days, weeks), while N₂O remains in the atmosphere for more than a century and N₂ even longer. Residence times are related to the reactivity of the N forms. In water systems, nitrogen residence times may range from years to many centuries depending on the nature of the aquifer and groundwater storage.

**Key point 6. Human activities have greatly altered the natural N cycle and have made the N cycle more leaky.**

102. Land-use change, urbanization, the creation of inorganic N fertilizer, and the globalization of food systems are among the most fundamental changes created by human activities (Vitousek and others, 1997; Fowler and others, 2013). Urbanization and the globalization of food systems have resulted in increased transport of food and feed produced in rural areas (where nitrogen depletion occurs) and to areas where food and feed are being utilized, especially in urban areas and in areas with livestock (where regional nitrogen enrichment occurs). The regional spatial segregation of food and feed production and consumption is also one of the key factors why N use efficiency at whole food system level has decreased in the world during the last decades (Lassaletta and others, 2014; Oita and others, 2016).

**Key point 7. The nature and human alterations of the N cycle challenge the realization of both a circular economy and integrated sustainable N management; policymakers and decision makers from both areas may learn from each other.**

103. Many principles of the “circular economy” and “circular systems” also apply to the principles of integrated sustainable N management, including the principles of:

(a) Reduction of losses;

(b) Reduction, reuse and recycling of wastes;

(c) Realignment and reduction of inputs;

(d) Reconsideration of protein consumption levels (for example, minimization of excess); and

(e) Changing systems to make them less leaky and more resilient.

104. The concept of the “nitrogen circular economy” (Sutton and others, 2019), and circularity more generally, originate from industrial ecology (Jurgilevich and others, 2016), which aims to reduce resource consumption and emissions to the environment by closing the loop of materials and substances, including N and other nutrients. Increasing circularity in food production requires a rethink of economic growth, human diets, agricultural policy and regulations related to fertilizers and food waste (De Boer and van Ittersum, 2018).

**Key point 8. Most of the nitrogen in plants is taken from soil via roots in the form of nitrate (NO₃⁻) or ammonium (NH₄⁺), indicating that the NO₃⁻ and NH₄⁺ need to be in the vicinity of plant roots and available at the right time to be effective for plant growth.**

105. The N uptake depends on the N demand by the

crop, the root length density and distribution and the concentrations of NO₃⁻ and NH₄⁺ in the soil solution. The N demand by the crop depends on crop type and variety and climate. The uptake rate of N in plants commonly follows Michaelis–Menten kinetics. This implies that a maximum rate is achieved at a saturating substrate (NO₃⁻, NH₄⁺) concentration, so that surplus N is not used and at risk of being wasted as pollution (following the law of diminishing returns). Both the demand for N of the crop and the supply of N via the soil are influenced by soil and weather conditions and management. Dominant sources of NO₃⁻ and NH₄⁺ in soil are (Marschner, 2012):

(a) Mineralization of organically bound nitrogen in soil;

(b) Inputs via atmospheric deposition;

(c) Inputs via animal manure, compost and wastes;

(d) Inputs via inorganic N fertilizers.

106. However, some N (for example, gaseous NH₃ and NO₂ from ambient atmospheric deposition) may be taken up directly by plant leaves (Sutton and others, 1995; Sparks, 2009). In unfertilized agroecosystems, forests and natural habitats, mycorrhizae (soil fungi living in association with plants) can play an important role in bringing nutrients to plant roots. High levels of external nitrogen input can affect the performance of such mycorrhizal symbioses.

**Key point 9. Some crop types are able to convert non-reactive dinitrogen (N₂) from air into reactive N forms (amine, protein) in the plant roots through association with specialist blue green bacteria. This biological N fixation is an important source of reactive N in the biosphere, including agriculture.**

107. Important crops include the legume family (Fabaceae or Leguminosae) with taxa such as (soy)beans, peas, alfalfa, clover and lupins. They contain symbiotic bacteria, especially rhizobia, within nodules in their root systems, which are able to convert N₂ into NH₃ from which amines are produced (Herridge and others, 2008). The N₂ fixation rate depends on the availability of NO₃⁻ and NH₄⁺ in soil; the fixation rate is suppressed when the availability of NO₃⁻ and NH₄⁺ in soil is high, and vice versa. The fixation rate also depends on the availability of substantial chemical energy (carbohydrates) and other essential nutrient elements, including phosphorus, calcium and molybdenum. Non-symbiotic N₂ fixation by free-living soil microorganisms can represent an additional input of reactive N to the ecosystems (Ladha and others, 2016).

