ammonia volatilization from urea: how large is the issue ... · summary of ammonia loss from uan...

Ammonia Volatilization from

Urea: How large is the issue

and losses.

David E. Kissel

University of Georgia

Overview

• Urea Consumption

• Definitions

• UAN Solution Reactions

• Urea Dissolution and Diffusion

• Urea Hydrolysis

• Ammonia Volatilization

• Research Results

• Summary

Urea

Ammonium nitrate

Nitrogen solutions

Ammonium phosphate

Total compound N

0

1973 / 74

2004 / 05

10 20 30 40 50

www.fertilizer.org

51%

World Evolution of N Fertilizer

Consumption

Millions of tonnes

Urea

Ammonium nitrate

Nitrogen solutions

Total compound N

0

1973 / 74

2004 / 05

1 2 3 4 5

www.fertilizer.org

21%

Millions of tonnes

USA Evolution of N Fertilizer

Consumption

Anhydrous ammonia

Overview


• Definitions



• Urea Hydrolysis



• Summary

Definitions• Dissolution: urea absorbs water

and converts from solid to liquid

• Hydrolysis: urea converts to ammonium (NH4

+)

• Diffusion: movement due to motion of molecules

– Urea has no charge, diffuses easily

– NH4+ has charge, diffuses slowly

Overview


• Definitions



• Urea Hydrolysis



• Summary

Q. Does any ammonia volatilize

from UAN solutions before they are

applied or during the application?

A. None or very little, depending on

if a small amount of ammonia is

added to protect against corrosion of

mild steel.

Composition of UAN 28% N

• 14 % N from Ammonium Nitrate

– 7% ammonium N

– 7% nitrate N

• 14% N from Urea

• 30% water

• + small amounts of inhibitors to inhibit

corrosion of mild steel

Inhibitors to protect against

corrosion of mild steel

• 0.5 % ammonia (raises pH to about 7.5)

• Ammonium phosphates at 0.2 % P2O5

• Others

NH4 NH4 = NH3 + H

+NH4 = NH3 + H

+NH4 = NH3 + H+NH4+ = NH3 + H

+

(ion) (gas)

Urea Hydrolysis in UAN?

• DOES NOT OCCUR

– Therefore no ammonia is formed from the urea

portion of the UAN solution from this process.

– Therefore no ammonia loss from the urea

portion of UAN solution before soil

application.

Summary of ammonia loss from

UAN

• Urea in UAN does not hydrolyze in the fertilizer tank.

• The NH4+ from the ammonium nitrate

portion of the UAN cannot be lost as NH3.• The amount of NH3 added to some UAN to

inhibit corrosion is very small, around 10 lb per ton. A small portion of this NH3 may be lost during application.

Overview


• Definitions



• Urea Hydrolysis



• Summary

Urea Dissolution

• Urea has to be dissolved before it can be hydrolyzed

Urea Dissolution


• Urea can absorb water from the atmosphere and from the soil/crop residue

Urea Dissolution



• Absorption of water from the atmosphere depends on relative humidity (RH)

Urea Dissolution



• Absorption of water from the atmosphere depends on relative humidity (RH)

• Critical relative humidity (CRH) is the RH at which urea dissolves

Effect of Temperature on CRH

and Water Solubility of Urea

Air Temperature (oF)

20 40 60 80 100 120Critical R

ela

tive H

um

idity f

or

Ure

a (

%)

60

65

70

75

80

85

90

Ure

a S

olu

bili

ty (

lb/g

allo

n o

f w

ate

r)

4

6

8

10

12

14

16

CRH

Solubility

Urea Urea UreaUrea Urea Urea

RH > CRH (80%)

Crop residue

Urea dissolution

and diffusion

Dry Soil

www.agrium.com

Urea Urea Urea

Urea dissolution

and diffusion

Urea Urea UreaCrop residue

Urea Urea Urea

www.agrium.com

1/2 inch

Wet Soil

Urea Diffusion into Soil (after 10 days)Urea Concentration in Soil (ppm)

0 100 200 300 400 500 600 700

Soil

Depth

(m

m)

0

10

20

30

40

50

Drier

Wetter

Urea Urea UreaUrea Urea UreaCrop residue

Urea Urea Urea2 inches

Overview


• Definitions



• Urea Hydrolysis



• Summary

Urea Hydrolysis

Urea 2 Urease enzyme

+ H+2 NH4+

• Urease is derived from crop residues

and soil microorganisms

Urea Urea UreaUrea Urea Urea

Crop residue

Urease inhibitor

Urea Urea Urea

Overview


• Definitions



• Urea Hydrolysis



• Summary

(aq)

