management impacts on nitrous oxide emissions from

Management Impacts on Nitrous Oxide Emissions from

Cropping Systems in Minnesota

Rodney Venterea

US Dept. of Agriculture - ARS

Dept. of Soil, Water, Climate / University of Minnesota

Michael Dolan

Jason Leonard

Anna Dwinnel

Ryo Fujinuma

Kurt Spokas

John Baker

Carl Rosen

Charles Hyatt

Bijesh Maharjan

Matt McNearney

Many undergraduate student technicians

FUNDING SOURCES •NRI-USDA CSREES/NIFA Air Quality Program

•USDA-ARS GRACEnet Project

•International Plant Nutrition Institute’s Foundation for Agronomic Research:

•Agrotain Intl.

•Agrium Inc.

•Minnesota Corn Growers Association

•John Deere & Company

•Kingenta Corporation

The Deepwater Horizon oil spill (leak)

April 20 - July 15, 2010

IS THERE ANYTHING WE CAN DO TO STOP THE LEAK(s) ?

Fukushima Dai-ichi Nuclear Power Plant

March 11, 2011 - ??

IS THERE ANYTHING WE CAN DO TO STOP THE LEAK(s) ?

IPCC, 2007.

The Leaking Nitrogen Cycle

Atmospheric Nitrous Oxide (N2O) Concentrations

1850 - ????

N2O (ppb)

1998 2000 2002 2004 2006 2008 2010 2012

Atm

os

ph

eri

c N

2O

( p

pt

)

312

314

316

318

320

322

324

Atmospheric N2O

NOAA/ESRL halocarbons in situ program ftp://ftp.cmdl.noaa.gov/hats/n2o/insituGCs/CATS/global/insitu_global_N2O.txt

Rising Atmospheric N2O

~ 20% above pre-industrial levels

Slope = 0.77 ppb y-1

r2 = 0.995

Fertilizer application: 40%

Manure application & mgmt: 40%

Biomass burning : 7%

Industrial: 14%

Davidson, 2009; Mosier et al.,1998

Anthropogenic N2O Sources

1960 1970 1980 1990 2000 2010

T

g N

fert

iliz

er

co

ns

um

ed

(ap

pro

x. %

of

cu

rren

t co

nsu

mp

tio

n)

0

5

10

15

20

25

30

35China, 34% of total

India, 15%

U.S., 11%

Pakistan, 3%

Indonesia, 2.8%

African Continent, 2.8%

Brazil, 2.5%

France, 2.1%

Canada, 1.8%

Bangladesh, 1.2%

87% of total increase since 1980 occurred in China and India

http://www.fertilizer.org/

China

U.S. India

World Fertilizer Use

2 kg N2O-N = CO2 from

100 gallons of gasoline

Global Warming Potential (GWP) = 300 times CO2

2 kg N2O-N ha-1 ≈ 1 Mg CO2 ha-1

IPCC, 2007

% of total anthropogenic GHG emissions

Global Warming Potential (GWP) = 300 times CO2

ODP = Ozone Depleting Potential

N2O

Ravishankara et al. Science. 2009

“By 2050, N2O emissions could

represent > 30% of peak CFC

emissions of 1987.”

Tg

CO

2 E

qu

ivale

nts

0

100

200

300

Soil CO2

flux

On-farm energy use

CH4N2O

USEPA, 2008.

Greenhouse Gas Sources

in U.S. Agriculture (2006)

GWP= Global Warming Potential

Policy activity & demands

e.g., 2008 Farm Bill Requires USDA to develop scientifically-based

guidelines to allow individual farming operations to

quantify their N2O and overall GHG emissions.

