Managing Reactive N in 

the Environment

C.S. Snyder, PhD, CCA

Nitrogen Program Director

Presented to 

EPA FRRCC 2009
Food riots in Haiti over high prices for 

rice, beans and other food staples led to 

the ouster of the government on Saturday.
IPNI is committed to a healthy 

and adequate global food supply
EPA SAB Integrated Nitrogen 

Committee Report on Reactive N (Nr)

November 15, 2008

• Improved practices -impact lowered through better management 

practices

• Product substitution - a product is developed or promoted which 

has a lower dependency on, or releases less, reactive nitrogen) 

• Transformation - one form of N converted to another form

• Source limitation - introduction of Nr in environment lowered 

through preventive measures (e.g. precision fertilizer application, 

controls on NOx generation)

• Removal - in which Nr is sequestered from impacting a particular 

resource

• Improved use or reuse efficiency - efficiency of production that is 

dependent on Nr is improved (e.g. increased grain yields for lower 

Nr applied), or Nr wasted from one source is reused in another (e.g. 

algal farming).

From DRAFT report Nov. 15, 2008
EPA INC Draft Recommends - Reduce 

Nr Loss to Environment by 25%

• Decrease livestock-derived ammonia 

emissions to approximately 80% of 1990

• Decrease excess flows of Nr into streams, 

rivers, and coastal systems by approx. 20%

• Increase crop output while reducing total 

Nr up to 20% of applied artificial Nr.

• High priority for a targeted construction 

grants program under the CWA (i.e 

wetlands)

From DRAFT report Nov. 15, 2008

Galloway & Cowling, 2002; UNEP, 2003
The Nitrogen Cycle

Atmospheric

nitrogen

Atmospheric

fixation 

and deposition

Animal

manures

and biosolids

Industrial fixation

(commercial fertilizers) Crop 

harvest

Volatilization

Denitrification

Runoff and

erosion

Leaching

Organic

nitrogen

Ammonium

(NH4)

Nitrate

(NO3)

Plant 

residues

Biological

fixation by

legume plants Plant

uptake

Input to soil Component Loss from soil

-

+
EPA Hypoxia SAB report suggested 

45% less total N 

AND

45% less total P

discharge to the Gulf to reduce 

hypoxia
Notable

Declines

Has nutrient discharge increased ?
Discharge by 5 Major Sub-basins

Where is it coming from?

16 61 84 74 64
USGS Estimates Loss of N and P to 

Water Resources in Different Areas

SPARROW - Modeled Estimate of N and P

Discharge in Watersheds of the Mississippi R. Basin

kg/ha

.01 

.01- 0.1

0.1 to 1

1 to 5

5 to 10

>10

kg/ha

.001 

.001- 0.01

0.01 to 0.1

0.1 to 0.5

0.5-1.0

>1

Alexander et al. Environ. Sci. Technol. 2008, 42, 822–830
Sub-basin Contributions of N & P 
Voluntary actions 

are reducing the 

“net” Nitrogen (N) 

balance in the 

Mississippi River 

Basin; especially 

in two key upper 

sub-basins.
Voluntary actions are 

also reducing the 

“net” phosphorus (P) 

balance in the 

Mississippi River 

Basin; especially in 

two key upper subbasins.

This is a concern, 

however, because soil 

P may be “mined”, 

and may lead to yield 

reductions and lower 

N use efficiency
60

80

100

120

140

160

180

200

0 20 40 60 80 100 120 140 160 180 200

N rate, lb/A

with P

without P

Effect of N and P on Corn Yield

Schlegel, Dhuyvetter, and Havlin, 1996

J. Produc. Agric. 9:1

30 year average

N rate at max yield:

with P = 167 lb/A

without P = 161

P increased N use 

efficiency instead of 

greatly increasing 

N fertilizer demand
0

50

100

150

200

0 40 80 120 160 200

N rate, lb/A

S

oil N

O

3

-

N in

u

p

p

e

r

1

0

f

t, lb

/

A

with P

without P

P Reduces Residual Soil Nitrate and 

Potential for Nitrate Leaching

At optimum N rate 

P reduced residual 

nitrate by 66%

Schlegel, Dhuyvetter, and Havlin, 1996

J. Produc. Agric. 9:1

30 year average
0.75

0.66

0.47

0.33

0

0.2

0.4

0.6

0.8

0-0-0-0 300-0-0-0 300-100-0-0 300-100-80-0 300-100-80-40

N-P-K-S, kg/ha

A

p

p

a

r

e

nt N

r

e

c

o

v

e

ry

e

fficie

n

c

y

Arrows are % increase in apparent N 

relative efficiency over previous treatment

Gordon. Better Crops. 2005 (KS, Car sandy loam) Assumes uptake 1.4 lb N/bu grain 

2- year average (2001- 2002)

--- 41 % 40 % 14 %

Balanced Fertilization Improves

Crop N Recovery
Percent of soil samples requiring 

annual P fertilization to avoid profit 

loss in most major crops in 2005

Fixen et al. 2006

Summary of 3.4 million

soil samples for 2005 

growing season
Percent of soil samples requiring 

annual K fertilization to avoid profit 

loss in most major crops in 2005

Fixen et al. 2006

Summary of 3.4 million

soil samples for 2005 

growing season
Decadal-Scale Changes of Nitrate in Ground 

Water of the United States, 1988–2004. 