Soil solution

NH4+

NH3 Volatilization Process

Urea

Atmosphere

Clay

OM

NH4+

NH4+

NH4+

Hydrolysis

NH4+

(aq)+

Equilibrium

NH3 H+

(gas)

Soil air

NH3

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

+ 2 H+ 2

Soil pH

5 6 7 8 9

NH

3 (

as %

of

To

tal A

mm

on

iaca

l N

)

0

5

10

15

20

25

30

68oF

Effect of soil pH on NH3 as % of Total N

(aq)

Soil solution

NH4+

NH3 Volatilization Process

Urea

Atmosphere

Clay

OM

NH4+

NH4+

NH4+

Hydrolysis

NH4+

(aq)+

Equilibrium

NH3 H+

(gas)

Soil air

NH3

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

+ H+

Ferguson et al. (1984)

Days Since Urea Application

0 2 4 6 8 10 12

So

il p

H

6

7

8

9

NH

3 L

oss (

kg

N h

a-1

)

0

4

8

12

High Buffering Capacity

Low Buffering Capacity

Low Buffering Capacity

High Buffering Capacity

•Increase in soil pH

depends on soil H+

buffering capacity

•Higher clay and OM

contents lead to higher

soil H+ buffering

capacity

Atmosphere

H+

H+H+

H+

H+

H+

H+

NH4+

Urea

Urea

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

NH4+

Urea

½ inch

pH 6 7 8 9

NH4+NH4

+

NH4+NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

CECH+

Urea

Urea hydrolyzes on the soil surface

H+

H+

H+H+

H+

H+

H+

H+

NH4+

Urea Urea

Urea

NH4+

NH4+NH4

+

NH4+

Urea

2 inches

pH 6 7

NH4+NH4

+

NH4+

NH4+NH4+

NH4+NH4+NH4

+NH4+

NH3

Urea Urea

Urea

Urea

CEC

Urea hydrolyzes below the soil surface

Soil

+

Effect of Temperature on NH3 Volatilization

NH4+Urea NH3 H+

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

½ inch

Temperature

Effect of Temperature on Urea Hydrolysis

Temperature (oF)

30 40 50 60 70 80 90 100 110

Rela

tive U

rease A

ctivity

0

1

2

3

4

5

6

Gould et al. (1973)

Soil

+


NH4+Urea NH3 H+

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

½ inch

Temperature

Temperature (oF)

30 40 50 60 70 80 90 100 110

NH

3 (

as %

of

Tota

l A

mm

onia

cal N

)

0

5

10

15

20

25

30

35

Effect of Temperature on % of NH3

pH = 8.5

Soil

+


NH4+Urea NH3 H+

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

½ inch

Temperature

Temperature (oF)

30 40 50 60 70 80 90 100 110Rela

tive D

rivin

g F

orc

e for

Convers

ion

of A

queous N

H3 to G

aseous N

H3

1

2

3

4

5

Effect of Temperature on Conversion of

Aqueous NH3 to Gaseous NH3

Soil

+


NH4+Urea NH3 H+

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

½ inch

Temperature

Soil

Wind speed

+

Effect of Wind Speed on NH3 Volatilization

NH4+Urea

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

NH3 H+

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

Atmosphere

½ inch

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

Am

monia

Loss (

% o

f A

pplie

d N

)

0

5

10

15

20UAN UREA Nitamin

51mm

Replication II0

5

10

15

20 UAN UREA Nitamin

51mm

Replication I

Days After Application

0 20 40 60 80 100 1200

5

10

15

20UAN UREA Nitamin

51mm

Replication III Time00:00:00 08:00:00 16:00:00 00:00:00

Win

d S

pe

ed

(m

s-1

)

0

1

2

3

4

5

High

Low

Time

00:00:00 08:00:00 16:00:00 00:00:00

Win

d S

pe

ed

(m

s-1

)

0

1

2

3

4

5

High

Low

Optimum Conditions for

Volatilization

• Small diffusion depth into soil

• RH > CRH

• High temperature

• High wind speed

• Low pH buffering capacity

Overview


• Definitions



• Urea Hydrolysis



• Summary

Urea Applied to Pasture - Fall 2004

Days after application

NH

3lo

ss (

% o

f applie

d N

)

0

10

20

30

40

50

0.1

0.2

0.3

0.4

10

20

30

40

50

Soil

wa

ter

conte

nt

(g g

-1)

20 40 60 80 100 120

Rain

fall

(mm

)