Few studies examining N fertilizer management practices

• Comparison of fall- vs. spring- applied AA: 1 study (0 in MN)

• Comparison of AA with and w/out N serve: 1 study (0 in MN)

• Single versus split applications: 1 study (0 in MN)

• Few empirically-based guidelines for reducing N2O while maintaining crop yields

Fertilizer Management Effects

Review our recent research regarding synthetic N fertilizer mgmt effects:

1. Controlled release fertilizers (CRFs)

2. Effects of different chemical fertilizer forms

3. Placement (depth and banding) effects

4. Mechanisms & modeling

5. Tillage effects

6. Nitrogen use efficiency (NUE)

Outline

X

X

X

Irrigated Site

-Corn

-Potato

Dryland/naturally drained site

-Corn

Dryland/

Tile-drained site

-Corn

Study Sites

Methods: Gas Flux Chambers

Pro:

• Plot-scale studies & treatment comparisons

• Inexpensive

Con:

• Limited spatial and temporal coverage

• Physical disturbance

Methods: Automated Chambers

5/1/06 6/1/06 7/1/06 8/1/06 9/1/06 10/1/065/1/05 6/1/05 7/1/05 8/1/05 9/1/05 10/1/05 11/1/05

0

100

200

300

400

500

AA

U

4/1/07 5/1/07 6/1/07 7/1/07 8/1/07 9/1/07 10/1/07

F P PF FP

Daily N2O flux (µg N m-2 h-1)

F = Fertilizer application date

P = Planting date

Trapezoidal

Integration

Flux versus Time

Data

Cumulative Emissions

mg N m-2 ug N m-2 h-1

(1 kg N ha-1 = 100 mg N m-2)

Methods: Data Analysis

Direct emissions

N2O

Managed

field boundary

Direct and Indirect N2O Emissions

Indirect emissions

N2O

NO NH3

NO3-

Challenges:

1. Logistical - measuring all forms of N loss in a single experiment

Chambers for NO and NH3; Lysimeters, water sampling for NO3-

2. Estimating fraction of off-site N losses converted to N2O

< 0.5 % to 5 %

~ 25% of

total national

emissions

40 – 50% for

some systems

Asynchrony between N fertilizer application and crop N demand

Iowa State University Extension

Corn N Uptake

High potential for generating N losses:

Provide substrate for soil microbial population

Preplant

53%

Fall application

35%

~ 10%

Controlled Release Fertilizers (CRFs) for Reducing N2O Emissions

GOAL: Achieve more gradual N release over growing season:

1. Polymer–coated urea (PCU): Slow diffusion through porous coating

H2O diffuses in

Urea diffuses out

© 2011Agrium Advanced Technologies (U.S.) Inc.

Polymer-coated Urea (PCU) for Irrigated Potato Production

Source Timing Rate (kg N ha-1)

1. Conventional urea (47%N) 4 split applications 270

2. PCU-1 (44%N) Before planting 270


Potato N Uptake

North Dakota State University Extension

Urea/UAN

PCUs

Controlled Release Fertilizers for Irrigated Potato Production

Hyatt et al. 2010. SSSAJ.

Three-yr mean N2O emissions

Becker, MN

N2O

em

issio

ns

(m

g N

m-2

)

0

50

100

150

200

Tu

ber

yie

lds (

ton

ha

-1)

0

50

100

150

200

Conventional Urea

Polymer-coated Urea 1


N2O emissions Tuber yields

a

ab

b





• N2O either decreased or same

• No yield difference

Venterea et al. 2011. JEQ





Controlled Release Fertilizers for Irrigated Potato Production

Soil and leaching data for individual yearsLoamy sand, Becker, MN

Resid

ual

So

il N

(m

g N

kg

-1)

0

10

20

30

40

50

60

So

il-w

ate

r n

itra

te (

mg

N L

-1)

0

10

20

30

40

50

60

Conventional Urea



Residual Soil N (year 1)

a a

b

a

ab

b

Nitrate in Soil-Water(Spring following year 2)

• N2O decreased

• NO3- leaching potential increased

• Net effect on total emissions?

Polymer-coated urea for reducing N2O emissions

Other studies:

• PCU-1 in irrigated and dryland corn at Becker: No decrease in N2O

• PCU-1 in dryland corn at Rosemount: No decrease in N2O

1. Potential advantages if product release rate is well matched to crop demand.

2. No set of guidelines for knowing when/where specific products will be effective

for reducing N2O emissions.

