Nitrogen – BMPs for Environmental Quality

Beth Guertal Auburn University, AL

NITROGEN • Fertilizer nutrient added in greatest quantity to

turfgrass. Nutrient that is most likely to be deficient.

• N ranges of 4 to 6% in creeping bentgrass tissue.

• N ranges of 2.5 – 5% in bermudagrass tissue. • Nitrogen is in several amino acids – become

protein and nucleic acids (DNA/RNA). • Also a key part of chlorophyll.

Effects of Nitrogen – Dark Green Color

The Nitrogen Cycle

• N2 gas is 78% of the earth’s atmosphere

• N gas must be converted to plant available forms

• Plants take up nitrate (NO3) and ammonium (NH4) (plus some urea)

N In N Out

Nitrogen Availability in Soils is Complicated Largely driven by a wide range of microbial species which act on the different N forms

How We Add N to the Soil: • Decomposition of organic material – this could

include manures, organic fertilizers, wastes. • Mineralization - process which converts organic N

into plant-available N forms. • Inorganic fertilizers. • N fixation by Rhizobia – specialized relationship with

legumes (symbiotic). • N fixation by other biological processes (non-

symbiotic). • Lightning activity – deposition of nitrate.

How We Add N to the Soil:

Conversion of Organic Matter to Inorganic N:

Organic wastes and residues are converted to plant-available forms of N (nitrate and ammonium) via the process of mineralization. Mineralization is a microbial process. Another process can also occur – called Immobilization, another microbial process where inorganic N is converted to organic N forms.

Organic Matter in Turfgrass Systems – Thatch, Roots, Clippings, Shoots

Where does N go in turfgrass? Days after Canopy N Application

fertilization location Spring Fall

percent of total

18 Clippings 3.1 0**

Verdure 46.7 32.5

Thatch 39.8 56.4*

Soil 10.4 11.1

Leachate 0 0

750 Clippings 55.2 46.9*

Verdure 2.7 0.8

Thatch 20.8 20.9

Soil 21.2 31.1

Leachate 0.04 0.2

Urea applied to Kentucky bluegrass at 0.8 lb N 1,000 ft2 (39.2 kg ha-1)

Miltner et al., 1996

Where does N go? – Part 2 Site Total soil C Total soil N NH4-N NO3-N

mg C g-1 soil mg N g-1 soil

ug g-1 soil

ug g-1 soil

Native pines 25.7 b 0.88 bc 1.5 a 0.0 d

1 to 3-yr turf 8.4 c 0.53 c 0.2 a 8.1 c

6 to 8-yr turf 17.7 bc 1.15 bc 0.1 a 25.6 b

23 to 25-yr turf 27.3 b 1.98 b 0.2 a 24.9 b

95 to 97-yr turf 48.2 a 4.15 a 0.9 a 50.8 a

• Hybrid bermudagrass fairways, Pinehurst area. 0-5 cm sampling depth. • Potential N mineralization in oldest system 3x greater than in youngest

system. • Old turfgrass systems can conserve soil N compared to young.

Adapted from Shi et al., 2006 a and b

The Specifics of Mineralization • Soil microbes use the R-NH2 groups. N is

released as NH4+, which is then oxidized to

NO3.

• About 2 to 3.5% of organic N mineralizes annually (~ 65 kg N ha-1)

R-NH2 - OH- + R-OH + NH4+

ammonification

4H+ + energy + NO2- - energy + NO3

-

nitrification

Ammonification

• The first part of the mineralization process

• It is the conversion of organic N to ammonium

• It is done by a wide variety of heterotrophic organisms – these get their energy from decomposing organic compounds.

• A wide range does this, many groups.

R-NH2 ---- OH- + R-OH + NH4+

Nitrification

• Nitrification is the second step of mineralization

• It has two parts – Part 1: – Ammonium is converted to nitrate by autotrophic

(these get their energy by oxidizing NH4 ions) bacteria.

– Specific group of bacteria – Nitrosomonas

NH4+ + O2 ----- NO2

- + 2H+ + H2O + energy

The NO2 is toxic, so this step happens quickly

Nitrification

• Part 2:

Nitrite is immediately acted on by a second group of autotrophs (called Nitrobacter).

Nitrate is formed.

