N Reservoir Biosphere (living organisms) 

 Hydrosphere (water)  Atmosphere (air) 

 Geosphere   

 Crust    Soils and Sediments 

    Mantle and Core  

MegaTons2.8 x 105

2.3 x 107

3.86 x 109

1.636 x 1011

0.13 - 1.4 x 1010

0.35 - 4.0 x 109

1.6 x 1011

% of Total0.0002 0.014 2.3 97.7 

0.78-8.4    0.21-2.4    95.6 

Where is the N on planet earth ??

Most of the N is deep within the earth but very little of this N participates in biological cycles.

Reservoir/Pool Type Biosphere  Hydrosphere  Soil  Atmosphere     

MegaTons2.8 x 105

2.3 x 107

0.35 x 109

3.86 x 109

% of Total     0.0002      0.014      0.21     2.3

Biologically relevant N

% of BR N     <0.01      < 1%      ~ 8 %  > 90 %

N has two stable isotopes, 14N and 15N.14N is much more abundant than 15N

15N labeling can be used to track the fate of added N

Why is N2 so unreactive ???

N2 is chemically unreactive at the temperatures and pressures of the hydrosphere, biosphere, and atmosphere because of its triple bond. This triple bond can only be broken under extreme temperatures and or pressures or in the presence of select enzymes.

Reactive N

Reactive N

Reactive N

Reactive N

~ 5 MT

~ 20 MT

~ 30 MT

~ 85 MT

> 90 MT

Human activities now dominate global cycling of reactive N

Nitrogen has many different oxidation states !

Species   Name Oxidation State

NH3, NH4+   Ammonia, ammonium ion        -3

N2H4 Hydrazine     -2

NH2OH Hydroxylamine     -1

N2 Nitrogen       0

N2O Nitrous oxide     +1

NO  Nitric oxide     +2

HNO2, NO2- Nitrous acid, nitrite ion     +3

NO2 Nitrogen dioxide     +4

HNO3, NO3-    Nitric acid, nitrate ion     +5

Organic N

Well aerated soils

Plant metabolism

Poorly drained soils

Most reduced

Most oxidized

C-NH2

Do any of you remember this view ???

April 19, 1995 - Alfred P. Murrah Federal Building

Nitrate is a powerful oxidizing agent

Ammonium nitrate

+diesel fuel

Why is this combination explosive ?

The on-going process of N shifting from one formto another is collectively called the N cycle

Plant biomass

Plant uptake

SoilM

icro

bial

bio

mas

s

Why do plants need N ?

Nitrogen is an integral component of many essential plant compounds

Amino acids Proteins

Nucleic acidsChlorophyl

enzymes2.5 - 4% of plant dry matter

Old leaves first

Evidence of N Deficiency

yellowing (chlorosis) that starts at the tip and moves in

along the midrib

These symptoms should not be used to identify where N

is needed.

Major irreversible yield loss has

already occurred when these

symptoms are present

Nitrogenase: the key to biological N fixation

Only way that N “fixation” can occur at low temperatures and pressures

Substantial energy input is still required

~ 8 lbs of C per lb of N fixed

Legume nodulescome in

many shapes and sizes

Inoculation groups for commonly grown forage legumes.

Alfalfa Group(Rhizobium meliloti)

AlfalfaBlack medicBur cloverButton cloverWhite sweetcloverYellow sweetclover

Clover Group(Rhizobium trifolii)

Alsike cloverArrowleaf clover*Ball cloverBerseem cloverCrimson cloverHop cloverPersian cloverRed cloverRose clover*Subterranean clover*White clover

Cowpea Group(Bradyrhizobium japonicum spp.)

