WP2 The effect of N fertiliser forms on nitrous oxide

Transcription

NT2605 Final report WP2 Nitrous oxide emissions
________________________________________________________________________________
Component report for Defra Project NT2605 (CSA 6579)
WP2 The effect of N fertiliser
forms on nitrous oxide
emissions
Lead Authors
Keith Smith and Karen Dobbie (Edinburgh University)
Rachel Thorman (ADAS)
and
Sirwan Yamulki (IGER)
February 2006
NT2605 Final report Nitrous oxide emissions.doc
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Contents
1. EXECUTIVE SUMMARY………………………………………………………………………………….4
2. INTRODUCTION…………………………………………………………………………………………...5
3. EXPERIMENTAL DESIGN, TREATMENTS AND METHODS………………………………...……11
4. RESULTS………………………………………………………………………………………………….14
5. DISCUSSION…………………………………..……………………………………………………….…25
6. KEY CONCLUSIONS…………………………………………………………………………………….27
7. REFERENCES……………………………………………………………………………………………28
8. APPENDICIES…………………………………………………………………………………………….31
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Abbreviations
Ag
AnA
AN
AS
nBTPT
CAN
CEC
DCD
DNDC
EF
EU
FFD
GC
HRI
IGER
IPCC
N
NH3
NH4
N2O
NO2
NO3
NVZ
QuB
RR
U
U+Ag500c
U+Ag1000c
U+Ag250m
U+Ag500m
UAN
UAN+Ag500
UAN+Ag1000
UAS
UKAEI
WFPS
ppmv
Agrotain (trade name) urease inhibitor (active ingredient is nBTPT)
Anhydrous ammonia
Ammonium nitrate
Ammonium sulphate
N-(n-butyl)-thiophosphoric triamide urease inhibitor
Calcium ammonium nitrate
Cation exchange capacity
Dicyandiamide nitrification inhibitor
DeNitrification - DeComposition
Emission factor
Edinburgh University
Freshwater Fish Directive
Gas chromatography
Horticulture Research International
Institute of Grassland and Environmental Research
Intergovernmental Panel on Climate Change
Nitrogen
Ammonia
Ammonium
Nitrous oxide
Nitrite
Nitrate
Nitrate Vulnerable Zone
Queens University, Belfast
Rothamsted Research
Urea
Urea granules with 500 mg/kg of nBTPT urease inhibitor (coated onto
granule)
Urea granules with 1000 mg/kg of nBTPT urease inhibitor (coated onto
granule)
Urea granules with 250 ppm of nBTPT urease inhibitor (in the melt)
Urea granules with 500 ppm of nBTPT urease inhibitor (in the melt)
Urea ammonium nitrate solution
Urea ammonium nitrate solution with nBTPT urease inhibitor (500 ppm of
nBTPT)
Urea ammonium nitrate solution with nBTPT urease inhibitor (1000 ppm of
nBTPT)
Urea ammonium sulphate
UK Ammonia Emissions Inventory
(Soil) water-filled pore space
gas concentration in parts per million by volume (equivalent to mol mol-1)
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1. Executive Summary

Nitrous oxide (N2O) is an important greenhouse gas and contributes about 6% of the
global warming potential of all UK greenhouse gas emissions. Agriculture contributes an
estimated 67% of UK N2O emissions, of which fertiliser-N directly contributes about 25%.
Use of fertiliser-N in UK agriculture therefore contributes about 2% of all greenhouse gas
emissions.

Nitrous oxide emissions were measured by the closed static chamber method following
the application of ammonium nitrate (AN) and urea based fertilisers at RB209
recommended rates. Measurements of N2O were made at two grassland sites and one
arable site in 2004, and at one grassland and two arable sites in 2005.

Taking the results from the NT2603 and NT2605 programmes together, the conclusion
reached after the former, that the data broadly bear out the relationships obtained in
earlier studies for Defra, remains the same. The results show a strong dependence of
N2O emission on soil wetness, temperature and the presence of sufficient mineral N in
the soil, which decreases rapidly after N application, mainly as a result of plant uptake.

In only one of the 2004/2005 experiments reported here, and in one in 2003 (NT2603
report) was there a significant decrease in N2O emissions through applying urea instead
of AN, although in 2003 there were another two experiments where the decrease through
using urea instead of CAN was also significant. However, if expected indirect emissions
of N2O following volatilisation and redeposition of ammonia are taken into account, then
total emissions from AN were no greater than from urea.

The ratio of the EFs for N2O emissions from urea modified by the addition of Agrotain to
the EFs for unmodified urea tended to decrease as the actual EFs increased. However,
even with the addition of a further 6 sites in 2004/2005 to the 6 sites investigated in 2003,
there are still too few data to give a very robust assessment of the direct emissions
associated with these new fertiliser materials, as compared with those from unmodified
urea. However, the use of Agrotain appears to offer some potential for reducing indirect
N2O emissions, since it also reduces volatilisation losses of ammonia.
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2. Introduction
2.1. The NT26 Research Programme
The NT26 research programme was set up by Defra to investigate the nitrogen (N) loss
pathways, the environmental and economic impacts, and the response of agricultural and
horticultural crops to different forms of fertiliser-N. The NT2605 project was part of a suite of
projects in this programme as shown below (Final report submission dates shown in
brackets).
NT2601
Desk study reports on:
 Nitrogen fertilising materials (June 2003)
 Production and use of nitrogen fertilisers (August 2003)
NT2602
Desk study report on:
 Evaluation of urea-based nitrogen fertilisers (October 2003)
NT2603
Report of field studies (2002/03 cropping season):
 The behaviour of some different fertiliser-N materials (March 2004)
NT2604/06
Facilities construction:
 Ammonia emissions from nitrogen fertilisers – wind tunnel construction
(March 2004)
NT2605
This project
NT2610
Report of field studies (led by Silsoe Research Institute):
 Spreading accuracy of solid urea fertilisers (August 2005)
The following leading UK agri-environment research organisations participated in all the
NT26 projects (except NT2610), including the NT2605 project reported here.







