spite of a high growth of weeds, MW treatment showed better banana growth than PW and did not suffer from any reduction of banana growth in comparison to CT.

<table><caption>Table 1. Response of the banana pseudostem girth to experimental treatments</caption><thead><tr><th rowspan="2">Experimental treatment</th><th colspan="2">48 DAP</th><th colspan="2">100 DAP</th><th colspan="2">160 DAP</th></tr><tr><th>C30</th><th>FE</th><th>C30</th><th>FE</th><th>C30</th><th>FE</th></tr></thead><tbody><tr><td>MW: Mulch + weed cover</td><td>11.9 A</td><td>5.5</td><td>27.0 A</td><td>15.23 A</td><td>60.9 A</td><td>26.01 A</td></tr><tr><td>CT: Ploughing + chemical weed control</td><td>10.8 AB</td><td>5.5</td><td>24.1 AB</td><td>14.41 AB</td><td>56.8 A</td><td>25.97 A</td></tr><tr><td>PW: Ploughing + weed cover</td><td>9.4 B</td><td>6.1</td><td>22.30 B</td><td>13.96 B</td><td>49.13 B</td><td>24.25 B</td></tr></tbody></table>

## Evolution of the total nitrogen uptake by plants component and the soil mineral nitrogen content

By comparing the estimated nitrogen uptake of the weeds and of the banana plants (cf. figure 1) in control treatments (CT) with PW, we observed that the high amount of nitrogen uptake by weed cover induced a reduction of other N compartment distributed among the N banana uptake and N mineral soil content. However, on MW, instead of weak depletion of mineral N of the soil, there was an increase the global N content of the agrosystem.

<figure><img src="image_173.png" /><figcaption>Figure 1. Dynamic of the repartition of N uptake between weeds banana crop and soil mineral nitrogen.</figcaption></figure>

## CONCLUSION

PW management had an impact by competing with banana growth, that needs to be compensated for by an increase of Nitrogen fertilization. As MW management has no negative impact on the banana growth this management would not require an increase of nitrogen fertilization, its higher nitrogen amount in comparison to conventional management indicated lower nitrogen leaching until this crop stage.

## REFERENCES

* Achard R., 2016. Etude du fonctionnement d'associations entre le bananier et une couverture vivante ; évaluation des potentialités et stratégies d'utilisation de plantes de service pour contrôler les adventices. Thèse de doctorat, Université Paris-Saclay, pp. 187.

* Ripoche A., Achard R., Laurens A., Tixier P., 2012. Modeling spatial partitioning of light and nitrogen resources in banana cover-cropping systems. Eur. Journ. Agr. Vol 41, 81-91.

* Thieuleux, L., 2006. Biodisponibilité de l'azote en cultures bananières sur nitisol. Ph.D. Thesis. Université des Antilles et de la Guyane, Guadeloupe, France, pp. 105.
LANDSCAPE AND NATIONAL LEVEL SOLUTIONS FOR A MORE SUSTAINABLE N MANAGEMENT IN DENMARK

DALGAARD, T.¹, BROCK, S.², CORDOVIL, C.M.S., GRAVERSGAARD, M.¹, HANSEN, B.³, HASHEMI, F.¹, HASLER, B.⁴, HUTCHINGS, N.J.¹, JACOBSEN, B.⁵, JENSEN, L.S.⁶, KJELDSEN, C.¹, OLESEN J.E.¹, SCHJØRRING, J.K.⁶, SIGSGAARD, T.⁷, STUBKJÆR ANDERSEN, P.⁸, TERMANSEN, M.⁵, VEJRE, H.⁸, VESTERGAARD ODGAARD, M.¹, WIBORG, I.A.⁹

¹ Department of Agroecology, Aarhus University, Blichers Allé 20, DK-8830 Tjele, Denmark. tommy.dalgaard@agro.au.dk; ² Aarhus University, Dept. of Culture and Society. Jens Chr. Skous Vej 7, DK-8000 Aarhus C, Denmark; ³ Geological Survey of Denmark & Greenland - GEUS. C.F. Møllers Allé 8, DK-8000 Aarhus C, Denmark; ⁴ Aarhus University, Dept. of Environmental Sciences, Frederiksborgvej 399, DK-4000 Roskilde, Denmark; ⁵ University of Copenhagen, Dept. of Food and Resource Economics. Rolighedsvej 25, DK-1870 Frederiksberg C, Denmark, ⁶ University of Copenhagen, Dept. of Plant and Environmental Sciences. Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark; ⁷ Aarhus University, Dept. of Public Health, Bartholin Allé 2, 8000 Aarhus C, Denmark; ⁸ University of Copenhagen, Dept. Geosciences and Natural Resource Management. Rolighedsvej 23, DK-1858 Frb. C, Denmark; ⁹ SEGES, Knowledge Centre for Agriculture. Agro Food Park 20, DK-8200 Aarhus N, Denmark.

INTRODUCTION

In 2016, The Danish Government introduced an N-policy paradigm shift with a new regulation tailored to local reduction targets rather than the general, national reduction goals applied in previous action plans. It is a large challenge to implement this and has been a turning point for studies in the DNMARK Research Alliance (www.dNmark.org) and the related NitroPortugal coordination and support action, presented in this paper. For instance, a new scheme with watershed advisors (“oplandskonsulenter”) has been implemented, inspired by the DNMARK pilot landscape study sites, and the geographically tailored N regulation will be implemented stepwise over the coming years, with significantly increased implementation of measures like wetlands, mini-wetlands, afforestation and other landscape level filters to prevent reactive nitrogen (Nr) from reaching vulnerable recipients. These measures are integrated on top of the existing general regulation, and assessment of the integrated effect is important both at the landscape scale and at the national scale, and is the turning point for solution scenario development at both landscape and national scales.

MATERIAL AND METHODS

Three different groups of solution (mitigation) scenarios have been explored in the DNMARK alliance: 1) New production chains with more efficient use and recycling of N, 2) Geographically differentiated N-mitigation measures based on planning and management of agricultural landscapes, and 3) Changed consumption patterns driving land use change and reducing N use. The solution scenarios, based on emission factor modelling in line with Hutchings et al. (2014), are evaluated in terms of how they can contribute to and ideally comply with targets agreed for N pollution to surface and groundwater (Water Framework Directive; Nitrates Directive), ammonia volatilization (CAFE) and nitrous oxide (EU climate targets). In addition, the scenarios may depend on their internal logic and the measures adopted can lead to other benefits in terms of effects on biodiversity, nature and ecosystems as well as different types of revenue-generating production.