**Key point 10. Humans and animals require protein-N and amino acids for growth, development and functioning, but only a minor fraction of the N is retained in the growing body weight and/or milk and egg.**

108. The remainder is excreted, mainly via urine and faeces, and this N can be recycled and reused. The protein N need (or amino acid requirements) of animals mainly depends on animal category, body weight, growth rate, milk and egg production, activity (labour, grazing) and reproduction (McDonald and others, 2010; Suttle, 2010). The N retention in animal production is strongly dependent on animal breed,
<figure><img src="image_115.png" /></figure>

feed quality, age and herd management, and commonly ranges from 5 to 15 per cent in beef production, 15 to 30 per cent in dairy production, 25 to 40 per cent in pork production and 40 to 50 per cent in poultry production (Gerber and others, 2014). The remainder is excreted as urea in urine (uric acid in poultry) and in animal manure. Typically, half of N excretion is in the form of urea (and ammonium (NH<sub>4</sub>⁺)) and half in organically bound form, depending on the protein content of the feed. Animal manure and urine provide a valuable source of nutrient elements and organic C in natural and agricultural systems. However, animal manures and urine are also main sources of ammonia (NH<sub>3</sub>) and nitrous oxide (N<sub>2</sub>O) emissions to air, and of N leaching to groundwater and surface waters, depending on management and environmental conditions.

## D. Principles of integrated sustainable nitrogen management in agriculture

109. Twenty-four principles of integrated sustainable nitrogen management are identified:

**Principle 1: The purpose of integrated sustainable nitrogen management in agriculture is to decrease nitrogen losses to the environment to protect human health, climate and ecosystems, while ensuring sufficient food production and nitrogen use efficiency, including through appropriately balanced nitrogen inputs.**

110. As the key input, along with water, the importance of N for food security cannot be overstated. The effectiveness of integrated sustainable N management in agriculture can be assessed through applying consistent metrics (see box III.1).

**Principle 2: There are various actors in agriculture and the food chain, and all have a role and responsibility in N management.**

111. These actors include:

(a) Suppliers of fertilizers, feed, germplasm, seed, machinery and loans;

(b) Advisors, extension services, accountancy specialists and financial organizations;

(c) Farmers;

(d) Product handling and processing industries (crop products, dairy, meat, manure);

(e) Retail organizations;

(f) Consumers;

(g) Governments and NGOs, including food testing; and

(h) Scientists.

112. Evidently, farmers have a direct role to play in N management, in enhancing N use efficiency and in minimizing N losses to the environment. Therefore, farmers reap the economic benefits and bear the burdens of the measures needed to decrease N losses. Incorporation of certain N measures offers net economic benefits that can contribute to farm business planning and circular economy development. For other measures, the costs of implementation exceed the

agricultural benefits arising from the greater retention of N in the agricultural system, and may only be justifiable from an environment, health and climate perspective. The net costs are as yet difficult to transfer to (spread over) other actors in the food production – consumption chain, because farmers have little or no “market power” in a globalized food system. Farmers may be reluctant to implement costly measures to reduce N losses because they want to maximize income and fear losing competitiveness relative to farmers who do not implement measures. Providing access to funding/ financing via appropriate instruments may therefore need to be considered as part of the policy to support the transition to more integrated sustainable nitrogen management. **There is thus a joint responsibility for all actors in the food chain, including for policymakers at several levels, to support a decrease of N losses and to share the cost and benefits of N abatement/mitigation measures. This should be done in concert with other critical policies, including mitigating climate change.**

**Principle 3: Specific measures are required to decrease pathway-specific N losses.**

113. The dominant N loss pathways in agriculture are:

(a) NH<sub>3</sub> volatilization;

(b) Downward leaching of (mainly) nitrate to groundwater and then to surface waters;

(c) Overland flow and erosion of basically all N forms to surface waters; and

(d) Nitrification-denitrification processes combined with the gaseous emissions of NO<sub>x</sub>, N<sub>2</sub>O and N<sub>2</sub>.