ADAS UK Ltd
Edinburgh University (EU)
Warwick HRI (HRI)
Institute of Grassland and Environmental Research (IGER), North Wyke
Queens University, Belfast (QuB)
Rothamsted Research (RR)
SAC Commercial Ltd (SAC)
The project was led by Peter Dampney, Principal Research Scientist, ADAS Boxworth
Research Centre, Cambridge who was the main point of contact with the Defra NT26
Steering Group.
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2.2 The NT26 Project
The NT2601, NT2602 and NT2603 projects provided the basis for the field experimental and
other work carried out in NT2605, in cropping seasons 2003/04 and 2004/05. The overall
aim of the project was to develop working decision support systems (DSS) to evaluate the
agronomic, environmental and economic impacts that would result from changes in the use
of different fertiliser-N materials in UK agriculture. More specifically, project work packages
(WP) covered the following topic areas:-
WP1a
To investigate crop responses to different fertiliser N forms.
WP1b
To generate robust ammonia emission algorithms and emission factors for
predicting the loss of ammonia following application of different fertiliser N
forms under a range of crop, soil and environmental conditions. To evaluate
the relationship between ammonia loss and crop N use efficiency as a
potential basis for revising current national standard nitrogen fertiliser
recommendations (Defra, 2000).
WP2
To generate robust nitrous oxide emission factors for predicting losses
following application of different fertiliser N forms under contrasting crop, soil
and environmental conditions.
WP3
To determine the optimum formulation method, addition rate and method of
use of urea treated with the urease inhibitor nBTPT (Agrotain), to
maximise its ammonia abatement potential and efficiency of N use by crops,
whilst minimising any adverse phytotoxic effects.
WP4
To assess the risk of ammonium-N, nitrite-N or urea-N losses to surface
waters and groundwaters following the application of urea-based N
fertilisers.
WP5
To assess the potential for urea or urea+Agrotain to cause phytotoxic
effects during establishment, in growing crops, or in marketable produce.
WP6
To construct a decision support system that will assess the economic
impacts of changes in the availability of different forms of N fertiliser on
different farm types and UK agriculture.
WP7
To estimate and evaluate the agronomic, environmental and economic
impacts at both farm and national levels that would result following different
hypothetical scenarios concerning the availability of N-containing fertilisers
to UK farmers.
Reporting of the NT2605 has been structured into a suite of 8 component reports, one for
each work package plus an over-arching Executive Summary for the whole project. Each
report is self contained with its own Executive Summary, but interacts with data and
conclusions from other WPs where appropriate.
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2.3. Work Package 2
Nitrous oxide (N2O) is an important greenhouse gas and contributes about 6% of the global
warming potential of all UK greenhouse gas emissions. Agriculture contributes an estimated
67% of UK N2O emissions, of which fertiliser-N directly contributes about 25%. Use of
fertiliser-N in UK agriculture therefore contributes about 2% of all greenhouse gas emissions.
The main objective of this work was to assess the likely impact of an increase in the use of
urea fertilisers in UK agriculture on N2O emissions. In addition, the effect of adding a urease
inhibitor (Agrotain) to urea fertiliser on N2O emissions was examined.
The main agricultural sources of nitrous oxide include emissions from soils after application
of inorganic and organic forms of nitrogen (N) as synthetic fertilisers, crop residues, manures
or composts, as well as emissions from livestock operations, whether from animal housing,
from manure storage, or following direct deposition of urine and faeces to soils during
grazing. Nitrogen-fixing crops, whether grain legumes such as soyabeans or fodder crops
such as clover or alfalfa, often introduce large quantities of N into soils, and some of this also
can be lost to the atmosphere as N2O. These sources have been extensively reviewed by,
for example, Granli and Bøckman (1994), Mosier and Kroeze (1999), Bouwman et al.
(2002a,b), and Rochette and Janzen (2005).
In addition to the direct sources of N2O, there are also indirect ones that include N deposited
onto land surfaces following ammonia and NO x volatilisation, and nitrate leaching from
agricultural land in drainage water, passing into aquifers or into surface waters and their
sediments, where it can be partially transformed to N2O (e.g. Mosier et al., 1998, Reay et al.,
2004; Denier van der Gon and Bleeker, 2005).
The total N2O emissions from direct and indirect agricultural sources are believed to have
increased dramatically during the last few decades, in association with the increasing use of
N as a means of increasing crop yields (Mosier et al., 1998).
2.3.1 Effect of fertiliser form
The Intergovernmental Panel on Climate Change (IPCC) recommend a “default value” for
the N2O emission factor (EF) for direct emissions from agricultural land of 1.25% of the N
applied, whether as synthetic fertiliser, organic manure, or N contained in ploughed-in crop
residues (IPCC, 1997; Mosier et al., 1998). This is based on the review of published work at
the time by Bouwman (1996). More recently a mean value for emissions of 0.9% has been
estimated by Bouwman et al. (2002a,b) and Stehfest and Bouwman (in press), based on
much expanded data sets, and the IPCC are expected to agree shortly on a revised default
EF rounded to 1.0% (K.A. Smith, pers. comm.)
The default indirect EFs are 1.0% of N deposited from the atmosphere, and 2.5% of N lost to
watercourses by leaching or runoff (IPCC, 1997; Mosier et al., 1998). The latter value is also
in the process of being revised downwards, to 1.25% (K.A. Smith, pers. comm.). Hence to
fully assess the impact of different types of fertiliser on N 2O emission, account needs to be
taken not just of direct N2O emissions, but also of any associated differences in emissions of
ammonia and nitrate leaching.
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The default procedure (IPCC, 1997; Mosier et al., 1998) does not recognise any difference in
EFs between fertiliser forms. In another review, Granli and Bøckman (1994) summarised the
median N2O “yields” (EFs) for different types of N fertiliser, which had been compiled in five
earlier papers. They concluded that N2O EFs were usually between 0.1 and 2%, with no
obvious difference between fertiliser types, except for anhydrous ammonia, for which higher
EFs had been reported. However, pooling data from all available studies can hide significant
differences that occur under some circumstances, and Granli and Bøckman (1994)
concluded that the following situations can be associated with high N2O EFs:

Application of urea/ammonium compounds under conditions favouring N2O production by
both nitrification and denitrification, e.g. in moist but well-aerated soil.

Use of nitrate fertilisers where denitrification is favoured, e.g. on clay soils in wet
climates.