RESULTS AND DISCUSSION

In this paper, we present the following selected examples of the above scenario categories:

New production chains with more efficient use and recycling of N

* Anaerobic digestion (biogas) of livestock manure (with maize and grass silage added). This results in enhanced N use efficiency of applied manure thereby yielding a lower N leaching and lower N₂O emissions. However, this may increase ammonia volatilization. Overall, this reduces the need for use of mineral N.

* Acidification of livestock slurry in animal housing for respectively cattle and all livestock. This will substantially reduce ammonia volatilization, which enhances the content of mineral N in the manure
applied in the field. This may reduce the need for use of mineral N fertilizer. This will not in itself reduce N leaching, but if combined with use of nitrification inhibitors, in some cropping systems and soil types, there may be a possibility to reduce N leaching during spring time (in particular for N applied to silage maize and potatoes).

<table><caption>Table 1. Examples on results from the national solution scenarios on new production chains with a more efficient use and recycling (Anaerobic digestion (biogas) of livestock manure, and acidification of livestock slurry).</caption><thead><tr><th rowspan="2"></th><th colspan="3">Emissions reductions (% change)</th><th colspan="3">Applied N in field (% change)</th></tr><tr><th>NO<sub>3</sub></th><th>NH<sub>3</sub></th><th>N<sub>2</sub>O</th><th>Fertilizer</th><th>Manure</th><th>Total</th></tr></thead><tbody><tr><th>Biogas</th><td>-11.4</td><td>7.3</td><td>-12.6</td><td>-21.0</td><td>12.4</td><td>1.3</td></tr><tr><th>Acidification (cattle)</th><td>0.3</td><td>-18.3</td><td>-0.7</td><td>-4.7</td><td>2.0</td><td>-0.2</td></tr><tr><th>Acidification (all)</th><td>0.6</td><td>-49.1</td><td>-0.4</td><td>-18.9</td><td>8.9</td><td>-0.3</td></tr></tbody></table>

## Geographically differentiated N-measures based on planning and management of agricultural landscapes

The focus of geographically differentiated N mitigation measures relate to the different susceptibilities of aquatic ecosystems (groundwater, fresh water and marine systems) to N loading across the landscape and to differences in the capacity of landscape components to reduce nitrate to N₂ (groundwater and surface water). The possibilities of applying differentiated N-measures depend highly on the scale at which these are applied, since both vulnerability and N reduction varies greatly across the landscape. In this study the focus was on applying measures (set-aside) for reducing N loadings to the marine environment in Denmark. The N-loading was calculated from the N leaching from the root zone corrected for N reducing in groundwater and surface waters. The effect was assessed by evaluating the area needed to comply with the Water Framework Directive targets for maximum load to individual marine environments. Three different criteria for targeting the placement of set-aside were evaluated: N reduction in groundwater and surface waters, naturalness (biodiversity) of the landscape, and land value.

## Changed consumption patterns driving land use change and reducing N use

Changes in both local and global consumption (and production) patterns will affect N use and N losses in Danish agriculture. For this, we considered two alternative food demand scenarios, which are likely to have an impact on agricultural production, land use and nitrogen balances in Denmark: 1) A changed global consumption scenario, and 2) A local consumption scenario. The first scenario represents a change in the export demand for Danish agricultural products (including the extent to which production to the domestic market will have to adapt to a changed export demand). In contrast, the second scenario represents a change in the domestic food demand behavior and the resulting changes in exports that may follow from this change, given the total area available for agricultural production.

**Acknowledgements:** To Innovation Fund Denmark for support to the www.dNmark.org Research Alliance, and to the EU Commission for support to the NitroPortugal H2020 Twinn-2015 Coordination and Support Action.

## REFERENCE

* Dalgaard T, Hansen B, Hasler B *et al.*, 2014. Policies for agricultural nitrogen management - trends, challenges and prospects for improved efficiency in Denmark. Environ. Res. Lett. 9, 115002.

* Hutchings N, Nielsen O, Dalgaard T *et al.*, 2014. A nitrogen budget for Denmark; developments between 1990 and 2010, and prospects for the future. Environ. Res. Lett. 9, 115012.
# CONTROLLED TRAFFIC FARMING INCREASES ROOT GROWTH, CROP AND SOIL NITROGEN IN VEGETABLE CROPPING SYSTEMS

HEFNER, M.<fnref n="1" />, LABOURIAU, R.², NØRREMARK, M.³, KRISTENSEN, H.L.<fnref n="1" />

## INTRODUCTION

Problems of machinery induced soil compaction are evident in crop production, resulting in changes of nitrogen (N) availability, restricted root growth and reduced yields (Batey & McKenzie, 2006). Controlled traffic farming (CTF) uses GPS signals to keep machine traffic in permanent lanes, which restricts soil compaction to wheel tracks. In our study we compared effects of CTF to random traffic farming (RTF) on root growth, soil N mineralization, N uptake and crop yield, in organic vegetable cropping systems across two soil types in Denmark after a period of two years since establishment. Our hypotheses were that CTF will in contrast to RTF (1) improve root growth, (2) not affect N mineralization and (3) increase crop yield and N uptake.

## MATERIAL AND METHODS

Field experiments were conducted at two commercial organic farms in Denmark from 2013 to 2016. The farm of Skiftekær Økologi (54°58′N, 10°32′E) was situated on a fine sandy loam and the farm of Vostrup Øko (55°89′N, 8°45′E) on a coarse sandy soil. CTF was compared to RTF as the control (n=3). CTF was carried out with auto-guidance and highly accurate RTK-GPS (Real Time Kinematic). Machinery traffic in the CTF plots was restricted to permanent tracks contrary to machinery traffic in the RTF plots. Crop samples were analysed for marketable yields, total biomass and N content to calculate N accumulation; and soil mineral N. Potential soil N mineralization was studied by incubating top soil samples at 25°C for 35 days. Root growth was registered by filming by use of minirhizotrons reaching 1.5 or 2.5 m depth (Xie & Kristensen, 2017). The number of roots was calculated as root intensity and tested by fitting to a Poisson distribution including a random component and adding an offset to improve the statistical analysis. This resulted in an arbitrary (no) unit.

The 5-year crop rotation at Skiftekær Økologi was red clover – white cabbage – potato followed by vetch as a winter cover crop – beetroot – winter squash. The experimental design included the full crop rotation in adjacent fields each year. Three out fields per treatment were sampled each year, being at the same GPS position within the bed throughout the experiment. At Vostrup Øko the 4-year crop rotation was grass-clover – carrot – potato – beetroot with a similar design as at Skiftekær, but only growing one crop each year.