114. These pathways are influenced by a complex of controlling factors, including the availability and form of N sources, climate, soil and geomorphological/hydrological conditions and management. **Pathway-specific measures have to consider pathway-specific controlling factors** (Hatfield and Follett, 2008; Bittman and others, 2014; UNECE, 2013).

**Principle 4: Possible trade-offs in the effects of N loss abatement measures may require priorities to be set, for example, which adverse effects should be addressed first.**

115. In practice, the outcome will depend on a quantification – a small negative effect of one kind may be tolerated when there is a huge improvement elsewhere – and on policy guidance on how to compare the importance of issues (for example, N eutrophication versus greenhouse gas emissions through N<sub>2</sub>O emissions versus human health effects through NH<sub>3</sub> emissions and associated formation of small particles PM<sub>2.5</sub> (Sutton and others, 2011)). There may also be non-N agricultural trade-offs, and even non-agricultural trade-offs. Policy guidance is necessary to inform such priorities and properly weigh the options according to local to global context and impacts.

**Principle 5: Nitrogen input control measures influence all N loss pathways.**

116. These are attractive measures to decrease N losses in an integrated manner, because reductions in nitrogen input (for example, by avoidance of excess fertilizer, of excess
**Box III.1: Metrics for assessing the effectiveness of integrated sustainable nitrogen management.**

One of the core purposes of integrated sustainable nitrogen management in agriculture is to decrease N losses to the environment to protect human health, ecosystems, climate and other aspects of economy and sustainability, while ensuring adequate crop and animal production (principle 1).

Indicators to reflect this principle have been proposed by the European Union Nitrogen Expert Panel (Oenema and others, 2015), with a focus on Nitrogen Use Efficiency (NUE):

NUE = Sum of N outputs / Sum of N inputs .................................................... (percentage, per cent)

N surplus = Sum of N inputs – Sum of N outputs .................................................... (kg N /ha /yr)

N in harvested or other utilized outputs .................................................................... (kg N /ha /yr)

Evidently, a high NUE indicates that N input is being used efficiently. A low N surplus indicates that the potential for N loss and impacts on the environment is low, with a large part of the N input recovered in N in harvested products. The approach is relevant from multiple perspectives, for crops, livestock, agrifood system and across the economy (Bleeker and others, 2013; Sutton and others, 2013; Westhoek and others, 2015; Erisman and others, 2018).

The effects of measures aimed at the abatement of specific nitrogen loss pathways are commonly expressed in terms of abatement efficiency (AE), reduction in N loss and overall change in NUE:

AE = (Unabated N loss – Abated N loss) / Unabated N loss .................................................... (percentage, per cent)

Total reduction in N loss .................................................................................................... (kg N /ha /yr)

Change NUE = (NUE revised – NUE reference) / NUE reference .................................................... (percentage, per cent)

Another approach focused on reducing overall environmental impact considers global and national reduction in total “nitrogen waste”, this being the sum of all nitrogen losses to the environment (including N₂ and all N, forms). This approach is reflected in the ambition of the Colombo Declaration (UNEP, 2019; Sutton and others, 2019) to “halve nitrogen waste” from all sources, as a contribution to achieving the United Nations Sustainable Development Goals:

$$ \text{Reduction in total N waste} = \frac{(\text{Reference N waste-Revised N waste})}{(\text{Reference N waste})} \text{.................................................... (percentage, per cent)} $$

Whereas AE focuses on the performance of specific measures on each form of N loss, the reduction in total N waste emphasizes the benefit of all reductions in N losses, by all approaches at national, regional and global scales. Further work is needed to agree international protocols for each of these indicators to assist countries in preparing data sets and to enable informed comparison of different indicator values and target values.

protein in animal diets, and of any human foods with high nitrogen footprint) lead to less nitrogen flow throughout the soil-feed-food system, reducing losses of all forms of nitrogen pollution. For example, Westhoek and others (2015) showed that halving meat and dairy intake by European citizens (which is currently in excess of health needs) would reduce nitrogen pollution by 40 per cent (for NH₃) and by 25–40 per cent (for N₂O and NO₃⁻ leaching) in the absence of any technical measures. The reason for the range for N₂O and NO₃⁻ is that substantial agricultural land would also be liberated for other purposes, allowing alternatives such as increased crop production for export (net 25 per cent abatement) or “greening measures”, which deliver the maximum reduction in nitrogen pollution (net 40 per cent abatement). Further assessments are needed to consider the impact of consuming unessential, non-livestock-based foods and beverages.

