European Commission Ref. 070201/2014/693666/FRA/ENV.C.3 Service Agreement 7:
Continued improvements of inventory methodologies
Task 3.3: Ammonia emissions from standing crops
Task lead: J Webb, Ricardo-AEA
Consultation paper for discussion
1. Context
Ricardo-AEA Ltd, Aether Ltd and AMEC have been commissioned to investigate and propose
improvements to inventory methodologies in a number of key areas identified by the Task Force on
Emission Inventories and Projections (TFEIP) and other bodies. The European Commission, as
part of a collaborative initiative, has provided funding for this project, which is expected to be the
focus of discussion at the TFEIP meeting and workshops in May 2015.
Among the following priority areas of the GB chapters for agriculture the project aims to bring up to
date is ammonia (NH3) emissions from standing crops
2. Issues to be addressed
Emissions of NH3 from crops mainly occur due to the increase in the concentration of N in the
leaves of crops following the addition of fertilizer-N. In consequence it is often difficult to separate
the direct fertilizer and plant emissions in practice, since both are a function of fertilizer-N supply,
and in many experiments total emissions were measured. The direct emissions of NH 3 that have
been measured from crops have been attributed to enrichment of the apoplast with NH 4+. This
enrichment can occur following addition of fertilizer-N but may also occur from cereal crops during
grain-filling if drought or other adverse environmental impacts reduce photosynthesis, or if the crop
becomes diseased, leading to insufficient carbohydrate for protein formation. However, as well as
being influenced by air concentration and environmental conditions, both emission and deposition
occur on diurnal cycles.
Foliar emissions are expected to be larger from annual cereal crops than from fertilized agricultural
grassland, since much of the emission may occur during the grain ripening and vegetation
senescence phase. Crop emissions appear to be rather small on an area basis; emissions of
1-2 kg N ha-1 early in the season have been reported.
There have been few data from standing crops to justify establishing a default EF. These
considerations mean that it is difficult to obtain accurate estimates of crop emissions and the data
are currently considered too uncertain to establish separate default EFs for this source. In the Tier
1 and 2 methodologies currently used in the GB, the EFs used include direct emission from N
fertilizer together with any emission from foliage that occurs immediately following application. The
only exception is the emission from cultivated legumes, since N fertilizers are not usually applied to
legumes and hence any measured emissions of NH3 can only arise from the crop. For these a
separate, tentative default EF is provided. Any proposals for calculating discrete NH 3 emissions
from non-leguminous crops will need to ensure there is no double-counting, i.e. that the crop
emissions are only those that take place after emissions from applied N fertilizers have stopped.
Emission of NH3 from standing crops has been discussed frequently at TFEIP meetings and was
recently identified as an area where greater collaboration with the modelling community was
required. The objective of Task 3ii is to review existing information concerning NH 3 from standing
crops, and develop appropriate methodologies for the Guidebook, in close working cooperation
with the international air quality modelling community.
3. Proposed approach
The work will be carried out by means of a literature review. A key reference to use as the starting
point for the review will be that of Asman (2009). At the time of publication there were only a very
few published estimates of emissions from crops throughout the whole growing season. Our review
will therefore be of peer-reviewed papers and reports identified through the EAGER and TFEIP
networks.
Ricardo-AEA, Aether and AMEC Foster Wheeler
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Continued improvements of inventory methodologies: Task 3.3 Consultation Paper
As indicated above, a key aspect of identifying NH 3 emissions from standing crops will be to
distinguish emissions originating within the crop themselves from emissions from applied N
fertilizer. This distinction is relatively easy to make with respect to arable crops as nitrogen
fertilizers are applied on only 1 to 3 occasions and NH 3 emissions following N fertilizer application
usually decrease to background levels within 7 to 10 days after application as the fertilizer-N enters
the soil matrix.
Asman (2009) proposed a net annual emission of 3.0 kg/ha NH3-N for winter wheat, spring barley,
oilseed rape and grain legumes in order to estimate direct emissions of NH 3 from standing crops in
The Netherlands. A key factor likely to affect NH3 emissions from standing crops is the level of N
fertilizer applied. However, Asman (2009) reported that the limited evidence available did not
confirm this. Factors that are likely to affect direct crop emissions of NH 3 include drought, disease
and other factors that prevent crops from reaching their yield potential.
Identifying discrete crop emissions from grassland is much more difficult. First, N fertilizer
applications may be made on up to 6 occasions during the growing season meaning that emissions
from N fertilizer will be taking place for between 6 and 8 weeks of the season. In addition most
grassland is grazed and emissions will arise from excreta deposited during grazing. It is likely
therefore that data will only be available for emissions from grassland cut for hay and silage. The
review will ensure that reported emissions from grass cut for forage crops and left to dry in the field
will not be included as these emissions are attributed to crop residues.
4. Key sources of data
A key source of data will be:

Asman, W.A.H. 2009. Ammonia emission from crops, grass and crop residues. Report
written for the National Institute for Public Health and Environment (RIVM), Bilthoven, The
Netherlands. Report R-2009-01.
This report will be used as the starting point for the literature review.
5. Your views
Your views are sought on the following key issues:
Ammonia emissions from standing crops are determined by the concentration difference between
the plant tissues and the atmosphere, and the resistance to transport from plant tissues to
atmosphere.

Much is known about atmospheric concentration (modelled at least).

Less is known about plant concentrations, especially in the tissues close to the stomatal
cavity.
It would help us if you are able to inform us of the availability of models/measurements you are
aware of that may be used to predict net emissions from crops.
6. Consultation programme
An introductory discussion has been held with the TFEIP management group at their meeting on
11 February 2015. The work will be discussed at the EAGER meeting on 16-17 April 2015.
Consultation with TFEIP members is planned to take place during the TFEIP meeting and
workshop in May 2015. Following this, the project team will develop draft methodologies and
Guidebook text. This will be circulated for consultation in late 2015, working with the TFEIP Expert
Panel co-chairs.
Thank you for your co-operation with this process.
Date: 24 April 2015
Version no. 03
Ricardo-AEA, Aether and AMEC Foster Wheeler
Issue no. 03
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