AlycecloverCowpeaKudzuPeanutLespedezaJoint vetch

Lupine Group(Rhizobium lupini)

Blue lupineWhite lupine

Pea and Vetch Group(Rhizobium leguminosarum)

Bigflower vetchCommon vetchHairy vetchRoughpeaWinter pea

Other** Bird’s-foot trefoil (Rhizobium loti)Cicer milk vetchCrown vetchSainfoin (Rhizobium)Soybean (Rhizobium japonicum)Kura cloverLeucaena

Soybean has its own inoculation group

Amount of nitrogen fixed by various forage legumes

CropN fixed

(lb/A/year)

Alfalfa 150-300+

Red clover 70-200

White clover 75-150

Other annual forage legumes

50-150

Not all legumes are efficient N fixers !

Efficient N fixationforage legumes, soybeanscowpeas, peanuts

Inefficient N fixationsnap beansgarden peaslima beans

NH4+

Nitrification

Nitrification is actually a multi-step process

NO2- is a toxic intermediate product

Warm, aerated, near neutral conditions promote rapid nitrification

NO3- NO2

-

http://www.ipm.iastate.edu/ipm/icm/node/181/print

Sample Date

Dec. 8 Apr. 2 May 3

Application N-serve % NH4-N Remaining

Nov. 7 (>50°F)No 39 19 3

Yes 63 28 17

Nov. 18 (<50°F)No 40 33 7

Yes 57 58 26

http://www.ipm.iastate.edu/ipm/icm/2001/10-22-2001/why50.html

Nitrification inhibitors are not 100% effectiveand are only cost-effective in some situations

NO3-     NO2

-     NO     N2O     N2

Denitrification

Warm, anaerobic conditions + OM promote rapid denitrification

Why is nitrate such a slippery character ?

• Nitrate is an anion• Nitrate compounds are very soluble• Nitrate is next in line as an electron acceptor when O2 is not present

Immobilization

Net

min

eral

izat

ion

Net

im

mo

bil

izat

ion

Jenkinson

Mineralized soil N

wheat pasture

PotentialN uptake by

N is often a limiting nutrient

Where does the N come from ?

Magdoff and Weil (2003)

Well-fertilized crops often obtain more than half of their N from SOM

Why more soil N?

Effect of tillage and crop on mineralizable N

Adapted from Magdoff and Weil (2004)

Mineralizable N declines during grass crops

Mineralizable N increases during soybeans

Sorghum Wheat Soybeans

What happens to fertilizer N ?

http://agronomyday.cropsci.uiuc.edu/2001/tours/n-fate/index.html

Measured after harvest

Environmental losses during

growing season

90

100

80

Which N rate is

likely to result in the most leaching over the winter?

N rates applied to corn in the US have been relatively stable for 3 decades

Corn yields have increased steadily since ~ 1940

160 bu/acre

http://www.fertilizer.org/ifa/publicat/PDF/2005_ag_frankfurt_lammel_slides.pdf

Weather often regulates crop productivity more than nutrient input rates in high productivity systems

lbs

of

gra

in p

er lb

of

N

As a result…Yield per unit of N has increased over the last 30 years

Some farmers consistently harvest more than75 lbs of grain for each lb of N applied

?

Can we manage for the variable amount of N

supplied by soil ?

Why don’t most labs test for N ???

Total soil N is also a poor predictor of in-season availability of N

Preseason mineral N is a poor predictor of in season availability of N in humid regions

Soil organicmatter4000 160 80

200 200

Microbial biomass

NO3- + NH4

+

From the atmosphere 50

To the atmosphere 10-50 ? Fertilizer

Cropuptake

Loss byleaching20-100 ?

PSNT

  Soil yield potential

  Very high/high Medium/low

PSNT value Nitrogen credit

- - ppm N - - - - - lb N/a - - -

> 21

18-20 100 80

15-17 60 80

13-14 35 40

11-12 10 40

< 10 0 0

Nitrogen credits for the pre-sidedress soil nitrate test (PSNT)  

http://ipcm.wisc.edu/WCMNews/tabid/53/EntryID/293/Default.aspx

Benefit from added N is unlikely

http://www.spectrumanalytic.com/support/library/rf/Presidedress_Nitrate_Nitrogen_Test_University_Summary.htm

Researchers in many states have evaluated the PSNT and identified modifications that

work well for specific crops and locations

Click on this hot link:

Comparison of the ISNT and PY methods for predicting sites where corn is nonresponsive to N fertilization.

