Right ProductWith higher prices for fertilizer nutrients, it becomes more

important to use product s that provide high efficiency. Premiums previously considered unaffordable now become cost-effective. Controlled-release sources, or those with inhibitors slowing down the conversion to nitrate, can more efficiently deliver nutrients to the plant, provided they are applied in situations where their nutrient release matches the uptake needs of the crop.

Are controlled release products better than split applications of 100% available nutrient sources?

Ongoing research is still needed to determine when they are or are not. A split application of soluble fertilizer entails different risks than those associated with a single application of a controlled-release product. The soil may be too wet atside-dress time to get on to the field. Or, in some years, soils may be so dry that side-dressed N—even in fluid form—does not get to the roots. Split applications also entail extra fuel costs.

Controlled-release products can potentially be more reliable and more convenient. But weather and many other soil factors can influence the rate of release, so it’s important to evaluate which product performs best in your own specific growing conditions.

Limited research has been done on these products, so a combination of searching out relevant results and conducting on-farm trials is called for. Price changes may affect some products more than others. Compare price per pound of N in a variety of N sources. Make sure product are suitable for available application equipment.

What are What are enhanced efficiency fertilizers ?efficiency fertilizers ?

Enhanced efficiency fertilizers

• EEF are products with characteristics that minimize the potential of nutrient losses to the environment, as compared to products with 100% availability at the time of application.

• Have traditionally been used in specialty applications (e.g., turf, ornamentals, etc.)

• Over the past few years have been gaining in use and popularity in production agriculture

History of EEFsHistory of EEFsafter Dr. J Robbins, U. of Arkansasafter Dr. J Robbins, U. of Arkansas

• 1924- UF (European patent); 1955 production in the U.S.

• Early 1960’s- crotonylidene diurea

• Late 1960’s- IBDU

• 1961- SCU (TVA); commercial production began in early 1970’s

Fertilizer historyFertilizer historyafter Dr. J Robbins, U. of Arkansasafter Dr. J Robbins, U. of Arkansas

• 1967- Osmocote®

• 1985- Nutricote ® (Meister ®, Prokote ®, Escote ®)

• 1990- Polyon ®

• 1990- Multicote ®

• 1990’s- VCote ®, TR2 ®, ESN ®, Duration ®

Enhanced efficiency NEnhanced efficiency N

• Synthetic organic N compounds with lower solubility – e.g., urea-aldehyde condensation products,

urea-formaldehyde reaction products, IBDU, triazines, etc.

• Physical coating or barrier around soluble N sources– e.g., SCU, PCU, combination products

• Stabilized materials– e.g., nitrification and urease inhibitors

Sulfur Coated UreaSulfur Coated Urea

• Mechanisms of N Release– pin holes, cracks– Microbial degradation

• Factors affecting N release– Coating thickness and uniformity

effective coating thickness is equal to thinnest area of coating

– Temperature– Moisture

Polymer coated ureaPolymer coated urea

• N release controlled by diffusion• Major factors affecting release

– coating thickness– temperature– moisture

N uptake curve (corn) and theoretical PCU N uptake curve (corn) and theoretical PCU release curverelease curve

Schwab and Murdock. 2004.

Comparisons of pre-plant PCU with urea and UAN at equal N rates

0

10

20

30

40

50

-20 -18 -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20

Magnitude of Yield Difference (bu/ac)

Num

ber

of C

ompa

rison

s

Compilation of data from source-rate studies and trials in the US Corn Belt, 2000-2005 - A. Blaylock

247 total Comparisons26% lower yield

71% higher 3% no difference

Lower yield

Higher yield

Impact of urea/UAN and PCU on corn yieldImpact of urea/UAN and PCU on corn yield

50

60

70

80

90

100

Rela

tive C

orn

Yie

ld (%

of m

ax.)

50

60

70

80

90

100

0 40 80 120 160 200 240

N Rate (lbs/acre)

Rela

tive C

orn

Yie

ld (%

of m

ax.)

Urea and UAN

PCU (ESN)

Compilation of data from source-rate studies and trials in the US Corn Belt, 2000-2004 Blaylock and Tindall

More sensitive to unfavorable

weather

Effect of N sources on Effect of N sources on irrigated no-till corn yieldirrigated no-till corn yield

Kansas, Crete silt loamKansas, Crete silt loam

155171

194177

199215

183202 214

0

25

50

75

100

125

150

175

200

225

80 160 240

N applied preplant surface broadcast, lb/A

Co

rn y

ield

, bu

/A

Urea PCU Amm. Nitrate

Gordon. KSU Fertilizer Report. 2006.3-year average

Zero N control- 127 bu/A

Impact of rainfall on corn yield response to ESN vs. Urea

Nitrification…a natural process in soilsNitrification…a natural process in soils

• Nitrification inhibitors interfere with activity of Nitrosomonas bacteria, slowing the nitrification process

• This leaves more N in ammoniacal form, thus reducing the chance of leaching and denitrification

NH4+ NH3 NO2

- NO3-Nitrosomonas Nitrobacter-H+

+H+

Some patented nitrification inhibitorsSome patented nitrification inhibitors

Frye. 2005.