NO2- + O2 -------- NO3

- + energy

1

2

3

4

5

6

7

8

9

30-Apr 20-May 9-Jun 29-Jun 19-Jul 8-Aug

Urea - 0.5 lb N/M

AS - 0.5 lb N/M

Milorganite - 0.5 lb N/M

Control

Relative Color (1-9 scale) of Hybrid bermudagrass as affected by N source, Auburn, AL, 2009

Rela

tive

Colo

r

Mineralization in a bermudagrass fairway Soil Organic matter Net mineralization Applied N

mg kg-1 kg N ha-1

Rimini (Spodosol) 45 154 132-161

Rimini 27 82 132-161

Norfolk (Ultisol) 34 60 160-213

• 50 and 75 year old fairways. • Soil nitrate-N consistently low (1 – 4 mg kg-1 soil), similar to

natural areas. • The Net mineralization was calculated from a lab study, and it

indicates that from 60 to 154 kg N ha-1 could be released from organic N mineralization (May – October).

Lee et al., 2003

Summary – Mineralization/Immobilization in Turf

• Can have rapid immobilization into thatch/soil.

• However, turnover back into forms for turf uptake can also occur rapidly.

• Older turf systems store organic N, which is a large pool of potentially mineralizable N.

• The bacteria that do this are present in sufficient amounts in the soil.

Nitrification Inhibitors

• In agriculture, we try to slow this ammonium to nitrate conversion using nitrification inhibitors.

• Have been around for 40 years, but are coming back into the market again with new products.

• ‘Stabilized N’ fertilizers

‘Stabilized’ Nitrogen Fertilizers

• Urea with the addition or either a nitrification inhibitor (dicyandiamide), urease inhibitor (N-(n-butyl) thiophosporic triamide), or both.

• Inhibits the enzymes urease and ammonium mono-oxygenase.

• Another product is NutriSphere-N, which is a maleic-itaconic copolymer

Weekly 2M KCl Extractable Soil NH4-N as Affected by N Source

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90

100

1 2 3 4 5 6 7 8 9 10

weeks

soil

NH

4-N

(ug/g

)

ControlUreaUmaxx

Weekly 2M KCl Extractable Soil NO3-N as Affected by N Source

0

10

20

30

40

50

60

70

80

90

1 2 3 4 5 6 7 8 9 10

weeks

soil

NO

3-N

(ug/g

)

ControlUreaUmaxx

Nitrification – Conversion of ammonium into nitrate, done by nitrifying bacteria. Incubation study. Effect of addition of dicyandiamide.

Extractable soil ammonium Extractable soil nitrate

urea

urea

+ inhibitor

+ inhibitor

control control

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3

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5

6

7

8

9

0 10 20 30 40 50 60

rela

tive

colo

r (1-

9 sc

ale)

days after N application

Check

Urea

Urea + Agrotain

SCU

(NH4)2SO4

Fall Color Trials – Started August 29 2007 with N @ 3 lb N/M

Inhibitor

2

3

4

5

6

7

8

9

0 7 14 21 28 35 42 49 56 63 70 77

rela

tive

colo

r (1-

9 sc

ale)

days after fertilizer application

Relative color of Tifway hybrid bermudagrass as affected by N source, Auburn, AL.

Fertilizers applied on May 19th 2008 at 1.5 lb N/M.

Urea

Urea+NSN

Polyon

Control

Fertilizer N from Rainwater?

• Fairhope, AL • Collected rainwater from November 1994

through November 1998 (358 events) • Analyzed for nitrate and ammonia • Only about 18 lbs N per acre per year as

ammonia and nitrate were received in an average of 77.5 inches of rainwater.

• Amount is slightly higher than typical reported values (five to 10 pounds N per acre per year). (0.6 g m-2)

How We Add N to the Soil: • Decomposition of organic material – this could

include manures, organic fertilizers, wastes. • Mineralization - process which converts organic N

into plant-available N forms. • Inorganic fertilizers. • N fixation by Rhizobia – specialized relationship with

legumes (symbiotic). • N fixation by other biological processes (non-

symbiotic). • Lightning activity – deposition of nitrate.

Symbiotic N fixation

Example of Research – Nonsymbiotic N fixers

• greenhouse study • turf-type bermuda, 8 genotypes • inoculated with Azospirillum &

Azotobacter • 0 lb N or 2 lb N/1,000 sq. ft. • no N - top growth increased 17% • with N - no effect • no color or root growth differences

(Baltensperger et al., 1978)

Diazotrophs and N Fixation • do not function in most soils as biological N fixers • there is an exact criteria to convert N2 to ammonia • only in low-maintenance situations - no N fertilization

How N is Added to Soil: Summary

• Fertilization - Y

• Decomposition - Y

• Symbiotic and non-symbiotic N fixation – N

• Atmospheric deposition – y

Ways we can lose N via the N cycle:

• Immobilization – N fixed by microbes into an organic form.