No. of nonresponsive sites

Sites predicted by

Managementsystem

# of sites studied

total PY ISNT

Manured within 1 year

21 19 6 17

Continuous corn

27 16 0 14

Corn after soybean

49 12 0 11

Corn after alfalfa

6 5 0 5

Corn after wheat

2 0 0 0

Total 105 52 6 47

The 84 sites identified by crop rotation had not received manure for at least three years prior to the growing season studied.

PY = Proven Yield method of determining N rate for corn

Recommended N rate = Proven yield in bushels* 1.2 lbs of N/bushel – manure or legume credits

Illinois Soil N test = Amino sugar test

The soil sample is treated with sodium hydroxide solution in a Mason jar, then heated for five hours on a griddle at 48–50º C to

convert amino sugar-N to gaseous ammonia.

The ammonia is collected in boric acid-indicator solution and determined by titration.

http://cropsci.uiuc.edu/classic/2002/Article9/figure1.cfm

Amino sugar N

No response to additional N

No relationshipbetween ISNT and EONR

University of Wisconsin-Madison Department of Soil Science 2006

Relationship between ISNT and total SOM in Wisconsin

• Strong correlation of ISNT values to soil organic matter (OM) shows that the ISNT is probably measuring a constant fraction of soil organic N rather than a readily mineralizable N pool

Organic matter (%)

0 1 2 3 4 5

ISN

T (

mg

kg

-1)

0

100

200

300

400

y = 12.9715 + 62.5734xr2 = 0.88n = 80

Nitrogen (N) prices and environmental concerns have caused many corn (Zea mays L.) producers and advisors to rethink their current N management practices. These past 3 years, laboratory and field trials were conducted in NY to evaluate the performance of the Illinois Soil N Test (ISNT) in identifying whether or not additional N was needed. Initial test results showed the need for temperature control in the laboratory and resulted in a modification of the procedure to include enclosed boxes. Evaluation of the ability of the modified ISNT procedure in detecting increases in organic N upon compost and manure addition showed an increase in ISNT over time consistent with N credits from manure currently employed for N management in New York. However, to obtain an estimate of potential N release from readily available organic N sources, sampling should not take place within 4-5 weeks after manure (or fertilizers that contain ammonium) application or sod or cover crop plowdown or chemical kill.

Research in NY

Results of the first 3 years of field trials showed that soil samples taken to 20-cm (8 inch) depth and analyzed for both ISNT and LOI-OM can be used to predict the need for additional N for corn beyond starter fertilizer in New York

A & L Great Lakes Laboratories, Inc.3505 Conestoga Dr.Fort Wayne, IN 46808-4413(260) 483-4759http://www.algreatlakes.com

Cropsmith, Inc.107 S. State St.Monticello, IL 61856(217) 621-6117http://www.cropsmith.com

AgVise Laboratories604 Hwy. 15 W.P.O. Box 510Northwood, ND 58267(701) 587-6010http://www.agviselabs.com

Midwest Laboratories13611 B. St.Omaha, NE 68144(402) 334-7770http://www.midwestlabs.com

Spectrum Analytic Inc.PO Box 639Washington Court House, Ohio 43160(740) 335-1562 (Ohio - local)(800) 321-1562 (Toll-Free)http://www.spectrumanalytic.com

VH Consulting, Inc.805 Lund St. N.Hudson, WI 54016(715) 222-3366vhconsul@msn.com

Commercial labs that provide the ISNTThere are several labs in the U.S. which currently run the amino sugar N test as part of their soil analysis services. By listing these labs we offer no endorsement of the

labs. If you have questions about where to get your samples analyzed, please contact us for advice.

www.cropsmith.com

CROPSMITH FAQ

Getting Started With the New Illinois Soil Nitrogen Test

Identify fields for sampling. a. Submit boundary file or plat map b. Sample will be taken on approximately 1.5 acre grids or by management zones. c. Soil samples will be taken from 0-12 inches and 12-24 inches for organic nitrogen analysis.