Injection of anhydrous (but not aqueous) ammonia.
Harrison and Webb (2001) analysed the literature that had become available up to 1998/9,
much of it from western European countries: the UK (Clayton et al., 1997; Smith et al.,
1997), The Netherlands (Velthof et al., 1996; Bussink and Oenema, 1997), and France
(Hénault et al. 1998a,b). Harrison and Webb (2001) concluded that higher emissions can
occur under some circumstances, and they proposed a scheme for assessing the relative
emissions of N2O from different fertilisers (Table 1).
Table 1. Proposed scheme for assessing the relative emissions of N 2O from different
fertilisers (after Harrison and Webb, 2001).
Soil
moisture
Dry
Wet
Very wet
Relative emission from
nitrate and ammonium
N
low nitrate 
ammonium
high nitrate >
ammonium
Relative
emission from
urea
urea 
ammonium
urea >>
ammonium
high
urea 
ammonium
nitrate >>
ammonium
Comments
Rate of urea
hydrolysis limited
Rate of urea
hydrolysis
increases with
temperature
High pH associated
with hydrolysis
dispersed by
moisture
More recent data from the UK have also demonstrated the potential for high emissions from
nitrate-containing fertilisers when soils are wet. In the study prior to this one, NT2603
(Dampney et al., 2004), by far the highest EF, both for a single application of N (11%) and
for the total annual input (3.9%), took place after the use of CAN, and it was shown that the
emissions increased exponentially with soil water-filled pore space (WFPS). Published
studies in the UK have shown emissions from AN of up to 6.5% (Dobbie and Smith, 2003a),
also with the highest values from grassland increasing exponentially with WFPS. These
latter studies have also shown that the variability of rainfall around the time of N application
can give rise to variations in annual emissions of up to 20-fold.
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Nitrification inhibitors, slow- and controlled-release fertilisers
Dobbie and Smith (2003b) showed that on grassland in Scotland over a 2-year period, the
emission from a combination of urea and the nitrification inhibitor DCD (dicyandiamide) was
only half that from unmodified urea, which itself was substantially less than from AN. Similar
results have been reported from The Netherlands (Velthof et al., 1996) and New Zealand (Di
and Cameron, 2002). In continental Europe, the nitrification inhibitor 3,4-dimethylpyrazole
phosphate (DMPP; trade name ENTEC) has been shown by Weiske et al. (2001) to reduce
emissions by an average of 49% compared with 26% under the same conditions for DCD.
Slow- and controlled-release fertilisers have also been shown to reduce leaching and
gaseous losses of N from agricultural systems to the environment (e.g. Mikkelsen et al.,
1994). There have been fewer research studies on their impact on N 2O mitigation, compared
with those of nitrification inhibitors, but the results are fairly comparable with those obtained
with the latter products. Mosier (2002) showed a two-thirds reduction in N2O emissions from
a maize crop in the USA using controlled-release urea as compared with unmodified urea.
The reduction in net fertiliser-related emissions from barley (i.e. after subtracting those from
the unfertilised control), was of the order of 50%. Dobbie and Smith (2003b) found a
reduction in emissions of about one third using controlled release urea, compared with those
from unmodified urea, from silage grass in Scotland; this compared with a 50% reduction
when DCD-modified urea was used. The reduced effectiveness of the controlled-release
form in this environment appeared to be due to some of the release of mineral N taking place
very late in the season, when the demand of the grass for nutrients was in decline.
Indirect emissions of N2O
The most reliable estimate of indirect N2O emissions involves the use of well-established
emission factors where they exist, and default values where they do not. Thus emissions of
ammonia, at c.25% of N applied, are c.10 times greater following the application of urea than
following the application of AN (2-3% of N applied) (NT2605 WP1b, Chadwick et al., 2005),
whereas for the purposes of calculating indirect N2O emissions the IPCC default value is
10% ammonia loss, regardless of fertiliser form (IPCC, 1997; Mosier et al., 1998). However,
the IPCC default factor for indirect emissions of N2O following re-deposition of volatilised
ammonia is the only one available, and is set at 1.0% of the ammonia-N (IPCC, 1997;
Mosier et al., 1998). Thus the effective EFs for ‘indirect’ emissions of N 2O following
volatilisation of applied fertiliser N, based on NT26 data and this latter IPCC default factor,
are 0.25% and 0.025% of the N applied as urea and AN, respectively, and these need to be
added to the EFs for direct emissions of N2O for those fertilisers in any comparison of their
impacts on total emissions of N2O.
For assessment of indirect emissions following nitrate leaching in drainage waters to
aquifers, surface waters and sediments, the default leaching factor is 30%, and the IPCC
default EF for N2O is 2.5% of this leached N fraction (IPCC, 1997; Mosier et al., 1998). This
factor is now expected (K.A. Smith, pers. comm.) to be revised downwards to 1.25%, based
on new data (e.g. Reay et al., 2004, 2005; Sawamoto et al. 2005; Clough et al., (in press,
2006). Macdonald et al. (2006, NT2605 WP4) showed no consistent differences in total N
leaching between AN and urea fertilisers (after taking into account ammonia volatilisation
losses to air from urea). Thus, additional adjustments to the EF for indirect N 2O emissions
following leaching, comparable with those made above for N volatilisation/deposition, should
not need to be made to take account of different fertiliser forms.
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2.3.2 Modelling
Modelling has potential for identifying likely high-emission situations, and thus helping to
focus attention on where mitigation efforts are best made. Research is in progress on both
simple empirical and complex mechanistic models which predict N 2O emission from
agricultural systems. The DeNitrification-DeComposition (DNDC) model (Li et al., 1992a,b)
and the Daycent modification of the Century model (Del Grosso et al., 2000) are perhaps the
best known and most widely used. The former has been used to produce estimates of the
national total emission, and regional variations, in the USA and China, and has been
adapted for local conditions to make it more usable in, for example, the UK (Brown et al.,
2002), and New Zealand (Saggar et al., 2004). The model has the potential to evaluate
mitigation options, as well as to estimate fluxes under existing management. In other UK
approaches to modelling and upscaling to regional and national levels, Sozanska et al.
(2002) developed a spatial inventory of N2O emissions as a function of N input, water-filled
pore space, soil temperature and land use, and Lilly et al. (2003) modelled emissions from
two regions of Scotland on the basis of crop growth cycles, soil wetness and fertiliser
applications. More recently a spreadsheet model of total N 2O emissions from Scottish
agricultural soils has estimated N inputs on a 2 km grid square basis, using EFs that are
adjusted for rainfall (SEERAD, 2004; Flynn et al., 2005). A hybrid part-empirical, part
process-based model has also been developed to predict emissions from grassland soils
(SEERAD, 2004).
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3. Experimental design, treatments and methodology
Nitrous oxide flux measurements were made at two grassland sites and one arable site in
2004: IGER Rowden (grass), SAC Crichton, Dumfries (grass) and ADAS Terrington (winter
wheat). In 2005 the measurements were made at one grass and two arable sites: IGER De
Bathe (grass), SAC Bush, Edinburgh (winter wheat) and ADAS Boxworth (winter wheat). Site
details are given in Appendix 1. Measurements were made on the same plots that were used
for crop response assessments (NT2605 WP1a, Dampney et al., 2006).
3.1 Fertiliser forms
Nitrous oxide emissions were measured following the application of 5 different fertiliser N
products at 6 sites during 2004 and 2005. Nitrous oxide emissions were also measured from
a nil-N control treatment at each site
In 2004, each grassland experiment tested 5 fertiliser N products, viz:
(i)
ammonium nitrate - AN
(ii)
urea - U
(iii)
urea + Agrotain rate 1 (500 mg/kg active ingredient nBTPT / kg of urea) coated –
U+Ag500c
(iv)
U+Ag1000c
(v)
urea ammonium sulphate – UAS.
In 2004, the winter cereal experiment tested 5 fertiliser N treatments, viz:
(i)
(ii)
urea - U
(iii)
urea + Agrotain (1000 mg/kg active ingredient nBTPT / kg of urea) coated –
U+Ag1000c
(iv)
urea ammonium nitrate - UAN
(v)
urea ammonium nitrate + Agrotain (1000 mg/kg active ingredient nBTPT / kg of urea) –
UAN+Ag1000.
In 2004, only urea coated with Agrotain was available for testing. Agrotain product (25%
nBTPT active ingredient) was coated to granular urea at rates of 500 mg nBTPT/kg urea
(U+Ag500c) and 1000 mg nBTPT/kg urea (U+Ag1000c), using a high velocity centrifugal
seed dressing machine. Laboratory tests of nBTPT confirmed that a very even coating was
obtained. These coated urea materials were centrally prepared at ADAS Boxworth at
intervals during the season, and used at each experimental site within 2 weeks of
preparation. The content of nBTPT in each batch was confirmed by Queens University
Belfast using HPLC analysis.
In 2005, urea with Agrotain added to the urea melt was available for testing. This material
was specially produced by addition of Agrotain to the hot urea melt before the granulation
process. This method of addition means that the Agrotain is evenly mixed within each urea
granule rather than as an external coating. Material with 2 rates of Agrotain addition were
tested – 250 mg nBTPT/kg urea (U+Ag250m) and 500 mg nBTPT/kg urea (U+Ag500m). The
materials were specially prepared using a pilot granulation plant. The content of nBTPT was
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confirmed on receipt, and then monitored through the application season by Queens
University Belfast using HPLC analysis. Additionally in 2005, urea coated with Agrotain was
also used as in 2004, but at 500 mg nBTPT/kg urea (U+Ag500c).
In 2005, the grassland experiment tested 5 fertiliser N products, viz:
(i)
(ii)
urea - U
(iii)
urea + Agrotain rate 1 (250 mg/kg active ingredient nBTPT / kg of urea) in the melt –
U+Ag250m
(iv)
urea + Agrotain rate 2 (500 mg/kg active ingredient nBTPT / kg of urea) in the melt –
U+Ag500m
(v)
U+Ag500c.
In 2005, each winter cereal experiment tested 5 fertiliser nitrogen treatments, viz:
(i)
(ii)
urea - U
(iii)
urea + Agrotain (500 mg/kg active ingredient nBTPT / kg of urea) in the melt –
U+Ag500m
(iv)
urea ammonium nitrate - UAN
(v)
urea ammonium nitrate + Agrotain (500 mg/kg active ingredient nBTPT / kg of urea) –
UAN+Ag500
Measurements of N2O flux and associated soil analyses were made only on the plots
fertilised at the RB209 recommended N rates and fertilised at times of the year typical of N
fertiliser applications (Appendix 2).
3.2 Nitrous oxide emission measurements
All measurements were made by the closed static chamber method (e.g. Smith et al., 1995),
using chambers 40 x 40 cm. Two chambers were located on each of three replicate plots of
each N treatment at each site, totalling six chambers per treatment per site.
Chambers were embedded to a few centimetres into the soil, and were gas-tight when
closed so that the accumulated N2O emissions from the area of soil surface encompassed
by the chamber were contained within the chamber. Sampling generally took place just
before N fertiliser application, then daily for several days, then at 2-day, 3-day and eventually
weekly intervals as fluxes returned to control levels. On each sampling date, the time of
closing each chamber and the time of taking the gas sample (just prior to opening the
chamber) were recorded and the closure interval calculated. Gas samples were taken from
the chambers at the end of the closure period. On a few occasions, samples were also taken
from randomly selected chambers at intervals of 10 or 15 min after closure, to determine the
linearity of concentration increase with time. All gas samples taken from the chambers were
transferred to the laboratory in gas-tight containers, and analysed by gas chromatography
(GC) using electron-capture detectors. The GC response was calibrated using certified N2O
standard gas mixtures.
3.3 Other measurements
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On each gas sampling occasion, soil temperature was measured. On some or all sampling
dates (depending on site), topsoil samples were taken using augers. Subsamples of topsoil
were dried and weighed and the gravimetric water content determined. Additional
subsamples were extracted and analysed for nitrate and ammonium by standard colorimetric
methods. Soil bulk density was determined, and the results used to convert gravimetric water
contents to water-filled pore space (WFPS).
3.4 Data manipulation
Mean N2O emissions were determined for each day of measurement for each fertiliser-N
material and also for the unfertilised control, and integrated over time by linear interpolation
and trapezoidal calculation. Emissions from the control treatment were subtracted from the
corresponding values for fertilised plots, giving net emissions attributable to the fertiliser N
applied. For each application period and for the whole season, EFs were calculated as the
percentage of the applied fertiliser-N that was released as N2O-N. Hence these EFs only
account for direct N2O emissions.
All mean emission data were plotted against time, to show the dynamics of the emissions.
The trends of the cumulative emissions were plotted, as were the fluctuations in the soil
temperature, WFPS, and ammonium-N and nitrate-N concentrations.
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4. Results
All N2O flux measurements were carried out on the RB209 recommended N rate plots (see
section 3.1 and Appendix 2). In the experiments started in spring 2004, measurements
covered the periods between successive fertilisations and from the final fertilisation until
26.01.05 and 09.02.05 for the Crichton and Rowden sites, respectively, and until 02.03.05 at
Terrington. The experiments started in spring 2005 again covered the periods between N
applications, and then from the final application until the termination of sampling (at De
Bathe on 02.09.05; at Bush on 29.08.05; and at Boxworth on 21.09.05).
The dynamics of N2O emissions following each N application and complementary
measurements of soil temperature, WFPS, and ammonium-N and nitrate-N concentrations
are shown in Appendix 3.
4.1 Emissions following 1st fertiliser-N applications, March 2004

At Rowden (grassland), where there was a humose topsoil, only AN gave a substantial
emission peak after N application, with values up to c.70 g N2O-N ha-1 day-1.