## RESULTS AND DISCUSSION

Crops had more roots at harvest especially in the deep part of the root zone in four out of the six crop seasons at Skiftekær Økologi, that is, in white cabbage and potato in 2015 and in beetroot and winter squash in 2016 (Figure 1). At Vostrup Øko more roots were found under beetroot in 2015 (data not shown). N accumulation was higher in CTF treatments in white cabbage and potato in 2015, but not in beetroot in 2015 or in 2016 at Skiftekær Økologi. The difference was not significant at Vostrup Øko (Table 1). Yields at the two farms followed the same pattern as the N accumulation (data not shown). Soil mineral N was higher below CTF for some crops, whereas potential mineralization of N did not differ between CTF and RTF treatments (data not shown). These results indicate a positive effect of CTF on crop yields, root growth and N accumulation already 2 and 3 years after conversion from RTF at Skiftekær Økologi on a fine sandy loam. However, the effect was not evident every year or clearly linked to crop species. At Vostrup Øko on coarse sandy soil, the effect of CTF was significant only on root growth.

<footnote n="1">¹ Department of Food Science, Aarhus University, Denmark; ² Department of Mathematics, Aarhus University, Denmark; ³ Department of Engineering, Aarhus University, Denmark</footnote>
<figure><img src="image_174.png" /><figcaption>Figure 1. Root intensity at Skiftekær Økologi in 0 to 2 m depth at crop harvest in the sampled fields in 2015 and 2016. Bars show 95% confidence intervals. * indicate significant difference between treatments at p<0.05.</figcaption></figure>

<table><caption>Table 1. Nitrogen accumulation (kg ha⁻¹) in the aboveground plant parts at Skiftekær Økologi (Fields 1-3) and Vostrup Øko. Confidence intervals at 95% are shown. Different letters indicate difference between treatments at p<0.05.</caption><thead><tr><th>Treatment</th><th>Field 1</th><th>Field 2</th><th>Field 3</th><th>Vostrup</th></tr></thead><tbody><tr><td><strong>2015</strong></td><td>White cabbage</td><td>Potato</td><td>Beetroot</td><td>Beetroot</td></tr><tr><td>CTF</td><td>142 (131-153) <sup>a</sup></td><td>153 (134-172) <sup>a</sup></td><td>87 (74-101) <sup>a</sup></td><td>113 (87-139) <sup>a</sup></td></tr><tr><td>RTF</td><td>116 (105-127) <sup>b</sup></td><td>92 (73-111) <sup>b</sup></td><td>71 (57-84) <sup>a</sup></td><td>87 (61-113) <sup>a</sup></td></tr><tr><td><strong>2016</strong></td><td>Potato</td><td>Beetroot</td><td>Winter squash</td><td>-</td></tr><tr><td>CTF</td><td>51 (33-69) <sup>a</sup></td><td>72 (54-91) <sup>a</sup></td><td>68 (50-87) <sup>a</sup></td><td>-</td></tr><tr><td>RTF</td><td>52 (34-70) <sup>a</sup></td><td>68 (49-86) <sup>a</sup></td><td>48 (30-66) <sup>a</sup></td><td>-</td></tr></tbody></table>

## CONCLUSION

CTF increased root growth, yields and N accumulation in several vegetable crops in an organic crop rotation on sandy loam and increased root growth on sandy soil. The results underline the potential of CTF to improve yields and N use efficiency in organic vegetable production.

**Acknowledgements:** The project was funded by the Green Growth and Development programme (GUDP) under the Danish Ministry of Environment and Food and participants in the project ORGANICS IN THE TRAIL.

## REFERENCES

* Batey T., McKenzie D.C. 2006. Soil compaction: identification directly in the field. Soil Use and Management 22, 123-131.

* Xie Y., Kristensen H.L. 2017. Intercropping leek (Allium porrum) with dyer's woad (Isatis tinctoria) increases rooted zone and agro-ecosystem retention of nitrogen. European Journal of Agronomy 82, 21-32.
# EVALUATING THE POTENTIAL OF DIETARY CRUDE PROTEIN MANIPULATION IN REDUCING AMMONIA EMISSIONS FROM CATTLE AND PIG MANURE

AMON, B.<fnref n="1" />, E.P.M, SAJEEV.², ZOLLITSCH, W.³, AMMON, C.<fnref n="1" />, WINIWARTER, W. ⁴,⁵

## INTRODUCTION

Manure management is a prominent source of NH₃ emissions within the livestock sector (UNECE 2016). Various studies have described and quantified the potential of abatement options to reduce NH₃ emissions from manure management (Bittman et al. 2014). The manipulation of CP in animal diets is one such abatement technique to reduce NH₃ emissions from manure management. The reduction of CP in animal diets has been described and recommended as one of the most cost effective and strategic ways to reduce NH₃ emissions from manure management in Annex IX to the Gothenburg protocol (UNECE 2015), as well as in the recent guidance document on NH₃ abatement (Oenema et al. 2014).

NH₃ emission reductions from dietary manipulation of animal diets have been quantified using measured and reported NH₃ emissions from experimental studies (Hou et al. 2015; Oenema et al. 2014). However, there exists considerable variability in the reported emission reduction estimates. This is mainly because these studies do not distinguish between animal types and also discounts for the underlying factors that affect emissions of NH₃ from reduced CP in animal diets. This highlights the need to better quantify the influence of reduced CP on NH₃ emissions, while distinguishing for animal types and also accounting for a range of factors which may influence NH₃ emissions.

This paper aims to address this research gap by presenting a comprehensive analysis of NH₃ emission reductions from lowering CP content in animal diets. The results discussed here examine the relationship between reduced CP and NH₃ emissions distinguishing between cattle and pigs. The results also explore the effect of reduced CP on total ammoniacal nitrogen (TAN) and of the initial and final CP levels on NH₃ emission reductions. Furthermore, the study also analyses the effect of additional factors such as manure management stages and animal categories on NH₃ emission reductions. The conclusions suggest the need to investigate further questions which would form the basis for discussions at the conference.

## MATERIAL AND METHODS

Our study used a meta-analysis to quantify and compare the effect of a reduction in CP on NH₃ emissions for both cattle and pigs (Sajeev et al. 2017). Since a reduction of CP content in animal diets affects all phases of the manure management chain, we considered emissions from urine and faeces excreted in animal houses, during their storage, and their application to agricultural soils. The emission reductions were calculated relative to the NH₃ emissions during reference CP treatments. Regression analysis was used to determine the relationships between NH₃ emission reductions, TAN reductions and the CP traits (CP reductions, initial CP and final CP levels) along with their associated interactions.