**Principle 6: A measure to reduce one form of pollution leaves more N available in the farming system, so that**

**more is available to meet crop and animal needs.**

117. This means that reducing one form of N loss involves the risk of increasing other forms of N losses, sometimes termed “pollution swapping”, unless inputs and outputs (including N storage in soils) are changed. In order to realize the benefit of a measure to reduce N losses (and to avoid pollution swapping), the nitrogen saved by the measure needs to be matched by either reduced N inputs or increased N in harvested outputs (including N storage in soil). Reduced N inputs or increased harvested outputs are thus an essential part of integrated nitrogen management, while providing opportunity for increased economic performance (Oenema and others, 2009; Quemada and others, 2020).

**Principle 7: The N input-output balance encapsulates the principle that “what goes in must come out”, making it a key indicator of N management.**

118. Based on the law of mass conservation, inputs must match outputs or be temporarily stored within the farm
<figure><img src="image_116.png" /><figcaption>**Figure III.1:** Concept of the nitrogen input – output mass balance of mixed crop – livestock production systems</figcaption></figure>

<figure><img src="image_117.png" /></figure>

*Source:* Modified from Oenema and others (2009).

*Note:* The “hole-in-the-pipe” model (after Firestone and Davidson, 1989) illustrates the “leaky N cycle” of crop and animal production; it shows the fate of N inputs in agriculture. Inputs and outputs in useful products and emissions to air and water show dependency in crop production and animal production; a change in the flow rate of one N flow has consequences for others, depending also on the storage capacity of the system. Total inputs must balance total outputs, following corrections for possible changes in storage within the system. The concept is applicable at field, farm, regional and global scales for all types of farms (Oenema and others, 2009

system. Hence, N input = N output in harvested products (+ temporal N storage) – N losses (see figure III.1). It illustrates also that N input control is a main mechanism to reduce N losses. It also allows for strategies based on maximization of N in storage pools, including in manure, soil and plants (for example, by promoting plant uptake of N). Internationally agreed protocols are needed for making these N input-output balances; N inputs and N outputs must be recorded in a uniform manner to allow fair comparisons between farms and regions, and to circumvent bias.

**Principle 8: Matching nitrogen inputs to crop-needs (also termed “balanced fertilization”) and matching protein N inputs to livestock needs offers opportunities to reduce all forms of nitrogen losses simultaneously that can help to improve economic performance at the same time.**

119. Hence, increasing “partial factor productivity” (defined as harvest output per unit of N input) increases N use efficiency and reduces all forms of N losses. This follows directly from the above-mentioned law of mass conservation. Furthermore, the law of diminishing returns must be considered when matching N inputs to crop needs; with increasing N input, crop yield and N uptake increase only marginally, while N losses tend to increase progressively. These basic principles equally hold true for crop and animal production and overall food production.

**Principle 9: Spatial variations in the vulnerability of agricultural land to N losses require spatially explicit N management measures in a field and/or landscape**

(including with the aid of precision farming techniques and tools).

120. The surface of land is often sloping and soils are often heterogeneous in nature, while the weather is variable and uncertain, which indicates that crop growth conditions, soil N delivery and N loss pathways are variable in space and time. Such spatially diverse conditions can only be addressed by locally fine tuning agricultural management techniques (such as “precision farming” techniques, where management actions are adjusted for each field location) and use of site-specific emission-abatement measures. This principle is applicable to field application of both organic and inorganic fertilizer resources (see chapter V).

**Principle 10: Spatial variations in the sensitivity of natural habitats to N loadings originating from agriculture highlight the need for site- and region-specific N management measures.**

121. A source-pathway-receptor approach may help to target specific hot spots, specific N loss pathways and specific sensitive areas. This holds true especially for natural habitats that are sensitive to N loading in an agricultural landscape with intensive livestock farms; the latter are likely hot spots for NH₃ emissions, while the natural habitats are likely highly sensitive to N inputs via atmospheric deposition. The same principle applies to drinking water reservoirs, pristine lakes, streams and coastal waters; these need special protection to prevent pollution. This principle underlies added benefits from landscape-level N management (see chapter VI).