Ammonia emissions from urea, stabilized urea and calcium ammonium nitrate: insights into loss abatement in temperate grassland

TLDR: The grant numbers were RSF 13S430, RSF 11S138 and RSF 14S430 as mentioned in this paper for the Irish Department of Agriculture Food and Marine (DFAF).

Abstract: Irish Department of Agriculture Food and Marine. Grant Numbers: RSF 13S430, 11S138.Teagasc Walsh Fellowship Programme

Figures

Figure 2 Hourly ammonia (NH3) emissions by fertiliser N treatment, daily precipitation and mean daily air temperature for each fertiliser N application date at the Hillsborough site.

Table 2 Annual ammonia loss as measured by wind tunnels and the change (Δ) in loss compared with the urea 200 kg N/ha rate for the other treatments. N applied to grassland N input in five equal split applications (40 or 80 kg N/ha).

Table 1 Ammonia loss as affected by fertiliser N treatment for each application date at the Johnstown Castle and Hillsborough sites. Site Johnstown Castle Hillsborough Season Spring Summer Spring Summer b Fertiliser application date Mar 10 Apr 28 Jun 3 Jul 7 Aug 18 Mar 24 May 6 Jun 9 Jul 28 Sept 8 Volumetric moisture 0-5cm on day after application (%) 45.4 37.4 34.4 28.8 27.5 46 41.7 24.9 16.8 25.5 Treatment N rate/

Figure 1 Hourly ammonia (NH3) emissions by fertiliser N treatment, daily precipitation and mean daily air temperature for each fertiliser N application date at the Johnstown Castle site.

Full text

TITLE: Ammonia emissions from urea, stabilised urea and calcium ammonium
nitrate: insights into loss abatement in temperate grassland
AUTHORS: Patrick J. Forrestal, Mary Harty, Rachael Carolan, Gary J. Lanigan,
Catherine J. Watson, Ronnie J. Laughlin, Gavin McNeill, Brian J. Chambers, Karl G.
Richards
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NOTICE: This is the peer reviewed version of the following article: Soil Use and Management,
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Title: Ammonia emissions from urea, stabilised urea and calcium ammonium nitrate:
insights into loss abatement in temperate grassland
Authors and order: Patrick J. Forrestal
1
, Mary Harty
1,2
, Rachael Carolan
3
, Gary J. Lanigan
1
,
Catherine J. Watson
2,3
,
Ronnie J. Laughlin
3
, Gavin McNeill
3
, Brian J. Chambers
4
, Karl G.
Richards
1
1
Crops Environment and Land Use Program, Teagasc, Johnstown Castle, Wexford, Ireland.
2
Queen’s University Belfast, University Road, Belfast BT7 1NN, Northern Ireland.
3
Agri-Food and Biosciences Institute (AFBI), Newforge Lane, Belfast BT9 5PX, Northern
Ireland.
4
ADAS Gleadthorpe, Meden Vale, Mansfield, Nottinghamshire NG20 9PD, U.K.
Corresponding author: Patrick J. Forrestal
1
patrick.forrestal@teagasc.ie
Short running head title: Ammonia emissions from fertilisers

Abstract
Fertiliser nitrogen (N) contributes to ammonia (NH
3
) emissions, which European Union
member states have committed to reduce. This study evaluated NH
3
-N loss from a suite of N
fertilisers over multiple applications, and on gaining insights into the temporal and seasonal
patterns of NH
3
-N loss from urea in Irish temperate grassland using wind tunnels. The
fertilisers evaluated were: calcium ammonium nitrate (CAN), urea, and urea with the N
stabilisers N-(n-butyl) thiophosphoric triamide (NBPT), dicyandiamide (DCD), DCD+NBPT,
and a maleic and itaconic acid polymer (MIP). 200 (and 400 for urea only) kg N/ha/yr was
applied in five equal applications over the growing season at two grassland sites (one for
MIP). Mean NH
3
-N losses from CAN were 85% lower than urea which had highly variable
loss (range 45% points). The effect of DCD on NH
3
emissions was variable. MIP did not
decrease loss but NBPT caused a 78.5% reduction, and when combined with DCD, a 74%
reduction compared with urea alone. Mean spring and summer losses from urea were similar,
although spring losses were more variable with both the lowest and highest loss levels.
Maximum NH
3
-N loss usually occurred on the second day after application. These data
highlight the potential of stabilised urea to alter urea NH
3
-N loss outcomes in temperate
grassland, the need for caution when using season as a loss risk guide and that urea
hydrolysis and NH
3
-N loss in temperate grassland is rapid. Micrometeorological
measurements focused specifically on urea are needed to determine absolute NH
3
-N loss
levels in Irish temperate grassland.
Key words: ammonia, volatilisation, urea, ammonium nitrate, inhibitors, grassland, fertiliser