• Volatilization – N lost to atmosphere as ammonia gas.

• Denitrification – N lost to atmosphere as nitrous oxide gases.

• Leaching – N lost to groundwater or out of rooting zone as nitrate-N.

• Fixation – N fixed in layers of some clays. • Plant Uptake – removal of N in disposed clippings

Immobilization • Fixation of plant-available forms of N into organic forms

by microbes. • Immobilized N is not plant available. • Occurs in high-carbon situations – a problem with high

carbon composts, not our turf fertilizers.

• In turf –older soils can accumulate significant organic N (limited research).

Immobilization • KY bluegrass – spring or fall applied N had rapid turf

uptake and immobilization.

• As much as 20% of applied N in soil at any time (over 2 yrs).

• N in thatch ranged from 62% (18 DAT) to 20% (2 yrs).

• After 2 years 38% of the N harvested in clippings.

• N applied in 5 yearly applications of 35 lb N/acre each time.

Miltner et al., 1996

Loss of N to atmosphere as ammonia gas. Big issue in manure application. Common with urea or urea-based products. Irrigation lowers N loss.

Lab Method

Volatilization

Ammonia Volatilization Over 10 Days Laboratory Study

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5

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35

40

urea SCU polymercoated urea

methyleneurea

AN compostedsewagesludge

control

N Source

% N

Vol

atili

zed

A

BBB

B

B

Passive Micrometerological Technique – Field Study

Wind vane

10 foot aluminum mast

Oxalic acid-coated tubes inserted perpendicular to mast at 5 heights

Ammonia Volatilization Over 10 Days Field - Spring 2006

Time (days)

mg-

N v

olat

ilize

d

0

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4

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16

1 2 3 4 5 6 7 8 9 10

Polymer coated urea Methylene Urea

Urea

Total Ammonia Loss as a % of total N Applied – Field Study

0

5

10

15

20

25

30

FA 05 SP 06 FA 06

% N

Vol

atili

zed

urea

MU

PCU

M

U

MU

urea

urea

PCU

PCU

N volatilization as affected by N source, 1 gram urea applied

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5

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25

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35

40

1 3 5 7 10 14 20Days after experiment start

N v

olat

ilized

as

a pr

ecen

tage

of N

app

lied

Urea + AgrotainUreaBare Soil

Ammonia volatilization as affected by N source and inhibitor

Inhibitor

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0 1 2 3 4 5 6 7 8 9 10

N v

olat

ilize

d as

a p

erce

nt o

f N a

pplie

d

weeks after N application

Ammonia Volatilization as affected by N source, 10 week field study. N applied at 1.5 lb N/M on July 20 2009.

Urea

Polyon

XCU

Umaxx Urea + Inhibitor

Denitrification

2NO3 - 2NO2- - 2NOg -- N2O g -- N2 g

This is a series of biochemical reactions caused by a wide variety of heterotrophic anaerobic bacteria.

Occurs with < 10% oxygen.

Optimal temperature 25-35C.

Major areas of N loss via denitrification

• Rice paddies

• Wetlands

• Heavily fertilized or manured soils

• Automobile exhausts

• Manure storage

To be exact: Nitrous oxide – N2O (also comes from nitrification) Nitrogen oxides – NO + NO2

Denitrification Soil Type Soil Temp C (F) Soil water

content (% saturated)

Percent of N applied lost

silt 22 (72) 75 0.02

26 (79) 75 0.07

30 (86) 75 0.11

30 (86) 100 94

35 (95) 100 91

silt loam 30 (86) 100 46

35 (95) 100 41

• Kentucky bluegrass, two soil types • Maximum losses occurred quickly – within 5 days

Mancino et al., 1988

Denitrification • N2 and N2O losses from KY bluegrass or creeping

bentgrass ranged from 2.5 to 11.2% (21 d total) • KNO3 treatment had greater denitrification than urea

treatment. • Denitrification loss occurred even when standing

water was present. Horgan et al., 2002

• Over a year, from 0.65 to 2.02% of applied N lost as N2O-N. • N fertilization did increase emissions within 3 days (as

compared to unfertilized) , especially when significant precipitation occurred.

Bremer, 2006

Leaching

• Loss of N out of root zone as the mobile cation nitrate.

• We care because: 1) we lose plant-available N, and, 2) there are some negative public health effects.

• Avoid over-application and overwatering, esp. in sandy soils.