## RESULTS

Results indicate higher mean NH₃ reductions of 17 ± 6% per %-point CP reduction for cattle as compared to 11 ± 6% for pigs. Statistically significant relationships exist between the level of CP reduction, NH₃ emissions and TAN content in manure for both pigs and cattle, with cattle revealing higher NH₃ reductions and a clearer trend in relationships. Manure management stages and pig categories did not indicate a significant influence on NH₃ emission reductions. The results presented help to accurately quantify the effects of NH₃ abatement following

<footnote n="1">¹ Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Germany; ² Institute of System Sciences, Innovation and Sustainability Research and FWF-DK Climate Change, University of Graz, Austria; ³ Division of Livestock Sciences, Department of Sustainable Agricultural Systems, University of Natural Resources and Life Sciences (BOKU), Austria; ⁴ International Institute for Applied Systems Analysis (IIASA), Austria; ⁵ Institute for Environmental Engineering, University of Zielona Góra, Poland</footnote>
reduced CP levels in animal diets distinguishing between animal types and other physiological factors. This is useful
in the development of emission factors associated with reduced CP as an NH₃ abatement option during manure
management.

CONCLUSION AND DISCUSSION

The higher NH₃ reductions in cattle as presented in this study highlight the opportunity to extend concepts of feed optimization from pigs and poultry to cattle production systems to further reduce NH₃ emissions from livestock manure. This is attributed to the greater attention given to optimization of protein supply in pigs relative to cattle and also due to the specific physiology of ruminants to efficiently recycle nitrogen in situations of low protein intake.

The results presented opens up a set of further research questions. The authors would like to use the Nitrogen Workshop as a forum to discuss these questions. For instance: (i) What is the current level of implementation of reduced CP in animal diets as an NH₃ abatement option? (ii) What are the factors that influence the level of implementation of reduced CP in animal diets? (iii) What are the practical implications of lowering CP in cattle diets? Would there be any effect on milk production, meat gain and quality? (iv) How can we incorporate these results in to an emission inventory? (v) Does lowering CP in ruminant diets to abate NH₃ emissions have an influence on methane (CH₄) emissions from enteric fermentation? If so, can these interactions be quantified?

Acknowledgements: E.P.M. Sajeev was supported by the Austrian Science Fund (FWF) under research grant W 1256-G15 (Doctoral Programme Climate Change – Uncertainties, Thresholds and Coping Strategies).

REFERENCES

Bittman, S., M. Dedina, C. Howard, O. Oenema, and M. Sutton. 2014. Options for ammonia mitigation: Guidance from the UNECE Task Force on Reactive Nitrogen. Centre for Ecology and Hydrology, Edinburgh, UK. http://www.clrtap-tfrn.org/sites/clrtap-tfrn.org/files/documents/AGD_final_file.pdf. Accessed 24 October 2017.

Hou, Y., G. L. Velthof, J. P. Lesschen, I. G. Staritsky, and O. Oenema. 2017. Nutrient recovery and emissions of ammonia, nitrous oxide and methane from animal manure in Europe: effects of manure treatment technologies. Environ Sci Technol 51: 375-383.

Sajeev EPM, Amon B, Ammon C, Zollitsch W, Winiwarter W (2018) Evaluating the potential of dietary crude protein manipulation in reducing ammonia emissions from cattle and pig manure: A meta-analysis Nutrient Cycling in Agroecosystems: 110,161-175

Oenema, O., S. Tamminga, H. Menzi, A. Aarnik, and C. Pineiro. 2014. Livestock feeding strategies. In: Bittman, S., et al., (eds), Options for Ammonia Mitigation: Guidance from the UNECE Task Force on Reactive Nitrogen, Convention on Long Range Transboundary Air Pollution. Centre for Ecology and Hydrology, Edinburgh, UK. p. 10-13. http://www.clrtap-tfrn.org/sites/clrtap-tfrn.org/files/documents/AGD_final_file.pdf. Accessed on 24 Oct. 2017

UNECE. 2015. Methane and ammonia air pollution. Policy Brief prepared by the UNECE Task Force on Reactive Nitrogen. Task Force on Reactive Nitrogen, Working Group on Strategies and Review of the UNECE Convention on Long-range Transboundary Air Pollution, Aarhus, DK. http://www.clrtap-tfrn.org/content/methane-and-ammonia-air-pollution. Accessed on 24 October 2017.

UNECE. 2016. Convention of Long-Range Transboundary Atmopsheric Pollution, United Nations Economic Communication for Europe, Geneva, Switzerland. http://ec.europa.eu/eurostat/web/environment/air-emissions-inventories/database. Accessed on 16 November 2016.
# SUPPORTING TRANSITION TO LOW INPUTS PRODUCTION SYSTEMS: ECONOMIC AND ENVIRONMENTAL ASSESSMENT

DEVIENNE S.¹, VERTES F.², GARAMBOIS N.¹, AKKAL-CORFINI N.², DURAND P.², PARNAUDEAU V.²

¹ AgroParisTech, UFR Agriculture comparée, UMR Prodig, France; ² INRA Agrocampus Ouest, UMR SAS, France.

## INTRODUCTION

Livestock farming is an essential activity in many rural areas. When concentrated in intensive highly productive areas (such as Brittany, NL, DK) it is known to generate both positive services and negative impacts (Dumont et al., 2016), in particular on water, air and soil quality, that imply the need for further evolution toward more sustainable agriculture. How to support transition to sustainable farming at farm and territory scales was the question, applied to a case study (Blavet watershed, Brittany, France), by building possible scenario with local stakeholders and assessing their environmental and socio-economic consequences at both scales. We identified connections between production systems and risky nitrogen agricultural practices and explored potential ways to reduce the environmental impact of farms while respecting their economic viability and technical feasibility of changes.

## MATERIAL AND METHODS

The Blavet river drains a 2090 km² watershed located on granitic (west) with slopes and abrupt relief or shale (east) substrates with flat to moderate slopes. Agricultural areas represent about 70% of the total area, with 3700 farms. Dairy production dominates in the north and western part (granite and/or rainy climate) while the median eastern part with higher agricultural potentialities crop (including vegetables) production, being predominant, is mostly combined with dairy, pig or poultry production.

The technical-economic assessment was realised using the agrarian diagnosis method (Cochet and Devienne, 2006) at regional scale, to identify the different types of production systems according to the present and past means of production, thanks to farm surveys. Each production system was characterized as a combination of cropping and livestock systems, whose function logic was explained and economic results assessed and modelled. The N leaching risk of the different cropping systems was assessed by i) calculating annual soil N surplus modulated by a leaching risk coefficient based on soil cover during winter (from 30% under grassland to 100% under bare soil) and ii) Syst'N model (Parnaureau et al., 2012) for a subsample of farming systems and corresponding cropping systems. Principal component analysis was used to identify clusters of crop rotation x leaching risks, on the cropping systems described in the Blavet data basis from enquiries

Each "conventional" production systems (in a first step dairy cattle specialized or mixed with cash crop production) was then related to an economic/autonomous one (EA), based on agro-ecological principles and/or involved in organic farming, in the context of similar production means and soil-climate conditions. In order to model the redesigning of production systems, we conducted an in-depth study of agro-ecological systems currently present in the region. Results presented here focus on economic and N losses assessment for a conventional dairy system and a possible thriftier and more autonomous alternative.