3. Widespread adoption of PCU-1 (ESN) in potato production: due to work of Rosen

et al. showing potential reduction in leaching (indirect N2O).

4. Minimal adoption for corn production (< 3%). Yield benefits required to justify

increased cost are not consistent.

Controlled Release Fertilizers (CRFs) for Reducing N2O Emissions

GOAL: Achieve more gradual N release over growing season:

2. Nitrification (NI) inhibitors: Blended or co-applied with fertilizer

NH4+ NO3

-

enzyme inhibitor

Controlled Release Fertilizers for Dryland Corn Production


1. Conventional urea (47%N) Sidedress (V4-V6) 146

2. Urea + DCD + NBPT (47%N) Sidedress (V4-V6) 146

Urea

Urea + NI +UI

Treatments applied to both CT and NT treatments (in place for > 15 yr)

Controlled Release Fertilizers for Dryland Corn Production


1. Conventional urea (47%N) Sidedress (V4-V6) 146

2. Urea + DCD + NBPT (47%N) Sidedress (V4-V6) 146

Venterea et al. 2011. JEQ

Three-yr mean N2O emissions

Rosemount, MN

N2O

(kg

N h

a-1

)

0

20

40

60

80

100

120

Conventional Urea

Urea with Inhibitors

Conventional Tillage No Till

Waukegan silt loam

Treatments applied to both CT and NT treatments (in place for > 15 yr)

No significant effect on N2O emissions (or yield)

1. Several studies, some potential for reductions, but varying success.

2. Many different chemical formulations, but little systematic comparison.

3. Few guidelines for knowing when/where specific products will be effective for

reducing N2O emissions.

4. Yield benefits required to justify cost are not consistent, not widespread use.

5. One exception: ~ 10% of MN corn producers use N-serve (nitrapyrin), mostly with

fall-applied N. Some studies: decreased Nitrate leaching potential. Recent study

in IA showed no reduction in direct N2O with N-serve.

Nitrification inhibitors for reducing N2O emissions

Other studies:

• In irrigated and dryland corn at Becker: No decrease in N2O

• In dryland corn at Rosemount: No decrease in N2O

Survey of MN corn producers (MDA/ UMN/ NASS, 2010)

Anhydrous ammonia = 46%

Conventional Urea = 45%

> 90%

Fertilizer Source Effects: Conventional Sources

Tera

gra

ms o

f N

itro

gen

0

1

2

3

4

Anhydrous Ammonia

Urea Solutions (UAN)

NH4 & NO3

salts

Other

Economic Research Service (2011)

(data for 2008)35%

23%

29%

4%

10%

Nitrogen Fertilizer Use by Type in U.S.

AA + Urea = 58%

Only 1 site-year of data comparing N2O emissions with AA and Urea prior to 2005

(Thornton et al., 1996)

Continuous corn Corn after soybeans

Three-yr average growing season N2O emissions

Rosemount, MN

N2O

(m

g N

m-2

)

0

100

200

300Anhydrous ammonia

Urea

b

a

b

a

Venterea et al. 2010. SSSAJ.

Anhydrous Ammonia versus Urea: Dryland Corn

Source Timing Placement Rate (kg N ha-1)

1. Urea (47%N) Pre-plant Broadcast and incorporated 146

2. AA (82%N) Pre-plant Injected into subsurface band 146

Treatments applied to both Corn following Corn and Corn following Soybean

Irrigated corn

Two-yr average growing season N2O emissions

Becker, MN

N2O

(m

g N

m-2

)

0

25

50

75

100

Anhydrous ammonia

Urea

b

a

Fujinuma et al., 2011 (submitted.)