54

95

82

119126

132123

0

25

50

75

100

125

150

0 80 121 161

N rate, lb/A

Co

rn y

ield

, bu

/A

without nitrapyrinwith nitrapyrin

Frye, 2005.Urea or UAN surface applied

Effect of nitrification inhibitor on Effect of nitrification inhibitor on no-till corn yieldno-till corn yield

KentuckyKentucky

Research throughout the Midwest has shown that nitrification inhibitors only pay for themselves environmental conditions favor high losses of nitrate . When inhibitors are applied preceding higher than average rainfall, increases in corn yield range from 10 to 30 bushels per acre; when moisture conditions are normal or dry, nitrification inhibitors produce little to no increase in yield.

In general, poorly or imperfectly drained soils tend to benefit the most from nitrification inhibitors. Moderately well-drained soils that undergo frequent periods of 3 or more days of flooding in the spring also benefit. Coarse-textured soils (sands) are likely to benefit more than soils with finer textures because the coarse-textured soils have a higher potential for leaching.

Urea hydrolysisUrea hydrolysis

• Urease inhibitors interfere with the process of urea hydrolysis

• The slowing of conversion of urea to ammoniacal N can significantly reduce the potential for NH3 volatilization

CO(NH2)2 + H+ + H2O 2NH4+ + CO2

ureaseUREA

Effect of N placement, source, and Effect of N placement, source, and NBPT on irrigated no-till corn yieldNBPT on irrigated no-till corn yield

Kansas, Crete silt loamKansas, Crete silt loam

127

207189

171

212

0

25

50

75

100

125

150

175

200

225

Control UAN- dribble UAN Urea Urea+NBPT

N applied preplant, 160 lb/A

Co

rn y

ield

, bu

/A

Gordon. KSU Fertilizer Report. 2006.2-year average

Broadcast

Apparent N fertilizer recovery in no-till cottonApparent N fertilizer recovery in no-till cottonMississippi, Marietta fslMississippi, Marietta fsl

60.7

40.6

31.3

5.1

21.2

0

10

20

30

40

50

60

70

UAN + NBPT UAN Urea + NBPT Urea A. nitrate

Ap

par

ent

N r

eco

very

, %

Earnest and Varco. 2006.

Surface dribble Broadcast

• Traditional applications– Turf, ornamentals, nurseries, etc.

• Production agriculture – High value crops– Crops with shallow root systems– Where potential for N loss is large (surface

application, sandy soil, high rainfall, etc.)– Environmentally sensitive areas

Enhanced efficiency fertilizer are well suited for:

• Potential benefits of EE fertilizers include: – match the timing of nutrient release with the timing

of plant demand for nutrients– improved yields – Improved nutrient use efficiency– reduction in nutrient loss (leaching, denitrification,

volatilization...)– reduced application frequency– more uniform plant growth

Right Rate

Corn normally shows a diminishing response as the rate of N increases. The economically optimum rate occurs where the yield

increase no longer pays for the last increment of fertilizer. As price ratio increases, the optimum rate decreases.

When prices for both corn and fertilizer increase proportionally, the optimum rate does not change, but the consequences of a non-optimal rate are more costly. It becomes more important to use every means at your disposal to get the best estimate possible of

the optimum rate. For N, this can be difficult.

A pre-sidedress soil nitrate test (PSNT), taken when the corn is 6 to 12” tall, can help guide decisions on sidedress N applications. For an

in-season assessment, a SPAD meter (chlorophyll meter) has proven effective and many universities provide guidance on using it.

For an end-of-season assessment, stalk nitrate tests are recommended.

The N rate that results in

maximum return on

investment decreases as

the price ratio increases.

60 cents / $3 = 0.2030 cents / $6 = 0.05

No fertilizer needed

Readings are taken from the uppermost leaf with the collar visible until the VT stage (tassel emergence), and then from the ear leaf. Average 15-30 representative readings per field location or reference strip location.

Relative Minolta SPAD 502® chlorophyll meter value and N rate to apply.

* Relative values calculated by dividing readings from the area of interest by readings from the well-fertilized reference strip. Readings taken from approximately the V10 to VT corn growth stage.

Relative SPAD Value* N Rate to Applylb N/acre

< 0.88 1000.88-0.92 800.92-0.95 600.95-0.97 30> 0.97 0

High N strip

For nutrients less mobile than N—like P and K—increasing price ratios may also lead to lower “optimal” application rates

Soils with response probabilities less than 50% are often fertilized only for maintenance. Soils where response is very unlikely are often not fertilized at all.