Submit field history and cropping plan. a. Improving nitrogen management relies on identifying the factors that are important for crop response and developing individual field recommendations. b. Initial rates will be conservative although in many cases may allow for substantial nitrogen savings.

Review nitrogen soil map and application map. a. Apply nitrogen with variable rate applicator. b. Evaluation rates can be included in map so future rates can be adjusted for localized field responses. c. Map yields and analyze evaluation rates.

ISNT map can be used for several corn crops.

Use test strips to adjust to optimum economic nitrogen rate. With previous map as a guide, resample to improve accuracy of organic nitrogen test and to track any changes in test values.

A recent U of I study showed that high plant population is more important for high corn yields than nitrogen fertilizer on productive soils. The reverse was

true on less-productive soils.

The ISNT has been discussed positively and negatively in quite a few farm press articles

over the last several years.

GreenSeeker Technology

High N rate strip needed

6.  How has using GreenSeeker impacted your farming operations? Do you think GreenSeeker saved you money either in cost savings or yield improvement? We were a little conservative with GreenSeeker the first year. We used it on 4,000 acres and reduced nitrogen application about 20 pounds an acre on average. We didn’t lose any yield. You couldn’t tell any yield difference between fields with lower nitrogen applications and our regular program, which averaged about 155 pounds.  We saved at least 20 units across the board. The total nitrogen savings was about $24,000. So I paid for the cost of GreenSeeker the first year.   

7.  What would you tell a fellow farmer who was considering GreenSeeker? You have to trust what you are doing and have faith in the concept. Don’t go hog wild. Maybe only do half your crop the first year. And then you will see whether it will pay for itself. There are a lot of times when you are sidedressing (without GreenSeeker) and the crop doesn’t look like it needs it. The GreenSeeker takes the guesswork out of it. 

8.  Any final thoughts on GreenSeeker. The overall concept behind GreenSeeker will be even more important in the future. If you can save yourself a little bit on each farm, it adds up. 

Even though prices are good now, you still have to farm like your profit potential is poor. That is just good business. The biggest way you can save money is with N. 

If there is a penny to be saved, I am going to save it. Those pennies here and there are what got you through when you were selling your corn for $2. The way nitrogen costs, we can’t afford to waste it. 

Some GreenSeeker results from the IA Soybean Association On-Farm Network

What do you think this rig costs ?

Have any of you ever heard of the Soil Doctor system ?

Relationship between optimal N rate and optimal corn yield in IL (72 site years)

Only 13 out of 72 site-years in IL required more than 1 lb of N per bushel

1 : 1 line

1.2 : 1 line

too high 96% of the time

too high 82% of the time

BOTTOM LINEThere is no line that fits this data well

Yield is a poor predictor of optimal N rate !!

www.extension.iastate.edu/Publications/PM2015.pdf

Price ratio = 0.10

Maximum return to Nwhen price ratio is 0.05

PRICE RATIO

0.20

Less N is needed when corn is planted late

Research at the Northern Illinois Research Center has shown that less nitrogen fertilizer is required for most profitable yield when planting date is delayed.

Based upon that research, U of I agronomists suggest that for each week of delay in planting after the optimal date for an area, the nitrogen rate can be reduced 20 pounds per acre - down to 80 to 90 pounds per acre as the minimum for very late planting in a corn–soybean cropping system.

Suggested reference dates are April 10 to 15 in southern Illinois, April 20 to May 1 in central Illinois, and May 1 to 10 in northern Illinois.