‘Minnesotans have a chance to get water tested for nitrates’

Greer and Shannon, PEDIATRICS Vol. 116 No. 3 September 2005

Nitrate in Groundwater:

‘Infants for whom formula may be prepared with well water remain a high-risk group for nitrate poisoning. This clinical report reinforces the need for testing of well water for nitrate content’.

‘A 1950 report listed 144 cases of infant methemoglobinemia with 14 deaths in one 30-month period in Minnesota. Infant deaths resulting from misdiagnosis of this preventable, treatable intoxication were still occurring as recently as 1986 in South Dakota. In this state, about 39% of dug or bored wells were unsafe due to high nitrate content, compared with 22% of drilled wells and 16% of driven wells. Properly constructed wells more than 30 m deep are more likely to be safe’.

Johnson and Kross, Am J Ind Med. 1990;18(4):449-56

Nitrate in leachate as affected by N source, applied (3 lb N/M) on June 30th, Auburn, AL

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10000

20000

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80000

2-Jul 16-Jul 30-Jul 13-Aug 27-Aug 10-Sep 24-Sep

date of sampling

Nitr

ate

in le

acha

te (u

g)

ScottsTB

Urea

UAN

Leaching • Loss of N out of root zone as nitrate. • We care because: 1) we lose plant-available N, and, 2) there are some

negative public health effects. • Avoid over-application and overwatering, esp. in sandy soils.

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0 7 14 21 28 35 42 49 56 63 70

NO

3-N

(ug)

days after fertilization

Cumulative nitrate in leachate - sand

Control Polyon Umaxx Urea

Urea + Inhibitor

Nitrate-N in leachate – Marvyn loamy sand - 2009

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0 7 14 21 28 35 42 49 56 63 70 77 84

days after fertilization

Cumulative nitrate in leachate - Marvyn loamy sand

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0 7 14 21 28 35 42 49 56 63 70 77 84

NO

3-N

(ug/

mL)

days after fertilization

Leachate Nitrate (weekly collection) - Marvyn loamy sand

Control

Polyon

Umaxx

Urea

Urea + inhibitor

NO

3-N (ug)

• Michigan lysimeter project – started 1989

• KY bluegrass, 3 inch mow height

• 1998-2002: N at 2.0 or 5.0 lb N 1,000 ft-2 yr-1

• In 2003 high N rate reduced to 4.0 lb N 1,000 ft-2 yr-1

Long-term turfgrass leaching work

All work Kevin Frank, MSU

Long-term turfgrass leaching work

As a turfgrass manager, which loss paths really matter?

• Leaching – environmental concerns, watch for loss of N in sand-based soils, avoid overwatering.

•Volatilization – irrigate surface-applied urea sources to prevent. Possible use of stabilized or slow-release products. Other n sources, too.

•Denitrification – we simply do not know. Unless soils are completely saturated we don’t seem to have an issue.

• Immobilization – not yet shown to be a big factor in turf, not a day-to-day issue. In older turf mineralization-immobilization often reach a balance.

Effects of Nitrogen – Vigorous Vegetative Growth

y = 0.8x2 - 3.92x + 88.1R² = 0.9933

83

83.5

84

84.5

85

85.5

86

86.5

0.5 1 1.5 2

Nm

lbs N 1,000 ft-2 month

Torque reading of established Tifway bermudagrass as affected by N rate, June 2003

Effects of Nitrogen – Vegetative Growth Effect of N Rate on Dry Root Mass of TifEagle Bermudagrass

1/16

1/8 1/4

1/2

1.0

0.01

0.015

0.02

0.025

0 1 2 3 4 5

N rate (g N m -2 week -1 )

Mas

s of

Dry

Roo

ts (g

)

1/16 lb N

1/4

1/2

1 lb N

Applying more than ½ lb N/1,000 sq. ft/wk (for grow-in) decreased dry root weight.

1.81.9

22.12.22.32.42.52.62.7

0.5 1 1.5 2

Wei

ght (

g)

N Rate (lbsN/1000ft2/week)

Effects of Nitrogen – Vegetative Growth Effects of N rate on the dry weight of stolons and rhizomes – Tifway and TifSport hybrid bermudagrass

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32

0 1 2 3 4 5

Sept, 2003

March, 2004

N Rate (g m-2 wk-1)

1/8

1/4

1/2

1

1/16

TNC

(g k

g-1)

Fall and spring carbohydrate content as affected by N rate. TifEagle.

Effects of Nitrogen – Carbohydrate Storage

Thank You!