## RESULTS AND DISCUSSION

1. General results for the Blavet watershed: 40 types of production systems (including 19 dairy production systems, 4 of which being EA alternative systems) were identified and characterized. About 630 cropping systems were distributed in 14 clusters crossing a 1st gradient "crop succession with grasslands or not" and a 2nd one corresponding to a N leaching risk gradient (mean values of clusters between 5 and 80 kgN-NO₃·ha⁻¹·yr⁻¹) and "vegetables or not". If dairy production systems differ depending on land type and herd size, which is correlated with equipment level, they share a common forage system operating logic, maize playing a key role in the process
of milk output growth. Depending on the location (shale or granite, wide or narrow interfluve) the share of arable land and maize yields are more or less important as much as the place of maize in the ration (5 to 3 kg per day during grazing season; 90% to 2/3 of the ration in the winter) and the milk yield (9,500-10,000l to 7500-8000l per cow). Inequalities of access to land and equipment lead to large income disparities, with a growing number of economically fragile production systems in the current context of dairy crisis. Cropping systems linked to dairy production systems were distributed in 11/14 clusters (all < 70 kgN-NO₃·ha⁻¹·yr⁻¹).

**2. Possible transition for one type of dairy farming system: technical, economic and N emissions assessments**

We highlight here an example of transition of a dairy production system (DC1) to an EA system (DCEA1) based on grass-legume grasslands without N fertilizer and mostly grazed, with a rotational grazing system. Despite lower milk yields and production, the drastic decrease of inputs and equipment use allows increased economic performances (value-added and income) and lower N emissions, thanks also to better soil cover in winter.

DC1: 35-38ha, milking parlour 2x4
30-40 dairy cows, 9 500 -10 000 l milk per cow
Silo never closed

M // RG-WC₄yrs: 40%

M // W/IRG: 35%

M // W/CC: 25%

M: maize, W: wheat

Mix: triticale+oat+pea; WC & RC: white & red clover; RG & HRG: perennial & hybridum ryegrass

DCEA1: 35-38ha, milking parlour 2x4
40-50 dairy cows, 6 500 l milk per cow
9 months grazing,
silo closed 3 months

RG-WC₇yrs: 45%

M//mix//RG-WC₇yrs: 35%

M//mix//HRG-RC₃yrs: 25%

<figure><img src="image_175.png" /></figure>

<figure><img src="image_176.png" /></figure>

<figure><img src="image_177.png" /></figure>

3 500

Economic results:
Gross product and Value added per ha (£/ha)

1 000

Crops: other IC

Crop protection

Fertilizers

Cattle: other IC

2 000

Cattle feed

3 000

Fuel

Other intermediate

Consumption (IC)

4 000

Value added

5 000

Current system

Consumption

of fixed capital

6 000

Value added

7 000

Current system (DC1)

AE system (DCEA1)

<figure><img src="image_178.png" /><figcaption>and N emissions</figcaption></figure>

**Figure 1:** Comparison of DC1 and DCEA1 on technical, economical assessment (Syst'N results, hatched areas = N-NO₃ leached, dotted areas = N-NH₃ volatilised)

**CONCLUSION**

The agrarian diagnosis coupled with environmental assessment at farm and watershed scales is based on the analyses of local agricultural systems, in their specific biophysical and socio-economic conditions. Redesign is built using knowledge of agro-ecological systems types as declined by local farmers, and can thus be used to decline changing scenario at territory scale. It was applied on dairy production and crop (including industry vegetables) production systems, before to be extended to other productions. In all cases, coupling improvement in both economic and environmental results led to highlight the conditions favoring transitions and to demonstrate that farmers may find it economically advantageous to adopt systemic changes based on agro-ecological principles allowing lower N emissions. Ongoing work will precise territorial impacts of changes at large scale on regional economic and social issues, as well as on N fluxes at watershed scale, while some other impacts or ecosystem services linked to current and alternative production systems will be assessed.

**Acknowledgements:** ANR for Escapade funding, Brittany region and AE Loire-Bretagne for Creseb-Blavet funding

**REFERENCES**

Dumont B. (coord), Dupraz P. (coord.) et al., 2016. Rôles, impacts et services issus des élevages en Europe. Synthèse de l'expertise scientifique collective, INRA (France), 126 p.

Parnaupeau V., Reau R., Dubrulle P., 2012. Un outil d'évaluation des fuites d'azote vers l'environnement à l'échelle du système de culture : le logiciel Syst'N. Innovations Agronomiques 21, 59-70.

Cochet H, Devienne S., 2006. Fonctionnement et performances économiques des systèmes de production agricole : une démarche à l'échelle régionale. Cahiers Agriculture n°6, nov-dec 2006.
# ORGANIC N FERTILIZATION EFFECTS ON PASTURE ESTABLISHMENT AND FOREST FIRE PREVENTION

FERREIRO-DOMINGUEZ N<fnref n="1" />,², RODRIGUEZ-RIGUEIRO J<fnref n="1" />, RIGUEIRO-RODRIGUEZ A<fnref n="1" />, MOSQUERA-LOSADA MR<fnref n="1" />

## INTRODUCTION

Soil fertility is key to ensure high pasture production. Lime and fertilizers usually improves soil chemical properties in acid soils, enhancing herbaceous pasture establishment instead of woody understory vegetation in silvopastoral systems, once established harvest that promotes fire risk and causes people death in South Europe. Once established, grazing or harvesting maintains the dominance of the herbaceous component in the silvopastoral system (Mosquera-Losada et al. 2006). Liming and fertilization also helps to maintain botanical composition of sown grasslands, leading to a better animal grazing and production and, in Galicia, to a clear reduction of forest fire risk. Increasing fertility is usually based on mineral fertilizers that are currently costly for both farmers and the environment due to fertilizer production and transport. Thus, using organic fertilizers easily available and close to the farm should be promoted. Municipal sewage sludge (SS) is a good option to increase pasture production and enhance soil pH of acid soils in Galicia (Mosquera-Losada et al., 2010), but could cause some harmful to the environment due to higher proportion of heavy metals SS has compared with soil, which needs to be evaluated at long term. This study aims at evaluating the effect of three doses of SS (160, 320 and 480 kg total N ha⁻<fnref n="1" />) combined or not with lime, on the botanic pasture composition, compared with control treatments (no fertilisation (NF) and mineral fertilisation (MIN)) during twelve years in a silvopastoral system established under *Pinus radiata* D. Don in Galicia.