Anhydrous Ammonia versus Urea: Irrigated Corn


1. Urea (47%N) Pre-plant/Sidedress Broadcast and incorporated 90 / 90

2. AA (82%N) Pre-plant/Sidedress Injected and banded 90 / 90

Summary of studies in corn systems

Emissions Factor (EF) Assessment

Study EFAA: EFurea

Thornton et al. (1996) 1.94

Venterea et al. (2010) 2.60

Fujinuma et al. (2011) 1.53

Average 2.0

Anhydrous Ammonia versus Urea

Worldwide AA Use

U.S. 85%

Canada 13%

Mexico 1%

Rest of world 1% (IFA Statistics)

1 study in Canada wheat system: No difference in emissions.

* Lower N application rate (80 kg N ha-1)

Is this enough evidence to drive a policy recommendation or

do we need more studies ?

Anhydrous Ammonia versus Urea: Indirect N2O Emissions

Fujinuma et al., 2011 (submitted); Maharjan et al., 2011 (in preparation)

N2O emitted

Direct and Indirect N2O emissions

Becker, MN

N2O

or

NO

(m

g N

m-2

)

0

25

50

75

100

NO

3

- (k

g N

ha

-1)

0

25

50

75

100Anhydrous ammonia

Ureab

a

NO emitted NO3

- leached

a

a

b b

Direct emissions

decreased with urea

Indirect emissions

increased with Urea


2006 IPCC Guidelines for National Greenhouse Gas Inventories. De Klein et al.


Lower limit of 95% CI0.2% of NO

0.05% of NO3

-

Total Direct plus Indirect N2O emissions

Becker, MN

To

tal N

2O

(m

g N

m-2

)

0

50

100

150

200

250

Anhydrous ammonia

Urea

Upper limit of 95% CI5% of NO

2.5% of NO3

-


2006 IPCC Guidelines for National Greenhouse Gas Inventories. De Klein et al.

Lower limit of 95% CI0.2% of NO

0.05% of NO3

-

Total Direct plus Indirect N2O emissions

Becker, MN

To

tal N

2O

(m

g N

m-2

)

0

50

100

150

200

250

Anhydrous ammonia

Urea

Upper limit of 95% CI5% of NO

2.5% of NO3

-


Quantifying Indirect emissions one of biggest challenges

Fertilizer Placement Effects

Conventional AA Injection

• Slow tractor speed with high fuel use

• 15-18 cm deep band

Conventional “Deep” Applicator

Shallow AA injection

• Faster speed

•10-12 cm deep band

• Improved soil closure

• Less fuel use

New “Shallow/Fast” Applicator

(very few studies)

Fertilizer Placement Effects

Effect of AA Injection Depth on N2O Emissions

Breitenbeck and Bremner, 1986

AA injection depth (cm)

0 5 10 15 20 25 30 35

N2O

em

itte

d i

n 1

56 d

ays

(k

g N

ha

-1)

0

1

2

3

4

5

112 kg N ha-1

225 kg N ha-1

Webster clay loam (no crop)

2009 2010

Effects of AA placement depth on N2O emissions

Becker, MN

N2O

(m

g N

m-2

)

0

50

100

150

200

Deep

Shallow

b

a

b

a

Fujinuma et al., 2011 (submitted.)

WHY ?

Replicating experiment in Lamberton and Rosemount in finer texture soils

Anhydrous Ammonia Placement Effects: Irrigated Corn


1. AA Pre-plant/Sidedress 18 cm 90 / 90

2. AA Pre-plant/Sidedress 12 cm 90 / 90

So

il N

O2

- (g

N g

-1)

AA

Urea

5/21/07 6/4/07 6/18/07 7/2/07

N2O

flu

x (

g N

m-2

h-1

)

Corn field, Rosemount, MN

Elevated Soil Nitrite (NO2-)

Venterea et al. 2010. Soil Sci. Soc. Am. J.

Greater N2O Emissions with Anhydrous Ammonia

Soil Nitrite (NO2-)

N2O flux

Greater N2O Emissions with Anhydrous Ammonia

Aerobic conditions

Soil gas O2 concentration (%)

18.5 19.0 19.5 20.0 20.5

So

il d

ep

th (

cm

)0

10

20

30

40

50

0 2 4 6 8 10

Soil gas N2O concentration (ppm)

23 June 2006, WFPS = 42 %

Corn field, Rosemount, MN

O2 N2O

Laboratory kinetics experiments: N2O production under aerobic conditions

NO2

- added (g N g

-1)

0 10 20 30 40 50

N2O

pro

du

cti

on

(

g N

g-1

h-1

)

0.00

0.01

0.02

0.03

0.04

Non-sterile

-irradiated (5 Mrad)

Venterea, 2007. Global Change Biol.