Introduction
Global ammonia (NH
3
) emissions from fertiliser nitrogen (N) are estimated at 10 to
12 Tg N/yr
(Beusen et al., 2008). These emissions are of concern from economic,
environmental, and national policy perspectives. As addition of supplemental fertiliser N is a
cornerstone of many agricultural systems N lost as NH
3
-N must be replaced, typically at an
economic and environmental cost, in order to sustain agro-ecosystem productivity. Ammonia
lost from agricultural systems may be re-deposited contributing to eutrophication and
acidification of terrestrial and aquatic ecosystems (Sutton et al. 1992) and indirect emissions
of nitrous oxide (N
2
O), a potent greenhouse gas. In terms of national policy, EU member
states have committed to reducing NH
3
-N emissions under the National Emissions Ceiling
Directive (EU, 2001).
The use of urea in place of ammonium nitrate-based fertiliser has some potential for
mitigating fertiliser N related N
2
O emissions (Dobbie & Smith, 2003). However, urea is
vulnerable to NH
3
volatilisation (Chambers & Dampney 2009). Promisingly N stabilised
using N inhibitors can play a role in mitigating losses of NH
3
-N (Watson et al., 2009), N
2
O
(Di et al., 2007) and nitrate
leaching (Dennis et al. 2012). These inhibitors can be divided into
two groups: i) urease inhibitors and ii) nitrification inhibitors. Urease inhibitors reduce NH
3
volatilisation from urea by inhibiting the enzyme urease which catalyses urea hydrolysis. The
urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) has been shown to reduce NH
3
loss from urea (Watson et al., 1990, 1994; Goos et al., 2013). The maleic and itaconic acid
polymer (MIP) has been marketed globally and claims to be a urease and a nitrification
inhibitor. However, a number of studies (Franzen et al., 2011; Goos et al., 2013) have shown
that urea treated with MIP did not reduce NH
3
loss from urea. Nitrification inhibitors, such as
dicyandiamide (DCD), inhibit ammonia monooxygenase, which catalyses oxidation of
ammonium (NH
4
+
) to nitrite (Kim et al. 2012). Although effective for reducing N
2
O

emissions and leaching, nitrification inhibitors may increase NH
3
emissions. In a meta-
analysis, Kim et al. (2012) reported that the effect of DCD on NH
3
emissions was
inconsistent, with increased NH
3
emissions in 26 studies, no change in 14 studies and
decreased emissions in 6 studies. They linked nitrification inhibitor related increases in NH
3
loss to increasing soil pH and decreasing cation exchange capacity (CEC).
Previous studies have evaluated NH
3
loss from urea and urea with inhibitors,
particularly in cropping systems; however field measurements in temperate grassland are
more limited. To address this knowledge deficit, the current study assessed NH
3
-N loss from
fertiliser formulations with and without N stabilisers over multiple applications.
Materials and methods
Site description and experimental design
Experiments were conducted at grassland sites located at Hillsborough (HB), Co.
Down, Northern Ireland (54°46′N; 6°08′W) and Johnstown Castle (JC), Co. Wexford, Ireland
(52°17′N; 6°30′W). Hillsborough is a moderately drained loam classified as a Dystric Umbric
Stagnosol (FAO, 2014) (45% sand, 33% silt, 22% clay, 11% organic matter, pH 5.6, CEC
24.43 cmol
+
/kg). Johnstown Castle is a moderately drained loam classified as a Stagnic
Cambisol (FAO, 2014) (52% sand, 34% silt, 14% clay, 7% organic matter, pH 5.8, CEC
15.46 cmol
+
/kg). Swards were dominated by perennial ryegrass (Lolium perenne L.).
Precipitation, ambient and soil temperature were measured by a meteorological station (ca.
500 m from the study site). A HH2 moisture meter (Delta Devices, Burwell, Cambridge,
England) was used to measure soil volumetric moisture content on site.
Fertiliser treatments were applied in five equal split applications. Treatments were CAN,
urea, urea+NBPT, urea+DCD, urea+NBPT+DCD and at JC only urea+MIP. All treatments
were applied at 200 kg N/ha and both sites also included a urea 400 kg N/ha/yr treatment.