Total emissions, up to the next application, were greater for AN (0.42 kg N 2O-N ha-1) than
for urea (0.23 kg N2O-N ha-1) or UAS (0.16 kg N2O-N ha-1). Emissions from U+Ag500c
and U+Ag1000c were 0.12 and 0.09 kg N2O-N ha-1, respectively (Table 2). These values
corresponded to net EFs (having subtracted the mean emission from the control plots) of
only 0.02-0.84% (Table 3), which were small compared with the IPCC default value of
1.25%, though this value relates to a full year’s emission as discussed below. Soil
temperatures were low (3-6C) and WFPS values were in the range 70->80%.

At Crichton, on a mineral soil and also under grass, the highest daily emissions were also
up to about 70 g N2O-N ha-1 day-1, and came from the AN treatment. U+Ag500c and UAS
gave the next largest emission peaks, but at only about half the size. As at Rowden, the
largest emission was from AN (0.50 kg N2O-N ha-1), while those for urea, U+Ag500c,
U+Ag1000c and UAS were similar, at 0.19-0.26 kg N2O-N ha-1 (Table 2). The
corresponding net EFs were 0.23-1.02% (Table 3), i.e. ranging from c.20% to 80% of the
IPCC default factor. Soil temperatures were also low here (<5C), and WFPS values were
60-70%.

At Terrington, the only arable (winter wheat) site in 2004, the highest daily emission
following the first N application was only about 30 g N 2O-N ha-1 day-1. The total up to the
next N application ranged from 0.14 kg N2O-N ha-1 (urea) to 0.22 kg (AN), with the other
treatments within this range (Table 2). The corresponding net EFs ranged from 0.15%
(urea) to 0.34% (AN) (Table 3). Soil temperatures after fertilisation fluctuated more at this
site, but were mostly <6C, and WFPS values were consistently around 60%.
4.2 Emissions following 2nd fertiliser-N application, 2004

At Rowden (grassland) after the 2nd N application, the fluxes were higher than those after
the first application, and showed a much greater variation between fertiliser types. The
peak for AN was by far the highest, exceeding 300 g N 2O-N ha-1 day-1 on one occasion.
Over the period up to the next N application, emissions were greater from AN (1.68 kg
14
________________________________________________________________________________
N2O-N ha-1) than from urea (0.76 kg N2O-N ha-1) or from UAS (0.32 kg N2O-N ha-1). The
addition of Agrotain to urea (U+Ag500c, U+Ag1000c) reduced emissions to 0.45 and 0.23
kg N2O-N ha-1, respectively. (Table 2). The corresponding net EFs ranged from 0.06% for
U+Ag1000c to 1.88% for AN (Table 3). The soil was warmer (8-10C) and wetter (c.90%
WFPS) when the N was applied than at the time of the first N application.

At Crichton (grassland), compared with the Rowden site the emissions changed much
less from those observed after the previous application. The AN and U+Ag1000c gave
similar peaks to those observed after the first application, while the peaks for unmodified
urea, U+Ag500c and UAS were slightly higher than before. U+Ag1000c again gave the
lowest value up to the next N application, 0.28 kg N2O-N ha-1, and AN gave 0.58 kg N2ON ha-1. The main change from the previous period was that U+Ag500c gave the highest
flux: 0.83 kg N2O-N ha-1 (Table 2). The net EFs ranged from 0.22% (U+Ag1000c) to
0.91% (U+Ag500c) (Table 3). At Crichton, as at Rowden, the soil had warmed to 8-10C,
and again like the Rowden site the soil was somewhat wetter (70-75% WFPS) than at the
time of the first application of N.

At Terrington (winter wheat), somewhat larger emission maxima were found than after the
first N application, but the highest emissions were still only about 60 g N 2O-N ha-1 day-1
(for AN and for U+Ag1000c). The total emissions from the UAN forms up to the next N
application were little changed from those for the previous period, but those from modified
and unmodified urea and from AN all increased substantially (Table 2). The corresponding
net EFs ranged from 0.14% for UAN+Ag1000 to 0.54% for urea (Table 3). Soil
temperatures at and after N application were very similar to those at the other sites, but
the WFPS values had decreased very slightly to c.55-60%.
4.3 Emissions following 3rd and 4th fertiliser-N applications, 2004

At Rowden (grassland), substantial peak fluxes were seen from all the N forms, following
the 3rd N application. The maximum values ranged from c.70 N2O-N ha-1 day-1 only for
U+Ag1000c to c.180 N2O-N ha-1 day-1 for AN. The environmental conditions were
substantially different from those at the two previous fertilisations, with the soil
temperature at about 15C, and the WFPS value having fallen from near-saturation to
c.70% when the N was applied. For the 3rd time in succession the lowest total N2O
emissions were from the plots receiving U+Ag1000c (1.06 kg N2O-N ha-1) and the highest
were from those receiving AN (2.34 kg N2O-N ha-1) (Table 2). The corresponding net EFs
were 0.82-2.1% (Table 3).

At Rowden only, there was a 4th application of N in July, when the soil was c.17-18C, but
the WFPS only at 40-50%. Emissions immediately after N application were low for all
forms of N, but as measurement of N2O emissions continued through the autumn there
were wetter periods when fluxes were at substantially higher levels than those from the
unfertilised control plot. Over the period until measurements ceased on 9 th February 2005,
the lowest emissions were for U+Ag500c and U+Ag1000c, at 2.43 and 2.55 kg N 2O-N ha1, respectively, whereas urea gave the greatest emission of 4.8 kg N O-N ha-1, with UAS
2
and AN intermediate, at 3.9 and 3.7 kg N2O-N ha-1 (Table 2). The net EFs for the
measurement period ranged from 1.2% (U+Ag500c) to 4.2% (urea) (Table 3).

At Crichton (grassland), small peaks with maxima of 20-50 g N2O-N ha-1 day-1 were
observed after the 3rd N application. As this was the last application at this site, and N 2O
15
________________________________________________________________________________
emissions were measured until 26th January 2005, the totals are not directly comparable
with those from the 3rd application at Rowden. Through the autumn, emissions from
fertilised plots continued to be generally well above those from the control. Total
emissions for the period ranged from 1.27 kg N2O-N ha-1 (urea) to 1.64 kg N2O-N ha-1
(U+Ag500c) (Table 2), with net EFs of 0.61-0.99% (Table 3). Soil temperatures were c.15
C, and WFPS values were 55-60%, following N application.

At Terrington (winter wheat), all forms of N gave significant emission peaks after the 3rd N
application, ranging from c.100 g N2O-N ha-1 day-1 for U+Ag1000c, to c.240 g N2O-N ha-1
day-1 for UAN. Soil temperatures were c.12 C when the N was applied, and then
increased, while the WFPS was briefly at its highest at c.65%. The total emissions until
2nd March 2005 ranged from 1.78 kg N2O-N ha-1 for UAN+Ag1000 to 2.69 kg N2O-N ha-1
for UAN. However, the emissions of N2O from the control plots was much higher than at
the other two sites (1.4 kg N2O-N ha-1 until the end of sampling; Table 2), and so the net
EFs following this 3rd application were correspondingly reduced, ranging from 0.42% for
UAN+Ag1000 to 1.43% for UAN (Table 3).
4.4 Emissions and EFs for the whole 2004 season

At the Rowden grassland site there were no significant differences in emissions between
treatments. Total net N2O emission from AN and urea were 6.21 and 5.92 kg N2O-N ha-1,
respectively. The modified urea gave only about one-third as much; 1.97 kg N2O-N ha-1
from U+Ag1000c and 2.42 kg N2O-N ha-1 from U+Ag500c. The emission for UAS fell
between these values (Table 2). The net EF for urea and AN were very similar at 1.97 and
2.07%, respectively. The net EF for modified urea was 0.65 and 0.81% for U+Ag1000c
and U+Ag500c, respectively, while the EF for UAS was in the middle of the range, at
1.30% (Table 3).

At the other grassland site, Crichton, total net seasonal emissions were much less than at
Rowden. The smallest emission was from U+Ag1000c, at 0.92 kg N 2O-N ha-1, but the
largest was from U+Ag500c, at 1.87 kg N2O-N ha-1 (Table 2). The corresponding net EF
values were 0.42% and 0.85%. Again the differences between N forms were not
significant (Table 3).