Nitamin®

UAN

Urea

Rainfall

Soil water content

Temp = 47oF


NH

3lo

ss (

% o

f applie

d N

)

0

10

20

30

40

50

10

20

30

40

50 Nitamin®

UAN

Urea

0.1

0.2

0.3

0.4

Soil

wa

ter

conte

nt

(g g

-1)

20 40 60

Rain

fall

(mm

)

Rainfall

Soil water content

Temp = 63oF

Urea Applied to Pasture – Spring 2005

UreaNH4+

Atmosphere

Clay

OM

NH3

Urea Urea Urea

Urea UreaNH4+

NH4+

(aq)+

Equilibrium

NH4+

(aq)NH3 H+


NH

3lo

ss (

% o

f applie

d N

)

0

10

20

30

40

50

10

20

30

40

50Nitamin®

UAN

Urea

Rainfall

Soil water content

0.1

0.2

0.3

0.4

Soil

wa

ter

conte

nt

(g g

-1)

20 40 60

Rain

fall

(mm

)Temp = 62oF

Urea Applied to Pasture - Fall 2005

Time of RH above CRH in the first 30 d

Tim

e o

f R

H >

CR

H (

h)

0

5

10

15

20

25

0 5 10 15 20 25 30

Total: RH > CRH =19 days63 %


Urea Urea Urea

Atmosphere

Urea Urea Urea

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

Soil water content (0.07 g g-1)

RH > CRH (80%)

Permanent wilting point (0.04 g g-1)

Fescue thatch

NH4+

NH4+

NH4+

NH4+NH4

+NH4+NH4

+


NH

3lo

ss (

% o

f applie

d N

)

0

10

20

30

40

50

10

20

30

40

50Nitamin®

UAN

Urea

0.1

0.2

0.3

0.4

Soil

wa

ter

conte

nt

(g g

-1)

20 40 80

Rain

fall

(mm

)

60

Rainfall

Soil water content

Temp = 69oF

Urea Applied to Pasture – Spring 2006

Urea Urea Urea

Urea Urea UreaNH4+

Atmosphere

NH4+

NH4+

(aq)+

Equilibrium

NH4+

(aq)NH3 H+

NH3

NH3 NH3

NH3

NH3

NH3NH3

NH3

Soil water content (0.15 g g-1)

Field capacity (0.18 g g-1)CEC

Ammonia volatilization losses under field conditions

Fertilizer

--------------- Ammonia loss (% of applied N) -----------------

Fall 2004

Urea

UAN

Nitamin®

19 a*

6 b

6 b

Spring 2005

12 a

13 a

14 a

•Within a column, values followed by the same letter are not significantly different according to

Fisher’s LSD at p=0.05

Summary of Pasture Results

Fall 2005 Spring 2006

46 a

33 b

34 b

24 a

18 a

18 a

Summary for Pastures/No-Till

Dry Soil, Dry Residue, RH < CRH: OK

Dry Soil, Dry Residue, RH > CRH: not OK

Wet Soil, Wet Residue: not OK

• Apply on dry soil, dry residue, expected low RH, and

hope for 1 inch of rain whenever it rains.

• Apply on wet soil if 1 inch rain/irrigation is expected.

Summary for Clean-Till Crops

Dry Soil: OK

Wet Soil: not OK

• Apply on dry soil and hope for 1 inch of rain whenever

it rains.

• Apply on wet soil if 1 inch of rain/irrigation is expected.

Summary for Pastures/CropsKnifed or disked in

Dribbled

Broadcast

• Knifed or disked in better than Dribbled

• Dribbled better than Broadcast

Laboratory Results (77oF, 90% RH)

NH3 volatilization in the lab

Days after application0 10 20 30

NH

3Lo

ss (

% o

f A

pplie

d N

)

0

10

20

30 Urea

UAN

Nitamin®

a

bb

Some Results from Central Great

Plains, Manhattan, Kansas

Topdress N on Wheat

Kansas State Univ., NE KS

N, pounds/acre N Source Yield, Bu/acre

0 45.3

30 Urea 60.2

60 Urea 68.1

90 Urea 71.0

30 Amm. Nitrate 59.1



Ammonia loss from N uptake by

Coastal Bermudagrass- Temple, TX

Bill Hargrove – 1975, 1976

Treatment N rate, pound/A NH3 Loss (%)

Urea 100 0

Urea 200 0

Urea 400 3

UAN 100 8

UAN 200 2

UAN 400 0

Questions?

ammonia volatilization from urea: how large is the issue ... · summary of ammonia loss from uan...

Documents