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Title: ammonia emissions from urea, stabilised urea and calcium ammonium nitrate: insights into loss abatement in temperate grassland authors:" ?

This study evaluated NH3-N loss from a suite of N fertilisers over multiple applications, and on gaining insights into the temporal and seasonal patterns of NH3-N loss from urea in Irish temperate grassland using wind tunnels. These data highlight the potential of stabilised urea to alter urea NH3-N loss outcomes in temperate grassland, the need for caution when using season as a loss risk guide and that urea hydrolysis and NH3-N loss in temperate grassland is rapid. 

Q2. What is the effect of nitrification inhibitors on NH3 emissions?

Nitrification inhibitors, such as dicyandiamide (DCD), inhibit ammonia monooxygenase, which catalyses oxidation of ammonium (NH4 + ) to nitrite (Kim et al. 2012). 

Q3. What is the effect of applying a urea loss factor to the nationally utilised?

Applying a NH3-N loss factor to the nationally utilised volume of urea, to the exclusion of the rate effect will introduce added uncertainty to loss estimates. 

Q4. What is the effect of supplemental fertiliser N on NH3 emissions?

As addition of supplemental fertiliser N is a cornerstone of many agricultural systems N lost as NH3-N must be replaced, typically at an economic and environmental cost, in order to sustain agro-ecosystem productivity. 

Q5. What is the effect of nitrification inhibitors on soil NH3-N?

Aisling et al. (2008) reported that NH4 + remains in the soil longer when a nitrification inhibitor is used, with approximately 40% more NH4 + -N in the soil one day after application when DCD was used with urea. 

Q6. Why were wind tunnels chosen for the current study?

Wind tunnels were chosen for the current study because they permitted inter-comparison of a large suite of fertilisers in replicate, which would not have been practical using IHF which requires homogeneous fetch and relatively large land areas. 

Q7. What is the effect of precipitation on NH3-N loss in temperate grasslands?

large NH3-N losses from urea can occur over time in temperate grasslands when precipitation does not arrest loss even under cooler conditions as was seen following the March 10 application at JC. 

Q8. How many times did Ryden & Lockyer find that wind tunnels can overestimate?

Ryden & Lockyer (1985) found that wind tunnels can overestimate NH3-N losses by a factor of 2.4 to 6 during periods of rainfall. 

Q9. What is the effect of urea on NH3 emissions?

The use of urea in place of ammonium nitrate-based fertiliser has some potential formitigating fertiliser N related N2O emissions (Dobbie & Smith, 2003). 

Q10. What is the effect of nitrification inhibitors on NH3-N loss?

The current data show that this is also an issue in temperate grassland, with DCD significantly increasing NH3-N loss at JC at three applications (by 15.8% to 23.9 percentage points, Table 1) and having no effect at two applications. 

Q11. What is the effect of NBPT on NH3-N loss?

This is similar to the 78.5% reduction when the urease inhibitor was used alone, thus NBPT inclusion with DCD may be a strategy for overcoming the variable NH3-N loss responses associated with DCD. 

Q12. What was the effect of urea on NH3-N loss?

the present study demonstrated that the NH3-N abatement potential of NBPT was on average 78.5% when used with urea alone or 74% when used in combination with the nitrification inhibitor DCD and that MIP had no significant effect on NH3-N loss. 

Q13. What is the relative humidity of urea in Irish grassland?

Urea is a hygroscopic substance with a critical relative humidity of 80% at 20 o C (Adams and Merz, 1929), a humidity level frequently surpassed in Irish grassland. 

Q14. What is the effect of precipitation on NH3-N loss in a temperate?

Black et al. (1985) noted no marked seasonal pattern of NH3-N loss from urea in New Zealand grassland with 13.1, 15 and 11.2% from a summer, autumn and winter application, respectively, although there was a slight tendency for lower loss in spring at 10%.