At the arable site, Terrington, none of the differences between the five fertiliser forms were
statistically significant. The values for total net emissions ranged from 0.58 kg N 2O-N ha-1
(UAN+Ag1000) to 1.54 kg N2O-N ha-1 (UAN). The value for AN fell in the middle of the
range, at 1.00 kg N2O-N ha-1 (Table 2). The corresponding net EFs ranged between
0.27% and 0.70% (Table 3).
4.5 Emissions following 1st fertiliser-N applications, February/March 2005

At De Bathe, which was grassland on a mineral soil, N2O fluxes were exceedingly low – a
maximum of between 10 and 20 g N2O-N ha-1 day-1 for AN, and <10 g N2O-N ha-1 day-1
for all other N forms. The N application was made when the soil was at only 3C and had
WFPS values of c.60%. The total N2O emission from the plots receiving AN, for the period
up to the next N application, was 0.18 kg N2O-N ha-1, while that from the other N forms
ranged from only 0.05 to 0.07 kg N2O-N ha-1 (Table 2). The net EFs were 0.06-0.12% for
the various forms of urea, while that for AN was 0.39% (Table 3).
16
________________________________________________________________________________

Equally low peak emissions were observed at the arable (winter wheat) site at Bush – with
maxima of only 10-20 g N2O-N ha-1 day-1. The conditions under which the N was applied
were soil temperatures of 3C and WFPS values of 70-75%. The total emissions for the
period up to the 2nd N application were, however, above those at the De Bathe site, at
between 0.16 kg N2O-N ha-1 (UAN) and 0.24 kg N2O-N ha-1 (urea) (Table 2). The
corresponding net EFs ranged from 0.30 to 0.49% (Table 3).

At Boxworth, also sown to winter wheat, the soil was at 5C and c.55% WFPS when the
first N application was made. Under these conditions, N2O emissions were low; only two
flux values exceeding 10 g N2O-N ha-1 day-1 were recorded (for AN and urea), and total
emissions up to the 2nd N application ranged from only 0.04 kg N 2O-N ha-1 for
UAN+Ag500 to 0.06 kg N2O-N ha-1 for urea (Table 2). The net EFs were 0.08-0.23%
(Table 3).
4.6 Emissions following 2nd fertiliser-N applications, 2005

At De Bathe (grassland), the 2nd N application was the final one, and took place when the
soil temperature was 10-12C and the WFPS at c.65%. A peak flux of >100 g N2O-N ha-1
day-1 was observed from the AN treatment, but maximum emissions from all the other N
forms were much less. The total emission from AN plots over the period was 0.76 kg N 2ON ha-1, whereas the next highest was 0.09 kg N2O-N ha-1 (Table 2).

At Bush (winter wheat), substantial fluxes were observed after fertilisation from all the
forms containing AN, with peaks of between 50 and 100 g N 2O-N ha-1 day-1 for AN and
about 50 g N2O-N ha-1 day-1 for UAN with and without Agrotain. No such peaks were
observed for the urea-containing fertiliser forms. The soil WFPS was close to 70% at this
time, and soil temperatures were still low (c.6C). Total emissions up to the 3rd N
application ranged from 0.34 kg N2O-N ha-1 for urea to 0.98 kg N2O-N ha-1 for AN (Table
2). The corresponding net EFs were 0.30-1.01% (Table 3).

At Boxworth, also under winter wheat, maximum fluxes reached around 40 g N 2O-N ha-1
day-1 for all N forms except AN, for which the maximum was no more than 10 g N2O-N
ha-1 day-1. The soil was at 8-9C and 50-55% WFPS when the N was applied. Total
emissions up the next N application were small: ranging from 0.11 kg N 2O-N ha-1 (AN) to
0.32 kg N2O-N ha-1 (UAN) (Table 2). The corresponding net EFs were 0.11-0.46% (Table
3).
4.7 Emissions following 3rd fertiliser-N applications 2005

At Bush (winter wheat), the 3rd application of N was followed a few days later by much
larger emission peaks than seen previously, all of which were of the same order (maxima
of c.150-230 g N2O-N ha-1 day-1). The soil was at c.10 C but only at c.50% WFPS when
the N was applied, but rainfall raised the WFPS values to >60%, after which these
emission peaks occurred. Total emissions up to the end of sampling ranged from 1.69 kg
N2O-N ha-1 for UAN+Ag500 to 2.82 kg N2O-N ha-1 for AN (Table 2). The corresponding
net EFs were 1.75-2.99%.

At Boxworth (winter wheat), the final N application was followed immediately by only small
emission peaks (<20 g N2O-N ha-1). At this time the soil was at 10-12C but only at c. 50%
WFPS, and continued to dry out thereafter. Larger peaks were observed from most of the
17
________________________________________________________________________________
N forms later on, in July, after a partial rewetting of the soil and in warmer conditions. The
total emissions to the end of the sampling period ranged from 0.70 kg N2O-N ha-1
(UAN+500Ag) to 1.13 kg (urea) (Table 2). The corresponding net EFs were 0.37-1.08%
(Table 3).
4.8 Emissions and EFs for the whole 2005 study period

At De Bathe (grassland) the net total emission from AN, at 1.07 kg N2O-N ha-1, was
significantly greater (P<0.05) than from the other fertiliser forms, from which the net
seasonal emissions were very small, ranging from 0.15 kg N2O-N ha-1 for urea to 0.29 kg
N2O-N ha-1 for U+Ag500Agc (Table 2). The corresponding values for the net EFs were
between 0.12% and 0.24% for the forms containing urea, and 0.87% for AN (Table 3).

At Bush (winter wheat) emissions from AN were significantly (P<0.05) greater than from
UAN+Ag500. Urea and UAN forms gave net total emissions within a fairly narrow range of
2.19 to 2.90 kg N2O-N ha-1, whereas the emission from AN was 3.79 kg N2O-N ha-1 (Table
2). The corresponding net EFs were 1.72% for AN, and between 1.0 and 1.32% for the
other forms (Table 3).