## MATERIAL AND METHODS

The study was conducted in Pol (Lugo, Galicia, NW Spain) in a plantation of *Pinus radiata* D. Don established in 1993 (1667 trees ha⁻<fnref n="1" />). In autumn of 1997, an experiment with a randomised block design was carried out in 27 experimental plots (9 treatments x 3 replicates) of 96 m². Each plot was sown with a mixture of *Lolium perenne* L., *Dactylis glomerata* L. and *Trifolium repens* L. after ploughing. All plots were initially fertilised with 120 kg P₂O₅ ha⁻<fnref n="1" /> and 200 kg K₂O ha⁻<fnref n="1" />. The nine treatments were: three SS doses (160 (L1), 320 (L2) and 480 (L3) kg total N ha⁻<fnref n="1" />) with or without liming applied in 1997 before sowing (2.5 t CaCO₃ha⁻<fnref n="1" />) applied in 1998, 1999 and 2000, a no fertilization (NF) treatment as unfertilized control in the limed and unlimed plots and a mineral treatment (MIN) control in the unlimed plots (500 kg of 8% N – 24% P₂O₅ – 16% K₂O ha⁻<fnref n="1" /> and year from 1998 to 2003). To evaluate the residual effect of SS treatments, the same mineral fertiliser doses were added in 2001, 2002 and 2003 in the previously SS fertilised plots. The botanical composition of the pasture was estimated by random sampling of pasture (4 per plot, each0.3 × 0.3 m²) during spring and winter from 1998 to 2012. Samples included pine needles on soils and were separated into the different species by hand in the laboratory. This study shows the data obtained in spring 1998, 2004 and 2012. The data were analysed using ANOVA (proc glm procedure). Means were separated by using LSD test, if ANOVA was significant.

## RESULTS AND DISCUSSION

Pasture production was reduced from the beginning to the end of the experiment. Shortly after being sown (1998), both *Trifolium* and *Lolium* responded positively to liming, and *Lolium* was better established when liming was combined with L3. *Trifolium repens* L. and *Lolium perenne* L. were generally better established in limed and SS fertilized plots (Figure 1) as these treatments improve soil fertility, pasture productivity and quality (Mosquera-Losada et al., 2009) probably due to the pH increase (Bailey, 1995). Dactylis response was better when higher SS doses (480 kg N ha⁻<fnref n="1" />) were applied but disappeared after 2004 in both the unlimed NF and the MIN plots. Both *Lolium* and *Trifolium* disappeared in all treatments four years after the last SS fertilization, probably due to the

<footnote n="1">¹ Department of Crop Production and Engineering Projects, Escuela Politécnica Superior de Lugo, University of Santiago de Compostela, Campus Universitario s/n, 27002 Lugo, Spain ² Forest Research Centre, School of Agriculture, University of Lisbon, Tapada da Ajuda s/n, 1349-017 Lisbon, Portugal</footnote>
high water soil acidity (4.5) and to the increase of canopy cover caused by the Pine growth. Spontaneous vegetation, including weeds and shrubs, was in a greater proportion in control treatments (NF) compared to SS treatments enhancing more fertility demanding sowed species. The larger proportion of major shrubs (i.e. gorse) is usually linked to a high fire risk, as shown by different studies indicating that an increase in soil fertility can change the botanical composition of the understory by highly decreasing flammable shrub species (Ferreiro-Domínguez et al., 2014). Other species are mainly associated to spontaneous pasture species (i.e. Agrostis spp..) with low feed quality. The higher proportion of needles replacing the pasture obtained in SS fertilized plots could be explained by the trees enhanced growth, whose canopy cover prevented solar radiation to attain the lower stratum, limiting the decomposition and mineralization due to low temperatures and increasing the needle accumulation in the top soil.

<figure><img src="image_179.png" /><figcaption>Figure 1. Botanical composition under different treatments in 1998, 2004 and 2012, where NF: no fertilization; L1: low SS dose (160 kg N ha⁻¹); L2: medium SS dose (320 kg N ha⁻¹); L3: high SS dose (480 kg N ha⁻¹); MIN: 500 kg ha⁻¹ of 8:24:16; Dg: Dactylis glomerata L.; Lol: Lolium perenne L.; Tri: Trifolium repens L.; Dry: senescent material.</figcaption></figure>

## CONCLUSION

Sewage sludge favoured the establishment of sown species increasing pasture quality and reducing the fire risk. Thinning should be carried out to enhance pasture production and reduce needle accumulation in the top soils once canopy cover is complete.

**Acknowledgements:** We are grateful to XUNTA DE GALICIA (Consolidation funds and Consellería de Cultura, Educación e Ordenación Universitaria (“Programa de axudas á etapa posdoutoral DOG nº122, 29/06/2016 p.27443, exp: ED481B 2016/0710”)).

## REFERENCES

* Bailey, J.S., 1995. Liming and nitrogen efficiency: Some effects of increased calcium supply and increased soil pH on nitrogen recovery by perennial ryegrass. Commun. Soil Sci. Plant Anal. 26, 1233-1246.

* Ferreiro-Domínguez, N., Rigueiro-Rodríguez, A., Bianchetto, E., Mosquera-Losada, M.R., 2014. Effect of lime and sewage sludge fertilisation on tree and understory interaction in a silvopastoral system. Agric. Ecosyst. Environ. 188, 72-79. https://doi.org/10.1016/J.AGEE.2014.02.007

* Mosquera-Losada, M.R., López-Díaz, M.L., Rigueiro-Rodríguez, A., 2009. Zinc and copper availability in herbage and soil of a Pinus radiata silvopastoral system in Northwest Spain after sewage-sludge and lime application. J. Plant Nutr. Soil Sci. 172.

* Mosquera-Losada, M.R., McAdam J., Rigueiro-Rodríguez, A., 2006. Silvopastoralism and sustainable land management. CABinternational.

