Stabilised nitrogen fertilisers to reduce
greenhouse gas emissions and improve
nitrogen use efficiency in Australian agriculture
Helen Suter, Deli Chen, Debra Turner
Melbourne School of Land and Environment
The University of Melbourne
Background
• Nitrogen Use Efficiency
– 6-60% plant N uptake
– Losses
• NH3
• Leaching (NO3-)
• Other gases (N2O, NOx)
Urea consumption Australia
= 1.1 million tonnes/ yr
Variable and potentially large losses;
up to 57%
economics, environment,
health
Indirect GHG
N2O EF; 1.0%
environment
Background
• Nitrogen Use Efficiency
– 6-60% plant N uptake
– Losses
• NH3
• Leaching (NO3-)
• Other gases (N2O, NOx)
•EF; 0.05 – 2.8%
Australian total (25 Mt CO2-e)
•76% = agriculture
•~38% = mineral fertiliser use
environment
economic – C trading
Lost nutrient
Indirect GHG;
N2O EF; 1.0%
environment
economic
Background
• Stabilised fertilisers – Urease inhibitor (Part 1)
• NH3 loss
– Nitrification inhibitor (Part 2)
• N2O
• NO3-
• Variable outcomes – emissions
– productivity gains
Greatest benefit?
x
x
x
x x
Image source: http://www-cluster.bom.gov.au/climate/environ/other/kpn_group.shtml
Part 1 : Urease Inhibitors
Reducing ammonia (NH3) loss
NH4+/ NH3
NH3
urease Urea CO(NH2)2
+ H2O + CO2 + H2O/OH-
•High loss possible
X
0
20
40
60
80
100
0 2 4 6 8 10 12
Ure
a r
em
ain
ing (
%)
Days after fertiliser application
Urea 15
Urea 25
Urea 35
Urea+NBPT 15
Urea+NBPT 25
Urea+NBPT 35
a) clay loam
0
20
40
60
80
100
0 2 4 6 8 10 12
Ure
a r
em
ain
ing (
%)
Days after fertiliser application
b) clayey sand
Urea hydrolysis
Clay loam Clayey sand
pH 5.5 7.3
Clay 20 9
Organic C (%) 3.9 0.5
Urease activity (mg urea-N/g soil/hr) 134 43
0
1
2
3
4
5
6
0 2 4 6 8 10
NH
3lo
ss r
ate
(kg N
ha
-1d
-1)
Days after fertiliser application
0
2
4
6
8
10
12
0 4 8 12 16 20 24
NH
3lo
ss (
kg
N h
a-1
)
Days after fertiliser application
NH3 loss
N0=80 kg N/ha
N0=40 kg N/ha
Urea
Urea + NBPT
Cropping; cumulative flux
Pasture; daily flux Pasture; cumulative flux
cropping pasture
pH 7.3 5.5
Organic C (%) 1.3 2.4
Clay (%) 33 22
0
2
4
6
8
10
12
0 4 8 12 16 20 24
NH
3lo
ss (
kg
N h
a-1
)
Days after fertiliser application
NH3 loss N0=80 kg N/ha
N0=40 kg N/ha
Urea
Urea + NBPT
Cropping
Pasture
9.5%
1% 89% reduction
30%
9% 70% reduction
{Pasture, spring: 2% loss with urea}
N use efficiency
• 15N – 73% recovery – Plant: 42%
– Soil: 31% (H. Sultana, UoM)
• Dry matter production (kg/ha) increase per
unit N (kg) addition (autumn); – 8 (urea)
– 7 (urea + NBPT)
Part 2. Nitrification Inhibitors
Reducing N2O emissions and NO3- leaching
NH4+/ NH3
NO2-
Am
monia
oxid
izers
NO3-
N2O •GHG
Nitrification
Denitrification
Nutrient loss
X
Nitrification Inhibitors : Nitrate production
– temperature
0
100
200
300
400
500
600
700
0 10 20 30 40 50 60 70 80
Nit
rate
+ N
itri
te (m
g N
/g s
oil
)
days after fertiliser application
a) 15oCControl (no fertiliser)
Ammonium sulphate
Ammonium sulphate + DMPP
0
100
200
300
400
500
600
700
0 10 20 30 40 50 60 70 80
Nit
rate
+ N
itri
te (m
g N
/g s
oil)
days after fertiliser application
b) 35oC
Nitrification Inhibitors : N2O
0.0
0.5
1.0
1.5
2.0
0 10 20 30 40 50 60 70
N2O
(g/h
a)
days after fertiliser application
a) 15oC, daily flux C
AS
DMPP
0.0
0.5
1.0
1.5
2.0
0 10 20 30 40 50 60 70
N2O
(g/h
a)
days after fertiliser application
b) 35oC, daily flux
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70
N2O
(g/
ha)
days after fertiliser application
c) 15oC, cumulative flux
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70
N2O
(g/h
a)
days after fertiliser application
d) 35oC, cumulative flux
Soils used in laboratory experiments
Location Use Clay (%) pHw Org. C (%)
NSW grains 39 8.0 1.5
Qld sugarcane 13 4.8 1.5
Qld sugarcane 13 5.5 0.7
Qld sugarcane 39 5.3 3.1
Vic dairy pasture 21 5.4 10
Vic dairy pasture 33 5.5 2.4
Vic conversion 24 5.5 6.2
Vic conversion 21 5.5 7.3
Vic cropping 30 7.8 1.3
Summary of selected soil properties
Nitrification Inhibitors
N2O emissions and temperature
• Inhibitory effect
– N2O reduction: 0-95%
• Soil
– ? pH
– ? Clay content
– ? Organic C
– ? Nitrification rate
• Temperature: reduced inhibition
– Soil
– Inhibitor
Nitrification Inhibitors
DMPP; 64% reduction in net-N2O over 8 months
Biomass response to DMPP; • After extended period (2 months) with no
fertiliser application
• Over winter
•Leaching component?
Greatest N2O emission in spring - warming soil temperatures
[increase from 11 to 20oC @ 10 cm depth]
Conclusions : potential for inhibitors
in Australian agriculture
Inhibitor NH3 N2O
Nitrogen use
efficiency
Drivers of
performance
Urease inhibitor x / ? ?
•Soil
(pH, urease activity,
organic C)
•Climate (*rainfall)
•Temperature
Nitrification
inhibitor ? / ?
•Temperature
• Soil
(pH, clay %, organic
C)
Conclusions : benefits from inhibitors
in Australian agriculture
• Considerations – environment
• soils, climate
– N savings potential
• industry, nutrient management
Inhibitor Greatest benefit
Urease inhibitor
•Surface applied urea
•High emission environments
organic
low moisture
windy
Nitrification inhibitor
•High losses as
- N2O
- leaching
Thank you
• http://www.piccc.org.au/
• http://www.n2o.net.au/