At Boxworth (winter wheat) there were no significant differences in emissions (P>0.05)
between treatments. Total net emissions were lowest for AN (0.37 kg N 2O-N ha-1), in
contrast with the other sites. The corresponding values for the other N forms ranged from
0.52 kg N2O-N ha-1 for UAN+Ag500 to 0.97 kg N2O-N ha-1 for urea (Table 2). The net EFs
ranged from 0.23% for AN to 0.60% for urea (Table 3).
18
________________________________________________________________________________
Table 2. N2O emissions following each fertiliser N application, and total seasonal emissions,
for three grassland sites and three winter wheat sites in 2004 and 2005.
Site/Crop/Yr
N2O emission after each fertiliser application (kg N ha-1)
N material
N1
N2
N3
N4
Total
Net total (fert –
control)
Rowden
(2004)
(Grass)
AN
Urea
U+Ag1000c
U+Ag500c
UAS
Control
0.42
0.23
0.09
0.12
0.16
0.08
1.68
0.76
0.23
0.45
0.32
0.18
2.34
2.09
1.06
1.38
1.47
0.24
3.73
4.80
2.55
2.43
3.93
1.46
8.17 ± 1.84a
7.88 ± 3.97a
3.93 ± 0.38a
4.38 ± 0.74a
5.88 ± 1.71a
1.96 ± 0.56a
6.21 ± 1.92a
5.92 ± 4.01a
1.97 ± 0.67a
2.42 ± 0.92a
3.92 ± 1.80a
Crichton
(2004)
(Grass)
AN
Urea
U+Ag1000c
U+Ag500c
UAS
Control
0.50
0.22
0.19
0.26
0.24
0.10
0.58
0.39
0.28
0.83
0.52
0.10
1.49
1.27
1.31
1.64
1.28
0.66
N/A
N/A
N/A
N/A
N/A
N/A
2.57 ± 0.65b
1.88 ± 0.60ab
1.78 ± 0.46ab
2.73 ± 0.88b
2.04 ± 0.53ab
0.86 ± 0.24a
1.71 ± 0.69a
1.02 ± 0.65a
0.92 ± 0.52a
1.87 ± 0.91a
1.18 ± 0.58a
Terrington
(2004)
(W. wheat)
AN
Urea
U+Ag1000c
UAN
UAN+Ag1000
Control
0.22
0.14
0.19
0.20
0.16
0.08
0.32
0.52
0.47
0.17
0.17
0.04
1.98
2.33
2.37
2.69
1.78
1.40
N/A
N/A
N/A
N/A
N/A
N/A
2.52 ± 0.13ab
2.99 ± 0.07b
3.03 ± 0.47b
3.06 ± 0.08b
2.11 ± 0.33ab
1.52 ± 0.15a
1.00 ± 0.20a
1.47 ± 0.17a
1.49 ± 0.49a
1.54 ± 0.17a
0.58 ± 0.36a
De Bathe
(2005)
(Grass)
AN
Urea
U+Ag500c
U+Ag500m
U+Ag250m
Control
0.18
0.05
0.07
0.05
0.07
0.02
0.76
-0.03
0.09
0.02
0.02
-0.15
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
0.94 ± 0.30b
0.02 ± 0.02a
0.16 ± 0.04a
0.07 ± 0.01a
0.09 ± 0.01a
-0.13 ± 0.01a
1.07 ± 0.30b
0.15 ± 0.02a
0.29 ± 0.04a
0.20 ± 0.01a
0.22 ± 0.01a
Bush
(2005)
(W. wheat)
AN
Urea
U+Ag500m
UAN
UAN+Ag500
Control
0.22
0.24
0.21
0.16
0.20
0.04
0.98
0.34
0.36
0.53
0.53
0.07
2.82
2.58
2.22
2.16
1.69
0.12
N/A
N/A
N/A
N/A
N/A
N/A
4.02 ± 0.94b
3.16 ± 0.65bc
2.79 ± 0.48bc
2.85 ± 0.67bc
2.42± 0.51c
0.23 ± 0.11a
3.79 ± 0.95a
2.90 ± 0.66ab
2.56 ± 0.49ab
2.62 ± 0.68ab
2.19 ± 0.52b
Boxworth
(2005)
(W. wheat)
AN
Urea
U+Ag500m
UAN
UAN+Ag500
Control
0.04
0.06
0.05
0.01
0.00
-0.03
0.11
0.27
0.28
0.32
0.31
0.04
0.71
1.13
0.95
0.78
0.70
0.48
N/A
N/A
N/A
N/A
N/A
N/A
0.86 ± 0.29a
1.46 ± 0.31a
1.28 ± 0.38a
1.11 ± 0.35a
1.01 ± 0.13a
0.49 ± 0.09a
0.37 ± 0.30a
0.97 ± 0.32a
0.79 ± 0.39a
0.62 ± 0.36a
0.52 ± 0.16a
Values in columns with different letters significantly different (P<0.05). N/A: not applicable.
19
________________________________________________________________________________
Table 3. N2O emission factors for each type of fertiliser N and each application period, and
seasonal weighted mean EFs, for three grassland and three winter wheat sites in 2004 and
2005. IPCC default emission factor = 1.25 ± 1.0%.
Site/Crop/
Year
N material
Net N2O emission factor (%)
N1
N2
N3
N4
Seasonal
mean
Rowden
(2004)
(Grass)
AN
Urea
U+Ag1000c
U+Ag500c
UAS
0.84
0.37
0.02
0.11
0.19
1.88
0.73
0.06
0.33
0.17
2.10
1.84
0.82
1.14
1.22
2.83
4.18
1.36
1.21
3.09
2.07 ± 0.64a
1.97 ± 1.34a
0.65 ± 0.22a
0.81 ± 0.31a
1.30 ± 0.60a
Crichton
(2004)
(Grass)
AN
Urea
U+Ag1000c
U+Ag500c
UAS
1.02
0.31
0.23
0.40
0.36
0.60
0.36
0.22
0.91
0.53
0.84
0.61
0.65
0.99
0.62
N/A
N/A
N/A
N/A
N/A
0.78 ± 0.31a
0.47 ± 0.29a
0.42 ± 0.23a
0.85 ± 0.41a
0.54 ± 0.26a
Terrington
(2004)
(W. wheat)
AN
Urea
U+Ag1000c
UAN
UAN+Ag1000
0.34
0.15
0.26
0.30
0.20
0.31
0.54
0.47
0.15
0.14
0.65
1.03
1.07
1.43
0.42
N/A
N/A
N/A
N/A
N/A
0.45 ± 0.09a
0.67 ± 0.08a
0.68 ± 0.22a
0.70 ± 0.08a
0.27 ± 0.16a
De Bathe
(2005)
(Grass)
AN
Urea
U+Ag500c
U+Ag500m
U+Ag250m
0.39
0.07
0.12
0.06
0.12
1.13
0.15
0.29
0.21
0.20
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
0.87 ± 0.25a
0.12 ± 0.02b
0.24 ± 0.03b
0.16 ± 0.01b
0.17 ± 0.01b
Bush
(2005)
(W. wheat)
AN
Urea
U+Ag500m
UAN
UAN+Ag500
0.45
0.49
0.41
0.30
0.40
1.01
0.30
0.33
0.52
0.51
2.99
2.73
2.33
2.27
1.75
N/A
N/A
N/A
N/A
N/A
1.72 ± 0.43a
1.32 ± 0.30ab
1.16 ± 0.22ab
1.19 ± 0.31ab
1.00 ± 0.24b
Boxworth
(2005)
(W. wheat)
AN
Urea
U+Ag500m
UAN
UAN+Ag500
0.17
0.23
0.18
0.10
0.08
0.11
0.38
0.41
0.46
0.44
0.38
1.08
0.78
0.50
0.37
N/A
N/A
N/A
N/A
N/A
0.23 ± 0.19a
0.60 ± 0.20a
0.49 ± 0.25a
0.39 ± 0.22a
0.33 ± 0.10a
Values in columns with different letters are significantly different (P<0.05).
20
________________________________________________________________________________
4.9 General relationships between emissions from different N forms

All the net EFs obtained for all fertiliser forms except unmodified urea, in both study years,
that are contained in Table 3 are plotted against the corresponding values for urea in Fig.
1. In the two years of the NT2605 programme there was little by way of large emission
events, and the highest annual EFs were around 2%, for both AN and urea. The EFs for
the various N forms generally increased as the EF for urea increased, but there is some
indication of above-trend values for N2O emission from AN, and a reduction below the
trend where the urea had been modified by the addition of Agrotain, at the highest flux
level for urea. In Fig. 2, the corresponding data from the NT2603 study have been added,
and the only additional point to note is the very high seasonal emission for CAN recorded
in 2003 for the Hillsborough site in N. Ireland.

The impact of adding Agrotain to urea is illustrated in Figs. 3 and 4, using data for the 3
years 2003-2005 (NT2603 and NT2605 studies). In the Fig. 3, the EFs for the different
rates of Agrotain addition are plotted separately; while in Fig. 4 all the data are pooled and
an overall regression calculated. There is some indication that the addition of Agrotain
results in reduced emissions.