NO2- added to soil N2O production rate

Biotic

Abiotic

Prod. rate = Kp [NO2-]

NO2- added to soil N2O production rate


Measured Kp

0 2 4 6 8 10 12 14 16

Pre

dic

ted

Kp

0

2

4

6

8

10

12

14

16

R2 = 0.70

Kp = a + b 10

-pH + c C

t + d SOC

N2O Production rate = Kp [NO2-]

Rate coefficient correlated with:

• Acidity (10-pH)

• Total organic carbon (Ct)

• Soluble organic carbon (SOC)



1/T (Kelvin-1

)

0.0032 0.0033 0.0034 0.0035 0.0036

ln K

p

-10

-8

-6

-4

-2

CT soil

NT soil

Forest soil

Ea (kJ mol

-1)

5 % 21 %

66 5671 6085 78

Temperature Sensitivity



Headspace O2 concentration (%)

0 5 10 15 20

Rate

co

eff

icie

nt

(Kp)

Sensitivity to O2

NO2- added


N2O

Pro

duction R

ate



Headspace O2 concentration (%)

0 5 10 15 20

Rate

co

eff

icie

nt

(Kp)

Sensitivity to O2

NO2- added

N2O

Pro

duction R

ate

Nitrifying

bacteria

NO3- added

Denitrifying bacteria

Concentrated Band

NH3/NH4+

NO2- NO3

- AOB

Free ammonia toxicity

NOB

NO2-

N2O

Chemical RXN

with SOM

N2O

Nitrifier

denitrification

Nitrite-driven N2O production


High O2 N2

“Chemo-denitrification”


NO2- + H+ +

Lignins

Humic acids

Phenolics

Aromatics

N2O

Stevenson and Swaby, 1964

Overlooked and

understudied process

“Chemo-denitrification”

Broadcast Banded

Effects of Urea placement on N2O emissions

Engel et al., 2010

N2O

(m

g N

m-2

)

0

100

200

300

400

100 kg N ha-1

200 kg N ha-1


High NO2- Low NO2

-

Banding of Urea


Banding as a beneficial fertilizer management practice

Conserves Nitrogen/ Increases NUE

-Slows nitrification and nitrate leaching

-Limits contact with soil microbes

-Increases root access to N

-Decreases distance from plant to N source

• With banding, it may be possible to have:

-Greater overall NUE

-And greater N2O emissions

• N2O emissions usually are < 3% of applied N.

Malhi et al., 1985. 1991; Yadvinder-Singh et al., 1994

Robertson and Vitousek, 2009


AA(banded)

N Losses (N2O, NO, NO

3

-)

Becker, MN

kg

N h

a-1

0

25

50

75

100

a

b

Urea(broadcast)

Is there an optimum banding intensity or geometry that maximizes NUE and

minimizes N2O emissions ?

Banding as a beneficial fertilizer management practice

Conserves Nitrogen/ Increases NUE

-Slows nitrification and nitrate leaching

-Limits contact with soil microbes

-Increases root access to N

-Decreases distance from plant to N source

Malhi et al., 1985. 1991; Yadvinder-Singh et al., 1994

Robertson and Vitousek, 2009

Modeling nitrite-driven N2O emissions

0 5 10 15 20

Bio

mas

s d

en

sit

y (

cells

g-1

)

105

106

107

Time (d)

0 5 10 15 20

0

50

100

150

200

0

1

2

3

4

NH

4

+,

NO

3- (:

g N

g-1

)

NO

2

- (:

g N

g-1

)

Nitrobacter

NitrosomonasNH

4

+NO

2

-

NO3

-

Time (d)