(Rupert. 2008. J. Environ. Qual. 37:S-240–S-248)

• 67% of sites (16 out of 24) -

had no significant change in 

NO3 concentrations

– All but 1 of the 8 others had 

increases in NO3

• “A subset of wells had data 

on ground water recharge 

date; nitrate concentrations 

increased in response to the 

increase of N fertilizer use 

since about 1950.”
NO3

-N loads Total N loads

Rebich and Remchek, 2007

Scientific Investigations 

Report 2007–5090

“Notable increasing trends in nitrite plus nitrate and total 

nitrogen at selected study sites were attributed to both 

point and nonpoint sources.”
Kitchen and Goulding (2001) in

Nitrogen in the Environment: Sources, 

Problems and Management

• “ nitrogen use efficiency

...rarely exceeds 70% ....... 

often ranges from 30-60%”

• “conversion of N inputs to 

products for arable crops can 

be 60-70% or even more”
We can improve Nutrient Use 

Efficiency & Effectiveness

by implementing

Fertilizer BMPs .....

right source @ right rate @right time

& right placement

4R Stewardship
Improving Fertilizer N Use 

Efficiency (NUE)

• Proper rates and sources - best placement and 

proper timing

• Nitrification inhibitors - slow the conversion of NH4

+

to NO3

-

• Urease inhibitors – slow conversion to NH4

+ and 

reduce potential NH3 volatilization

• Slow release N fertilizers - release N over the 

growing season, matching availability and crop needs

• Site-specific applications

– Variable rate, and possibly variable source

– In-season sensing and variable rate/place 

application
http://www.ipni.net/ipniweb/portal.nsf/0/d58a3c2deca9d7378525731e006066d5/$FILE/Revised%20NUE%20update.pdf

How Do You Define and Rate NUE?
NUE Term Calculation Reported Examples

PFP - Partial 

factor productivity

Y/F 40 to 80 units of cereal grain per unit of N

AE - Agronomic 

Efficiency

(Y-Y0)/F 10 to 30 units of cereal grain per unit of N

PNB - Partial 

nutrient balance 

(removal to use 

ratio)

UH/F 0 to > 1.0 - depends on native soil fertility 

and fertility maintenance objectives

<1 in nutrient deficient systems (fertility improvement)

>1 in nutrient surplus systems (under replacement)

Slightly less than 1 to 1 (system sustainability)

RE – Recovery 

efficiency of 

applied nutrient

(U-U0)/F 0.1 to 0.3 - proportion of P input recovered first year

0.5 to 0.9 - proportion of P input recovered by crops in 

long-term cropping systems

0.3 to 0.5 - N recovery in cereals-typical

0.5 to 0.8 - N recovery in cereals- best management

F-amt. nutrient applied, Y- yield of harvested portion with applied nutrient, Y0- yield of harvested portion with no 

applied nutrient, UH –nutrient content of harvested portion of crop, U –total nutrient uptake in aboveground 

biomass with nutrient applied, U0 –total nutrient uptake in aboveground biomass with no nutrient applied 
0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1.4

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

b

u

p

e

r lb

o

f

N

Corn grain produced in the U.S. per unit 

of fertilizer N used, 1964 to 2005.

0.76

1.15

51% increase in N efficiency

12% increase in N fertilizer use Since 1975: 

*

*Application rate for 2004 estimated as avg of 2003 & 2005.

Data sources: USDA Ag Chem Use Survey & Annual Crop Production. 

No USDA survey data for 

2004, 2006, 2007, 2008

(EPA draft U.S. GHG inventory, 1990-2007)
N2O Emissions Trends: Ag Soil 

Management and Total Ag Sector 

(EPA draft U.S. GHG inventory, 1990-2007)

“Annual N2O emissions from agricultural soils fluctuated between 1990 

and 2007, although overall emissions were 1.2. percent lower in 2007 than 

in 1990.N2O emissions from this source have not shown any significant 

long-term trend, as they are highly sensitive to the amount of N applied to 

soils, which has not changed significantly over the time-period, and to 

weather patterns and crop type.”
U.S. GHG Emissions & N2O from

the Ag Sector – CO2 Equiv.

(EPA draft U.S. GHG inventory, 1990-2007)

5.5%

5.6%

5.3% 4.5% 4.7% 4.5%

Ag sector N2O as portion of total US. GHG emissions
U.S. GHG Emissions & N2O from

Ag Soil Management – CO2 Equiv.

(EPA draft U.S. GHG inventory, 1990-2007)

3.6%

3.6%

3.6% 3.1% 3.2% 3.1%

Ag soil mgmt. N2O as portion of total US. GHG emissions
http://www.fertilizer.org

http://www.ipni.net/bettercrops

New IPNI Practical Guide:

Fertilizer Nitrogen BMPs to Limit Losses 

that Contribute to Global Warming



• N source, rate, placement , and 

timing .... which may include

– Urease inhibitors

– Nitrification inhibitors

– Slow-release materials

– Controlled-release materials

• In combination with appropriate, sitespecific cropping system and 

conservation practices 

– (e.g. conservation tillage, cover crops, 

vegetative buffers, managed drainage, 

wetlands, bioreactors, etc.)

• Fertilizer N BMPs can help minimize 

the potential for residual NO3-N 

accumulation & losses
Intensified Fertilizer BMP 

Education & Outreach
New Tools, Technologies, 

Opportunities ??

• John Deere - hi-speed (10 mph) 

anhydrous ammonia applicator

• Agrotain & Lange-Stegmann -

$20 million Urea and 

Stabilized Nitrogen 

Center in St. Louis, MO

• Corn hybrids with improved N 

uptake/redistribution 

characteristics ???
www.ipni.net

Better Crops, Better Environment ... through Science

Thank You