A similar exercise was carried out to compare the effect on emissions of using an N form
containing nitrate with the effect of using ordinary urea. Fig. 5 shows the EFs for AN and
CAN, over the 3 years, plotted separately against the EFs for urea, while all the AN/CAN
data were pooled in Fig. 6, and the regression calculated. The regression suggests
moderately greater direct emissions from the nitrate forms than from urea, but they are not
significantly different from the 1:1 line, and do not take into account the associated indirect
emissions; this aspect is considered in the section 5 below. With regard to possible
differences between AN and CAN, in terms of N2O emissions, no AN was used at
Hillsborough, but at those sites where CAN and AN were directly compared in 2003, the
ratio of CAN to AN ranged from about 0.5 to nearly 2, showing that CAN does not
consistently give a higher emission than that from AN.
21
________________________________________________________________________________
3.5
EF for other N forms (%)
3.0
2.5
2.0
Ammonium nitrate
U + Ag1000
U + Ag500 or 250
UAS
UAN
UAN + Ag1000
UAN + Ag500
1:1 line
1.5
1.0
0.5
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
EF for Urea (%)
Figure 1
N2O whole-season emission factors for different forms of N fertiliser vs.
corresponding EFs for unmodified urea. Data for all sites in 2004 and 2005.
5
EF for other N forms (%)
4
3
2
Ammonium nitrate
U + Ag1000
U + Ag500 or 250
UAS
UAN
UAN + Ag1000
UAN + Ag500
CAN
1:1 line
1
0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
EF for Urea (%)
Figure 2.
N2O whole-season emission factors for different forms of N fertiliser vs.
corresponding EFs for unmodified urea. Data for all sites, 2003-2005.
22
________________________________________________________________________________
3.0
EF for U + Ag mixtures (%)
2.5
U + Ag1000
U + Ag500 or 250
1:1 line
2.0
1.5
1.0
0.5
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
EF for Urea (%)
Figure 3.
N2O whole-season emission factors for urea containing different concentrations
of Agrotain vs. corresponding EFs for unmodified urea. Data for all sites, 20032005.
3.5
EF (U+Ag, all) vs Urea
Y = 0.46X + 0.25
1:1 line
EF for U + Ag, all mixtures (%)
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.0
0.5
1.0
1.5
2.0
2.5
EF for urea (%)
Figure 4.
N2O whole-season emission factors for urea containing any concentration of
Agrotain vs. corresponding EFs for unmodified urea, and regression line. Data
for all sites, 2003-2005.
23
________________________________________________________________________________
5
EF for AN, CAN (%)
4
Ammonium nitrate
CAN
1:1 line
3
2
1
0
-1
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
EF for Urea (%)
Figure 5.
N2O whole-season emission factors for N fertilisers containing nitrate, vs.
corresponding EFs for unmodified urea. Data for all sites, 2003-2005.
5
All AN and CAN
Y = 1.34X - 0.006
1:1 line
EF for AN, CAN (%)
4
3
2
1
0
0
1
2
3
EF for urea (%)
Figure 6.
N2O whole-season emission factors for N fertilisers containing nitrate in any
form, vs. corresponding EFs for unmodified urea, and regression line. Data for
all sites, 2003-2005.
24
________________________________________________________________________________
5. Discussion
5.1 Importance of environmental conditions and N form
When soil conditions are very dry, or cold (i.e. <5C), or both, the observed N2O fluxes in the
NT26 programme and elsewhere have always been very low, irrespective of the form of
fertiliser N applied. Conversely, when the soils are much wetter (i.e. WFPS >70-80%) and
warmer, fluxes can be very high. These high fluxes take place predominantly during
relatively brief periods following applications of mineral N fertilisers (e.g. 75% of total annual
emissions were observed in the three 4-week periods following N applications to silage
grassland (Dobbie et al., 1999; Dobbie and Smith, 2003a). Sometimes the observed EF for
the relatively short periods between successive fertilisations can be well in excess of the
IPCC “default emission factor” of 1.25 ± 1.0%, even though this factor strictly applies to
emissions measured over a full 12 month period, or at least over a whole growth season.
The most dramatic example observed in the series of NT26 studies was at the Hillsborough
site in 2003, where the EF for the 2nd N application was 11.0% for CAN, 4.47% for urea, and
4.63% for urea+Agrotain. In the same year, and again after the 2nd N application, the EF for
CAN at Crichton was 4.56%, and for AN 1.92%. In these more extreme circumstances –
when N is actually applied to very wet and warm soils (or when heavy rain increases the
WFPS to >80% very soon after N addition) – the highest EFs are usually associated with
nitrate-containing fertiliser forms (AN or CAN). However, in only one of the NT2605 series of
experiments reported here was there a significant decrease in emissions from using AN
instead of urea. The EFs for urea modified by the addition of Agrotain are on average just
under half those for unmodified urea. Even with the addition of a further 6 sites in 2004/2005
to the 6 sites investigated in 2003, there are still too few data to give a very robust
assessment of the emissions associated with new fertiliser materials such as the various
urea and Agrotain combinations, as compared with those from unmodified urea.
5.2 Background emissions
It is clear from the experiments conducted under both NT2603 and NT2605 that the
background emissions (i.e. those from plots not receiving any N fertiliser, but otherwise
managed similarly to the N-fertilised ones) can vary substantially between sites. Thus in
2003, the range for the whole season was between 0.14 kg N 2O-N ha-1 (Rowden, grassland)
and 1.52 kg N2O-N ha-1 (Hillsborough, grassland). For 2004, the lowest flux was at Crichton
(grassland), at 0.85 kg N2O-N ha-1, and the highest was from Rowden (grassland), at 1.97 kg
N2O-N ha-1, while the Terrington site (the only arable one) was intermediate (1.52 kg N 2O-N
ha-1). The major difference between the IGER results for successive years appears to be
due to the fact that the experiment was located on a humose soil at Rowden Copse (14%
OM) in 2004, but on a mineral soil (De Bathe) with low OM in 2005. In the former site, more
N mineralisation would be expected to occur, thus increasing the necessary mineral N
substrate for nitrification/denitrification pathways to N2O. In 2005, the De Bathe (grassland)
site showed a negative flux (net uptake from the atmosphere), while both the arable sites
(Bush and Boxworth) gave moderate background emissions of 0.38 and 0.49 kg N2O-N ha-1,
respectively. Clearly, it is important to make background measurements at any site, so that
net emissions from the added N fertiliser can be calculated; if this is not done, on some
occasions the errors created by attributing all the emissions to the applied N will be small,
but on others they will be quite substantial.
25
________________________________________________________________________________
5.3 Impact of indirect emissions
So far, in this report, N2O-N EFs have been expressed as a percentage of fertiliser-N
applied, without any account being taken of prior losses of fertiliser N via ammonia
volatilisation. However, since these prior losses were 10 times greater from urea than from
AN (WP1b, Chadwick et al., 2005) a better comparison of direct N2O emissions would be
obtained from expressing the N2O-N EF as a percentage of fertiliser-N that actually enters
the soil, i.e. N applied – ammonia N emitted.
Taking all the full-season EFs for AN and urea from both the NT2603 and NT2605 results
together (12 experiments; and including CAN for the Hillsborough site in 2003 with the AN
values, as AN could not be used there), the overall mean EFs are 2.02% for AN and 1.51%
for urea. Correcting for the actual amount of AN entering the soil, the effective EF becomes
(1/0.975)  2.02 = 2.07%, while the corresponding value for urea is (1/0.75)  1.51 = 2.01%.
If one then applies the IPCC default value of 1% of the volatilised/redeposited N being
converted to N2O and combines this value with that for the direct emission, this will increase
the overall “effective EF” for AN to 2.1%; there is a larger increase for urea because of the
greater proportion volatilised, giving an effective EF of 2.26%. The difference between these
“effective EFs” for the two N forms is not significant.
26
________________________________________________________________________________
6. Key Conclusions
1. Taking the results from NT2603 and the NT2605 programmes together, the conclusion
reached after the former programme, that the data broadly bear out the relationships
obtained in earlier studies for Defra, remains the same. The results show a strong
dependence of N2O emission on soil wetness, temperature and the presence of sufficient
mineral N in the soil, which decreases rapidly after N application mainly as a result of
plant uptake.
2. These controlling variables can result in very large variations in EFs observed for
individual fertiliser applications, with some values much above and some well below the
IPCC default values. However, when several fertiliser applications are made during a
season, the overall mean EF for the whole N input over the whole season varies less
dramatically.
3. Predicting the actual level of these much enhanced emissions when they occur requires
a suitable model; the data obtained in both NT2603 and NT2605 should provide suitable
material to test such models of N2O emissions, as and when they become available.
4. Taking all the full-season EFs for AN and urea from both the NT2603 and NT2605 results
together (12 experiments), the overall mean EFs are 2.02% for AN and 1.51% for urea.
However, the difference in mean EF for direct emissions from AN and urea is more than
cancelled out by taking account of associated indirect emissions, and the overall EF for
both direct and indirect pathways is not significantly different.
5. Seasonal background emissions at the various sites have ranged between small negative
values (i.e. net uptake from the atmosphere) to nearly 2 kg N 2O-N ha-1. Thus it is
important to make background measurements at any site, so that net emissions from the
added N fertiliser can be calculated; if this is not done, on some occasions the errors may
be quite substantial.
6. Taking all the data from the 6 sites studied in 2003 and the 6 more studied in 2004/2005,