* Mosquera-Losada, M.R., Muñoz-Ferreiro, N., Rigueiro-Rodríguez, A., 2010. Agronomic characterisation of different types of sewage sludge: Policy implications. Waste Manag. 30, 492-503.
# PASTURE PRODUCTION IN A SILVOPASTORAL SYSTEM ESTABLISHED WITH JUGLANS REGIA L. AND FERTILIZED WITH SEWAGE SLUDGE

MOSQUERA-LOSADA, M.R.<fnref n="1" />, ARIAS-MARTINEZ, D.<fnref n="1" />, RIGUEIRO-RODRÍGUEZ A<fnref n="1" />, FERREIRO-DOMINGUEZ, N.<fnref n="1" />, ²

## INTRODUCTION

Nitrogen can be applied to the soil trough inorganic and organic fertilisers. Inorganic fertilisers are costly from both economic and environmental points of view. The use of sewage sludge (SS) as organic fertiliser is encouraged by the European Community since it can have valuable agronomic properties (EU, 1986), but SS can have higher levels of heavy metals than the soil, which could be a risk. In Europe, SS should be stabilised before applying it into the soils. The main forms of stabilisation are anaerobic digestion, compost and pelletisation. Silvopastoral systems, which are characterized by integrating woody vegetation with forage and livestock production in the same area, can modify the pasture production by the fertilisation with SS but also by the tree density (Mosquera-Losada et al., 2011). The aim of this study was to evaluate the effect of three types of SS (anaerobic, composted and pelletised) on pasture production compared with control treatments (no fertilisation and mineral fertilisation) in a silvopastoral system established under *Juglans regia* L. at different densities (277 and 625 trees ha⁻<fnref n="1" />).

## MATERIAL AND METHODS

The study was conducted in A Mota (Boimorto, A Coruña, Spain) with an Atlantic climate. At the beginning of the experiment soil pH was acidic (6.28), the texture loam and the bulk density 984.24 kg m⁻³. In 2013, the plot was planted with *J. regia* L. at low (LD: 277 trees ha⁻<fnref n="1" />) and high tree density (HD: 625 trees ha⁻<fnref n="1" />) and sown with *Dactylis glomerata* L., *Lolium perenne* L. and *Trifolium repens* L. The experimental design was randomized blocks, with three replicates and five fertilisation treatments per each tree density. Treatments consisted of no fertilisation (NF), mineral fertilisation (MIN) with 500 kg of 8% N – 24% P₂O₅ – 16% K₂O ha⁻<fnref n="1" /> and year and fertilisation with anaerobic (ANA), composted (COM) and pelletised (PEL) SS (320 kg total N ha⁻<fnref n="1" />) before tree planting and a second application of MIN in February 2015 (250 kg of 10% N – 10% P₂O₅ – 20% K₂O ha⁻<fnref n="1" /> and year). The plots were grazed by sheep in a continuous stocking system. Pasture production was estimated by taking several samples of pasture per plot within an exclusion cage of 1 m² from 2014 to 2017. The samples were weighed in fresh in the field and a sub-sample was taken to the laboratory, weighed and dried (48 hours at 60°C) and weighed again to determine the dry matter production. Annual pasture production in 2015 and 2016 was calculated by summing all harvests in each year. The data were analysed using a repeated measures ANOVA (proc glm procedure). Means were separated by using LSD test if ANOVA was significant (SAS, 2001).

## RESULTS AND DISCUSSION

In this experiment, in both tree densities, pasture production was higher in the 2015 harvest than in 2016 (p<0.001) probably because, despite being 2015 a dry year in general, the mean temperature in 2015 was only 1 °C higher than the last 30 years mean temperature compared with the difference of 16 °C higher of 2016. In any case, the pasture production of this study was similar to the pasture production estimated by Mosquera-Losada et al. (2011) in a similar area. Throughout the study period, the pasture production was significantly higher in LD than in HD (LD: 13.93ª and HD: 12.68ᵇas Mg ha⁻<fnref n="1" />) (different superscript letters indicate significant differences between tree densities) (p<0.01). This result could be explained by the higher shade generated by trees and the higher competition by water and nutrients between trees and pasture in HD than in LD, which indicates that tree thinning would probably help to increase the pasture production in HD. Finally, under trees established at LD, the fertilisation treatments significantly modified the pasture production in April 2015 and August 2017 harvests (p<0.05) (Figure 1). In April 2015, pasture production was higher in –ANA and COM than in NF, and PEL probably

<footnote n="1">¹ Department of Crop Production and Engineering Projects, Escuela Politécnica Superior de Lugo, University of Santiago de Compostela, Campus Universitario s/n, 27002 Lugo, Spain; ² Forest Research Centre, School of Agriculture, University of Lisbon, Tapada da Ajuda s/n, 1349-017 Lisbon, Portugal</footnote>
because ANA COM implies higher inputs of organic matter into the soil, due to its low nitrogen content, that could increase water availability (Mosquera-Losada et al., 2010). However in August 2017, pasture production generally increased with PEL and ANA compared with the other treatments, probably because PEL and ANA increases the availability of N into the soil, and also the liberation of cations (Mosquera-Losada et al., 2010). In the case of the HD, results tended to be similar to those observed in LD (data not shown).

<figure><img src="image_180.png" /><figcaption>Figure 8: Pasture production (Mg dry matter ha⁻¹) in all treatments under low tree density (LD). The right chart shows the production in the two harvests with significant differences. NF: no fertilisation, MIN: mineral; ANA: anaerobic sludge; COM: composted sludge and PEL: pelletised sludge. * indicates that in that harvest there were significant differences between treatments. Different letters indicate significant differences between fertiliser treatments in each harvest.</figcaption></figure>

## CONCLUSION

Pasture production was increased with low tree densities and influenced by the type of fertilization when weather conditions allowed it. COM and ANA use to have higher production during spring due to the organic matter they provide, that increases drought deficiencies resilience, while in summer PEL is the type of fertilization that better performs in terms of pasture production. The use of sewage sludge improves the agronomic benefits compared with NF and promoting bioeconomy while solving problems of residue management.

**Acknowledgements:** We are grateful to XUNTA DE GALICIA (Consolidation funds and Consellería de Cultura, Educación e Ordenación Universitaria) ("Programa de axudas á etapa posdoutoral DOG nº122, 29/06/2016 p.27443, exp: ED481B 2016/0710")).

## REFERENCES

* EU, 1986. Council Directive 86/278/EEC of 12 June 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture, 181.

* Mosquera-Losada, M.R., Morán-Zuloaga, D., Rigueiro-Rodríguez, A., 2011. Effects of lime and sewage sludge on soil, pasture production, and tree growth in a six-year-old Populus canadensis Moench silvopastoral system. J. Plant Nutr. Soil Sci. 174, 145-153. https://doi.org/10.1002/jpln.200900231

* Mosquera-Losada, M.R., Muñoz-Ferreiro, N., Rigueiro-Rodríguez, A., 2010. Agronomic characterisation of different types of sewage sludge: Policy implications. Waste Manag. 30, 492-503. https://doi.org/10.1016/j.wasman.2009.09.021

* SAS, 2001. SAS/Stat User's Guide: Statistics. SAS Institute Inc., Cary, NC, USA.
N₂O EMISSIONS FROM CROP RESIDUES VARY GREATLY WITH RESIDUE QUALITY AND MANAGEMENT