Biomass dynamics nitrite accumulation

Time

Bio

mass

AOB

NOB

0 5 10 15 20

Bio

mas

s d

en

sit

y (

cells

g-1

)

105

106

107

Time (d)

0 5 10 15 20

0

50

100

150

200

0

1

2

3

4

NH

4

+,

NO

3- (:

g N

g-1

)

NO

2

- (:

g N

g-1

)

Nitrobacter

NitrosomonasNH

4

+NO

2

-

NO3

-

Time (d)

Biomass dynamics nitrite accumulation

Venterea and Rolston, JEQ. 2000

jj

jinhjs

j

j

jdC

CKKB

dt

dB

,

max,

• Model can generate curves of nitrite accumulation

but we can’t predict actual behavior

• Little to no information on toxicity kinetics in soil

• Critical / threshold concentrations ?

• Wastewater treatment kinetic models:

Applicable to soils ?

Two-step Nitrification Model


Diffusion-reaction model: simplified: NO2- is not modeled

])[,( 22

NOOTK

y

CD

yz

CD

zt

CR p

2D gas diffusion

Source term:

Kp

temp

O2

NO2-

Soil nitrite concentration (ug N g-1

)

Lateral distance from row (cm)

0 10 20 30 40 50 60 70

Dep

th (

cm

)

0

10

20

30

40

50

20

40

60

80

100

Days following AA application

0 10 20 30 40 50 60

So

il N

O2

- co

ncen

trati

on

(g

g-1

)

0

50

100

150

200

250

Center of AA band

5 cm from center

15 cm from center

Measured soil NO2-


Distance from row (cm)

0 20 40 60

N2O

flu

x

N2O flux varies with position in row due to 2D effects

Model output

Higher flux

directly

above band


Days following AA application

0 10 20 30 40 50

N2O

flu

x (

g m

-2 h

-1)

0

200

400

600

800

1000

= automated chamber data

= model

Assumes:

All N2O comes from nitrite-driven production

No sink term (no reduction to N2)

Model output

Model versus measured fluxes

(integrated across chamber width)

Concentrated Band

NH3/NH4+

NO2- AOB

Free ammonia toxicity

NOB

NO2-

N2O

Chemical RXN

with SOM

N2O

Nitrifier

denitrification



High O2 N2

NO3-

N2O

Denitrification

in anaerobic

microsites

Tillage Management Effects on N2O Emissions

Does reduced tillage decrease (or increase) N2O emissions ?

Potential for N2O emissions to enhance (or offset) GHG benefits of reduced tillage

Properties affected by long-term tillage mgmt

Bulk density

Water content

Temperature

Inorganic N

Organic carbon

Dissolved organic carbon

Soil structure


Properties affected by long-term tillage mgmt

Bulk density

Water content

Temperature

Inorganic N

Organic carbon

Dissolved organic carbon

Soil structure

NT Greater CT Greater

NT > CT CT > NT

Aulakh et al. 1984

MacKenzie et al. 1998

Ball et al., 1999

Yamulki and Jarvis 2002

Baggs et al., 2003

Koga et al. 2004

Venterea et al., 2005

Rochette et al., 2008

Grageda-Cabrera et al., 2011

Jacinthe and Dick, 1997

Kessavalou et al. 1998

Lemke et al. 1999

Kaharabata et al. 2003

Liu et al., 2005


Ussiri et al., 2009

Halvorson et al., 2010

Omonode et al., 2011

Does reduced tillage decrease (or increase) N2O emissions ?

Potential for N2O emissions to enhance (or offset) GHG benefits of reduced tillage

Anhydrous ammonia

N2O

(m

g N

m-2

)

0

100

200

300

400

500

Conventional tillage (CT)

No tillage (NT)

b

a

CT > NT

Venterea et al. 2005. JEQ.


Anhydrous ammonia Surface broadcast urea

N2O

(m

g N

m-2

)

0

100

200

300

400

500

Conventional tillage (CT)

No tillage (NT)

b

a

b

a

CT > NT NT > CT


Venterea et al. 2005. JEQ.