there is some indication that the EFs for new fertiliser materials such as the various
urea/Agrotain combinations are somewhat lower than those from unmodified urea.
However, the data are still too few to give a very robust assessment.
27
________________________________________________________________________________
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30
Appendix 1
Site details
Site
SAC
Crichton
2004
Grass
Netherwood
Loaning Field
Sandy loam
over sandstone
drift
ADAS
Terrington
2004
Arable
Tebbs Middle
IGER
De Bathe
2005
Grass
Halse 1
SAC
Bush
2005
Arable
House Field
ADAS
Boxworth
2005
Arable
Thorofare
Blacktoft
Deep sandy
loam (Crediton)
Deep sandy
clay loam
(Alluvial fans)
pH
%Org C
PSD
6.3
4.34
8.1
1.67
6.7
1.45
6.1
2.44
Calc clay over
chalky boulder
clay
(Hanslope)
8.2
2.4
<2µ (clay C)
2-20µ (fine silt FZ)
20-63µ (coarse silt CZ)
63-212µ (fine sand FS)
212-600µ (medium sand MS)
600µ - 2mm (coarse sand CS)
Bulk density 0-7.5cm
14
19
16
28
14
6
1.3
32
24
36
7
1
0
1.4
16
17
13
27
16
11
1.6
15
12
12
33
21
7
1.15
50
19
9
12
7
2
1.20
Study year
Grass/arable
Field name
Soil type (soil series)
IGER
Rowden
2004
Grass
Rowden Copse
Sandy silt loam
over clay
Soil analyses carried out on 0-7.5 cm depth for grass sites and 0-15 cm depth for arable sites unless specified otherwise
Appendix 2
Fertiliser applications – dates and amounts
Dates of N application and amounts applied
N1
Site/ Year/ Crop
N2
-1
N3
-1
N4
Date
kg N ha
Date
kg N ha
Date
kg N ha
Rowden 2004 (Grass)
02.03.04
40
31.03.04
80
24.05.04
100
Crichton 2004 (Grass)
10.03.04
40
31.03.04
80
10.05.04
100
Terrington 2004, (W. wheat)
02.03.04
40
05.04.04
90
07.05.04
90
De Bathe 2005 (Grass)
28.02.05
40
04.04.05
80
Bush 2005 (W. wheat)
10.03.05
40
20.04.05
90
06.05.05
90
Boxworth 2005 (W. wheat)
09.03.05
40
19.04.05
60
11.05.05
60
-1
Date
kg N ha-1
19.07.04
80
________________________________________________________________________________
Appendix 3
N2O emissions, soil WFPS, temperature and mineral N data for each site
Site 1. Rowden, 2004 (grassland)
350
300
AN
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
300
350
250
200
150
100
50
250
200
150
100
50
0
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
350
350
300
U+Ag1000(c)
N2O-N (g ha-1 d-1)
-1
N2O-N (g ha-1 d )
300
250
200
150
100
50
250
200
150
100
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
350
350
300
UAS
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
U+Ag500(c)
50
0
300
U
250
200
150
100
50
C
250
200
150
100
50
0
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Figure 2A.1. N2O emissions from each N fertiliser type
33
________________________________________________________________________________
Site 1. Rowden, 2004 (grassland)
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
N2O-N (g ha d )
1000
10000
-1
-1
10
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
12000
N2O-N (g ha )
-1
100
14000
8000
6000
4000
1
2000
0.1
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1st fert
2nd fert
3rd fert
4th fert
total
Date
Figure 2A.2. N2O emissions from each N fertiliser
type - composite graph, log scale
Figure 2A.3. Total N2O emissions after each fertiliser
application and seasonal totals
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
25
100
WFPS (%)
o
Soil temperature ( C)
120
20
15
10
80
60
40
5
20
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
Date
Figure 2A.4. Soil temperature
Figure 2A.5. Soil WFPS and timing of N applications
100
50
0
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
300
-1
150
NO3-N (mg kg dry soil)
400
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
-1
NH4-N (mg kg dry soil)
200
200
100
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
Date
Figure 2A.6. Soil ammonium-N
Figure 2A.7. Soil nitrate-N
34
________________________________________________________________________________
Site 2. Crichton, 2004 (grassland)
150
150
U
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
AN
100
50
0
100
50
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
150
150
U+Ag500(c)
N2O-N (g ha-1 d-1)
-1
N2O-N (g ha-1 d )
U+Ag1000(c)
100
50
0
100
50
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
150
150
C
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
UAS
100
50
0
100
50
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
35
________________________________________________________________________________
Site 2. Crichton, 2004 (grassland)
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
4000
3000
-1
N2O-N (g ha )
-1
-1
N2O-N (g ha d )
100
10
1
2000
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
1000
0.1
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1st fert
2nd fert
3rd fert
total
Date
100
80
15
WFPS (%)
o
20
10
60
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
40
5
20
0
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
Date
200
100
0
-1
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
300
-1
100
AN
U
U+Ag1000(c)
U+Ag500(c)
UAS
C
80
60
40
20
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
Figure 2A.14 Soil nitrate-N
36
________________________________________________________________________________
Site 6. Terrington, 2004 (w. wheat)
350
300
AN
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
300
350
250
200
150
100
200
150
100
50
50
0
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
350
350
300
U
-1
N2O-N (g ha-1 d )
N2O-N (g ha-1 d-1)
300
250
200
150
100
200
150
100
50
0
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
350
350
300
UAN
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
U+Ag1000(c)
250
50
300
C
250
250
200
150
100
250
200
150
100
50
50
0
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
UAN+Ag1000
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
37
________________________________________________________________________________
Site 6. Terrington, 2004 (w. wheat)
AN
U
U+Ag1000(c)
UAN
UAN+Ag1000
C
3000
-1
-1
N2O-N (g ha )
-1
N2O-N (g ha d )
100
4000
10
1
2000
AN
U
U+Ag1000(c)
UAN
UAN+Ag1000
C
1000
0.1
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1st fert
2nd fert
3rd fert
total
Date
100
15
10
5
80
60
40
0
20
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
Date
40
120
AN
U
U+Ag1000(c)
UAN
UAN+Ag1000
C
AN
U
U+Ag1000(c)
UAN
UAN+Ag1000
C
100
80
-1
-1
80
60
AN
U
U+Ag1000(c)
UAN
UAN+Ag1000
C
120
WFPS (%)
o
20
20
0
60
40
20
0
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
1.3.04 1.5.04 1.7.04 1.9.04 1.11.04 1.1.05
Date
38
________________________________________________________________________________
Site 8. Halse, 2005 (grassland)
120
120
AN
80
60
40
20
0
1.5.05
1.7.05
60
40
20
1.9.05
1.3.05
120
1.5.05
1.7.05
1.9.05
120
U+Ag500(m)
-1
80
60
40
20
U+Ag250(m)
100
N2O-N (g ha-1 d-1)
100
N2O-N (g ha-1 d )
80
0
1.3.05
0
80
60
40
20
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
120
1.5.05
1.7.05
1.9.05
120
U+Ag500(c)
80
60
40
20
0
C
100
N2O-N (g ha-1 d-1)
100
N2O-N (g ha-1 d-1)
U
100
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
100
80
60
40
20
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
1.7.05
1.9.05
39
________________________________________________________________________________
Site 8. Halse, 2005 (grassland)
AN
U
U+Ag500(m)
U+Ag250(m)
U+Ag500(c)
C
1000
1000
-1
10
-1
AN
U
U+Ag500(m)
U+Ag250(m)
U+Ag500(c)
C
1200
N2O-N (g ha )
-1
N2O-N (g ha d )
100
1400
1
0.1
800
600
400
200
0.01
0
0.001
-200
1.3.05
1.5.05
1.7.05
1.9.05
1st
2nd
total
Date
AN
U
U+Ag500(m)
U+Ag250(m)
U+Ag(c)
C
120
100
20
WFPS (%)
o
25
15
10
5
80
60
40
20
0
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
Date
1.9.05
Date
100
-1
60
40
20
0
-1
AN
U
U+Ag500(m)
U+Ag250(m)
U+Ag500(c)
C
80
1.7.05
AN
U
U+Ag500(m)
U+Ag250(m)
U+Ag500(c)
C
80
60
40
20
0
1.3.05
1.5.05
1.7.05
1.9.05
Date
1.3.05
1.5.05
1.7.05
1.9.05
Date
40
________________________________________________________________________________
Site 13. Bush, 2005 (w. wheat)
250
AN
200
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
250
150
100
50
0
1.5.05
1.7.05
100
50
1.9.05
1.3.05
250
1.5.05
1.7.05
1.9.05
250
U
200
U+Ag500(m)
200
-1
N2O-N (g ha-1 d )
N2O-N (g ha-1 d-1)
150
0
1.3.05
150
100
50
0
150
100
50
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
250
1.5.05
1.7.05
1.9.05
250
UAN
200
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
C
200
150
100
50
0
UAN+Ag500
200
150
100
50
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
1.7.05
1.9.05
41
________________________________________________________________________________
Site 13. Bush, 2005 (w. wheat)
-1
10
1
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
5000
-1
-1
N2O-N (g ha d )
100
6000
N2O-N (g ha )
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
4000
3000
2000
1000
0.1
0
1.3.05
1.5.05
1.7.05
1.9.05
1st fert
2nd fert
3rd fert
total
Date
20
100
15
80
WFPS (%)
o
10
5
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
60
40
0
20
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
Date
60
120
100
80
60
40
20
0
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
50
40
-1
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
140
160
-1
1.9.05
Date
1.7.05
30
20
10
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
1.7.05
1.9.05
Date
Date
42
________________________________________________________________________________
Site 14. Boxworth, 2005 (w. wheat)
50
50
AN
30
20
10
0
1.5.05
1.7.05
20
10
1.9.05
1.3.05
50
1.5.05
1.7.05
1.9.05
50
U
U+Ag500(m)
40
-1
N2O-N (g ha-1 d )
40
N2O-N (g ha-1 d-1)
30
0
1.3.05
30
20
10
0
30
20
10
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
50
1.5.05
1.7.05
1.9.05
50
UAN
30
20
10
0
UAN+Ag500
40
N2O-N (g ha-1 d-1)
40
N2O-N (g ha-1 d-1)
C
40
N2O-N (g ha-1 d-1)
N2O-N (g ha-1 d-1)
40
30
20
10
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
1.7.05
1.9.05
43
________________________________________________________________________________
Site 14. Boxworth, 2005 (w. wheat)
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
1500
-1
-1
N2O-N (g ha )
-1
N2O-N (g ha d )
100
2000
10
1
0.1
1000
500
0
1.3.05
1.5.05
1.7.05
1.9.05
1st fert
2nd fert
3rd fert
total
Date
20
100
15
80
WFPS (%)
o
10
5
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
60
40
0
20
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
Date
100
60
40
20
0
-1
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
80
100
-1
1.9.05
Date
1.7.05
AN
U
U+Ag500(m)
UAN
UAN+Ag500
C
80
60
40
20
0
1.3.05
1.5.05
1.7.05
1.9.05
1.3.05
1.5.05
1.7.05
1.9.05
Date
Date
44

WP2 The effect of N fertiliser forms on nitrous oxide

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