OLESEN, J.E.¹, RECOUS, S.², HANSEN, S.³, JENSEN, E.S.⁴, BUTTERBACH-BAHL, K.⁵, REES, R.M.⁶, BLEKEN, M.A.⁷,
SMITH, K.E.⁸, ERNFORS, M.⁴, LAVILLE, P.², LASHERMES, G.², LOUBET, B.², MASSAD, R.², PETERSEN, S.O.¹,
THORMAN, R.E.⁸, TAGHIZADEH-TOOSI, A.¹, TOPP, C.F.E.⁶

¹ Aarhus University, Denmark; ² INRA, France; ³ NORSØK, Norway, ⁴ SLU, Sweden, ⁵ KIT, Germany, ⁶ SRUC, UK, ⁷ NMBU, Norway, ⁸ ADAS, UK

INTRODUCTION

The nitrogen (N) content of crop residues is used in national greenhouse gas (GHG) emission inventories to estimate nitrous oxide (N₂O) emissions from agriculture. Crop residues also make a major contribution to sustaining or enhancing soil carbon (C) stocks and soil fertility. Depending on the amount of C and N in crop residues and their contributions to N₂O emissions or to the soil C and N balance, residues might increase or decrease the GHG footprint of agricultural systems. In 2015, 21.7 Mt CO₂e were released as N₂O from agricultural crop residues in EU (EEA, 2017), making it the third largest source of direct N₂O emissions from agricultural soils. Yet the quantification of this source has largely been neglected, so that the current estimations of N₂O emissions from crop residues are associated with some of the largest uncertainties in national GHG inventories. These uncertainties relate to: 1) the amount and N concentration of the returned residue; 2) the magnitude of N₂O emissions associated with the application of crop residues of different quality to soils; and 3) how N₂O emissions and uncertainties differ with crop species, soils, climate and management practices. Recent studies suggest that the concurrent C and N transformations are critical for N₂O emissions from crop residues.

MATERIAL AND METHODS

A new European research project (ResidueGas), started in autumn 2017, will address the estimation of N₂O emissions from crop residues, including cover crops and incorporation of grassland swards. The project aims to:

* propose a new and improved methodology to estimate N₂O emissions associated with crop residues for the most important cropping systems in Northern Europe, for use in national emissions inventories.

* assess the relative importance of crop residue management for total N₂O emissions and the C and N balance of agricultural soils across different cropping and residue management systems for various pedoclimatic conditions, as a basis for the identification and implementation of mitigation strategies.

ResidueGas will suggest a new method to account for N₂O emissions from soil receiving crop residues through reviewing existing findings and data, targeted experimental studies for Europe, and improved modelling, suggest a new method to account for N₂O emissions from soil receiving crop residues. Furthermore, ResidueGas will evaluate the mitigation potential of a combination of practices on soil organic carbon (SOC) storage and N₂O emissions from residue incorporation and develop new software tools that will assist in identifying the best mitigation options. An improved understanding of underlying processes will help further developing biogeochemical models for simulating N₂O emissions and SOC storage, and testing these effects under field conditions. The improved models will be used as the basis for developing a residue-targeted decision support system, for estimating soil N₂O and SOC changes in typical crop rotations, soils and agro-environmental zones in Europe. Simulations will be aggregated into a meta-model representing a simplified, but greatly improved and operational approach to estimate residues effects on soil N₂O emissions and SOC stocks.

RESULTS AND DISCUSSION

Preliminary hypotheses in the ResidueGas project illustrate the importance of critical moments during crop management cycles for N₂O emissions from crop residues. High N₂O emissions have been associated with low residue C:N ratios (Charles et al., 2017), but residue C and its degradability are also important for emissions (Li et al., 2016), and in some cases may be a more significant driver than total N input (Pugesgaard et al., 2016). This
indicates that crop residue properties, beyond N supply, such as chemical composition, and the mode of residue
applications to soils influence N₂O emissions, and that C and N availability in residues as well as management need
to be considered. The following components of cropping systems, which may be particularly at risk for large N₂O
emissions and should be better studied for inclusion in inventories and for mitigation:

* Incorporation of fresh crop residues after harvesting in summer or autumn of vegetative crops, like vegetables, potatoes and sugar beet

* Winter periods where crop residues remain on the soil surface (not incorporated). Effects are linked to timing of soil tillage and the effects of freeze-thaw on decomposition and N₂O fluxes at low temperature.

* Incorporation in spring of N-rich residues of cover crops, in particular when these cover crops are ploughed and this is associated with addition of N in mineral fertilisers or manure.

* Cover crops that are frost killed during winter (e.g. Brassica species) giving conditions for decomposition of degradable C and N compounds, and thus for N₂O emissions.

* Termination of grasslands (in particular grass-clover swards) where degradable C and N in the incorporated plant materials can support denitrification.

The effects of crop residue quality on N₂O emissions is anticipated to be linked to soil type and soil properties, as well as the method and timing of residue incorporation in soil (Li et al., 2015). Crop residue management is only to a very limited extent included as part of policy measures to reduce agricultural GHG emissions. Emissions reductions can only be effectively incentivized and implemented as mitigation measures, if there are documented and verified effects of mitigation options reflected in national inventories, and if uncertainties can be significantly reduced. Such efforts require focus on the critical moments for N₂O emission identified above.

CONCLUSION

Current IPCC methodology to estimate N₂O emissions from crop residues fails to capture the large variability in quality of the crop residues, where emissions of N₂O are not only related to the N availability of the crop residues, but also to the availability of degradable carbon enhancing microbial activity and oxygen demand that, in turn, contribute to determining the denitrifying environment in the soil.

**Acknowledgements:** ResidueGas is funded through the ERA-GAS network partly by the EU Horizon 2020 programme and partly by national funding bodies.

REFERENCES

EEA, 2017. Annual European Union greenhouse gas inventory 1990–2015 and inventory report 2016. EEA Report No 15/2016.

Charles, A., Rochette, P., Whalen, J.K., Angers, D.A., Chantigny, M.H., Normand, B., 2017. Global nitrous oxide emission factors from agricultural soils after addition of organic amendments: A meta-analysis. Agric. Ecosyst. Environ. 236, 88-98.

Li, X., Petersen, S.O. et al., 2015. Effects of contrasting catch crops on nitrogen availability and nitrous oxide emissions in an organic cropping system. Agric. Ecosyst. Environ. 199, 382-393.

Li, X., Sørensen, P., Olesen, J.E., Petersen, S.O., 2016. Evidence for denitrification as main source of N₂O emission from residue-amended soil. Soil Biol. Biochem. 92, 153-160.

Pugesgaard, S., Petersen, S.O., Chirinda, N., Olesen, J.E., 2017. Crop residues as driver for N₂O emissions from a sandy loam soil. Agric. For. Meteorol. 233, 45-54.
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