Vertical Profiles of Potential N2O Production

Venterea and Stanenas. 2008. JEQ.

No-till soil profile

soil surface

High nitrifying activity

High denitrifying activity

Low nitrifying activity

Low denitrifying activity

Depth

(cm

)

0 – 10 cm

Plowed soil profile

soil surface

Depth

(cm

)

Moderate nitrifying activity

Moderate denitrifying activity

0 – 25 cm

Subsurface fertilizer

placement

Minimize N2O emissions

Agrees with tillage-by-placement pattern

(12/18)

Mixed application or no information (5/18)

Disagrees with tillage-by-placement pattern

(1/18)


NT > CT CT > NT

MacKenzie et al. 1998

Ball et al., 1999

Yamulki and Jarvis 2002

Baggs et al., 2003


Grageda-Cabrera et al., 2011

Koga et al. 2004

Rochette et al., 2008

Aulakh et al. 1984

Jacinthe and Dick, 1997

Lemke et al. 1999

Liu et al., 2005


Ussiri et al., 2009

Omonode et al., 2011

Kaharabata et al. 2003

Kessavalou et al. 1998

Halvorson et al., 2010

NT Greater CT Greater

Recommendation for no-till: Subsurface N application, but not AA

Nitrogen Use Efficiency and N2O emissions

Van Groenigen et al. 2010

An elegant idea: N2O emissions will be minimized when NUE is maximized

N surplus (kg N ha-1

)

-150 -100 -50 0 50 100 150

Gro

win

g S

ea

so

n N

2O

em

iss

ion

s Meta-analysis

results:

N2O increased exp.

when N surplus > 0

N surplus = Fertilizer N inputs – above-ground crop N uptake

per

unit o

f cro

p N

upta

ke

Nitrogen Use Efficiency and N2O emissions Nitrogen Use Efficiency and N2O emissions

Van Groenigen et al. 2010

An elegant idea: N2O emissions will be minimized when NUE is maximized

N surplus (kg N ha-1

)

-150 -100 -50 0 50 100 150

Gro

win

g S

ea

so

n N

2O

em

iss

ion

s

Outliers: Low N uptake

NT system in 2 dry years

Meta-analysis

results:

N2O increased exp.

when N surplus > 0

N surplus = Fertilizer N inputs – above-ground crop N uptake

Not clear if this simple relationship is going to hold in the majority of cases

3 years of data,

Rosemount corn

Whole curve shifted down:

Sidedress N application

per

unit o

f cro

p N

upta

ke

Summary & Conclusions

1. In general, we think that any practice that increases NUE would tend to also

minimize N2O emissions – more studies needed to confirm.

e.g. * Split versus single applications

* N rate that is well-matched with yield potential

* Variable rate application where appropriate

* Optimizing other nutrients (P, K, S)

*Also expect these practices to minimize indirect emissions

2. However, it’s not clear if all practices that increase overall NUE will decrease

N2O emissions: Banding ?

3. Some alternative practices that may have the same overall NUE may have

higher N2O emissions:

Depth of placement

Fertilizer source (AA vs. urea)

3. Need more studies looking at these factors.

4. Need better emissions models that account for these factors, because direct

measurement of N2O emissions on farmer’s fields is impractical

Broader Implications / Questions

Optimization of fertilizer management is only part of solution; range of

activities is required:

1. Cover cropping / companion cropping / more diverse rotations to

reduce N requirements and retain more N during non-growing season

2. Restoration of riparian vegetation

3. Edge of field denitrification barriers / bioreactors or controlled drainage

systems to reduce stream nitrate inputs

(current research area, some practices may increase N2O emissions)

Is there any hope of actually decreasing global N2O emissions in light of rising

population and demand for food ?

---With CO2, we have hope that renewable fuels can reduce emissions.

Or is best we can hope for to minimize N2O emissions per unit of production?

What will be long-term effects (GHG and ozone), even if we can minimize

emissions on a yield-scaled basis?

management impacts on nitrous oxide emissions from

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