It is better to apply N in the spring – even if a nitrification inhibitor is used

http://soil.scijournals.org/cgi/content/full/68/2/545/FIG4

Soil pH

% N

itri

fica

tio

nImpact of pH and an inhibitor on % nitrification

Inhibitor = N-Serve

Soil pH within the range of 6 to 8 should be considered an important factor affecting the

risks and benefits associated with fall

applications of anhydrous ammonia under climatic conditions found in the Corn Belt.

Relatively rapid nitrification in the higher-pH soils increases the potential for early season losses of

fertilizer N by leaching and denitrification of NO–3

before plants begin rapid growth and uptake of N in June.

Most widely used N fertilizers in IL

Monoammonium phosphate (MAP)

52% P2O5, 11% N, 100% water soluble

Very high phosphorus analysis. Excellent material for use in starter fertilizer

Diammonium phosphate (DAP)

46% P2O5, 18% N, 100% water soluble

Most common phosphorus fertilizer. Used extensively as the basis for blended fertilizers

Ammonium polyphosphateSolid: 55% P2O5, 11% NLiquid: 34% P2O5, 10% N

Liquid form is very common N and P fluid fertilizer

Ammonium phosphates

Nitrogen components of phosphorus (P) fertilizers can also be safely credited if they are spring-applied. Crediting half the N is safer if the P was applied in the fall before growth of a summer crop. Nitrogen components of starter fertilizers and nitrogen applied with herbicides should be included as part of the total intended N rate.

Don’t ignore N in DAP, MAP and starter fertilizer

Many anhydrous ammonia applicators give uneven applications, particularly applicators

with older manifolds.

Manifold outlets across from the intake usually put out higher rates than outlets near the intake.

When an older manifold is used, the most important management practice is to randomize the hoses. This means that a row getting a low rate is more likely to be next to a row getting a

high rate, which will minimize yield loss.

The U of I recommends that no fall N applications be made south

of Highway 16 in Illinois.

Urea should not be broadcast and left on the surface for extended periods.

Missouri research has shown a 14 bu/acre yield penalty in corn (average of 38 experiments, mostly no-till) and a 5 bu/acre yield penalty in wheat (average of 9 experiments) when urea is broadcast and not incorporated.

Recommended methods of applying urea:• Treatment with Agrotain volatilization inhibitor before broadcasting.• Incorporation with tillage (within 3 or 4 days of application).• Incorporation with irrigation (within 3 or 4 days). • Knife injection.

Urea (46-0-0)

UAN (urea-ammonium nitrate) solution (28%–32% N) should not be broadcast on high-residue surfaces.

Missouri research has shown a 25 bu/acre yield penalty when solution is broadcast in no-till corn

(average of 20 experiments, mostly corn-soybean rotation). In tillage systems with less residue, less

yield loss would be expected.

Dribbling solution reduces contact between nitrogen and residue, and

injection is best !

http://frec.cropsci.uiuc.edu/2007/report9/

• EEffectiveffective

• EEfficientfficient

• EEnvironmentally nvironmentally SSmart mart NNitrogenitrogen

http://www.agrium.com/5228.jsp

Do you use any slow release N sources???

YES !> 50% of the N taken up by corn

is normally from OM

Recommended adjustments in N rates for legumes or manure

The cornstalk nitrate test developed by Iowa State University (Iowa State Extension publication PM-1584, Cornstalk Testing to Evaluate Nitrogen Management) is a reliable way to evaluate your N program at or near harvest. It cannot be used to guide N application rate, but can be used to tell whether the N rate in a particular area was too low, optimal or excessive. Feedback gained from this test can help producers improve rate decisions in following years.

So how well did you do ?

Cornstalk nitrate testing

700-2000 ppm = optimum

http://www.extension.iastate.edu/Publications/PM1584.pdf

Recommended N application rates for small grains

Recommended N application rates for grasses