A short-term strategy of reduced application rates when price ratios are high is not likely to reduce yield and may increase profit. However, the consequent decline in soil fertility for future crops needs to be considered.

High price ratios increase the profitability of sound soil testing to identify fields and areas within fields where rates below removal may be justified for one or several years.

Right TimingSpring applications of N are nearly always more effective than fall applications. In IL, ~ 15 % of N applied in the fall is lost but the amount can be much higher. At best, fall applications can only equal the effectiveness associated with spring applications.

Fall applications are made to manage other risks – primarily logistical ones. Fall applications take advantage of typically drier soil conditions and the greater availability of days suitable for field work. They also allow some of the tasks to be moved from a busy spring to a less busy fall, increasing the chances that the spring tasks will be timely. High fertilizer prices tend to favor an investment in equipment to apply N in the spring.

Nitrogen should only be applied in the fall after the average daily soil temperatures at 4 to 6 in. deep (measured mid-morning) go below 50 ºF and are sustained at or below this for the winter. Nitrification inhibitors can increase the effectiveness of fall N.

In Iowa , research with controlled-release urea products (PCU), has found an average 4 bu/A corn yield increase compared to fall-applied urea. However, the fall-applied PCU produced 4 bu/A less yield compared to spring-applied urea which had an 8 bu/A yield advantage for over fall-applied urea.

In the eastern Corn Belt, fall-applied N tends to be more unreliable and inefficient than in IA.

Even when all N is applied in the spring, split applications are normally more effective than single applications of %100 available N sources.

There are two things you can estimate more accurately in June than at planting: one, the soil’s ability to supply N, and two, the crop’s need for N.

While corn doesn’t take up much N during the first month after emergence, it needs a good supply from the start.

Applying some N at planting or pre-plant and a larger dose when corn is > 6” tall normally increases yield and N-use efficiency.

Right Placement

Corn has a special need for P early in the growing season. Placement with the seed in small amounts, and near the seed in larger amounts, provides maximum availability to young seedlings. Applying P in bands below the soil surface reduces the risk of it moving to water by surface runoff and reduces fixation by the soil. Early phosphorus also promotes early dry down which can help lower grain drying expenses.

Research suggests that combinations of N and P work most effectively, and that K is an important component of starter fertilizer for corn grown with reduced or no tillage.

Volatile sources of N should be incorporated or injected! When N sources containing urea or ammonium (urea, urea-ammonium nitrate, anhydrous ammonia, ammonium nitrate, and ammonium sulfate) are surface applied without incorporation, ammonia losses can be high especially when soil pH is high and/or residue levels are high.

Broadcasting UAN solution (28 percent to 32 percent N) is not recommended when residue levels are high because of the potential for the N in the droplets to become tied up on residue. Dribbling the solution in a surface band will reduce tie-up on residue, and knife or coulter injection will eliminate it . Volatilization losses can be minimized by incorporating urea/UAN as soon as possible.

Source: Lowenberg-DeBoer, 1997

0

20

40

60

80

100

1990 1995 2000 2005 2010 2015 2020

Far

m A

do

pti

on

(%

)

Initial Enthusiasm

Discouragement,lack of support,low profitability

Mainstream adoption

Breakthroughallows full adoption

Adoption plateau due to technological or institutional barriers

Source: Lowenberg-DeBoer, 1997

Precision Services Used

0

10

20

30

40

50

60

70

2000 2001 2002 2003

% o

f R

esp

on

den

ts

Precisionservices offered

GPS guidance

Field mapping

GPS-logistics

No services

Midwest dealers use more precision services than other states: 69.2% vs. 43.1%

Whipker & Akridge, 2003

Precision Services Offered

0

10

20

30

40

50

60

70

1997 1998 1999 2000 2001 2002 2003 2004 2005

% o

f R

esp

on

den

ts GP soilsampling

GIS Fieldmapping

GPS Agron.Rec.

Yield Mon.data anal.

SatelliteImagery

Midwest dealers offer significantly more precision services except satellite imagery.

Whipker & Akridge, 2003

Variable Rate Applications

0

10

20

30

40

50

60

1997 1998 1999 2000 2001 2002 2003 2004 2005

% o

f R

esp

on

den

ts Manual

Controller-singlenutrient

Controller-multiplenutrients

Midwest has generally greater than twice the adoption rate of variable rate application compared to other states.

Whipker & Akridge, 2003

Dealer Estimate of Total Market Area Using Precision Services

0

5

10

15

20

25

30

35

40

45

50

2000 2001 2002 2003 2005

% o

f M

ark

et

Are

a

Yield monitor-Midwest

Yield monitor-other states

GPS soilsampling-MidwestGPS soilsampling-otherstatesSatellite imagery-Midwest

Satellite imagery-other states

Whipker & Akridge, 2003

Summary of first 15 years

• Technology has developed rapidly• Scientific basis for explaining and

responding to variability lags behind expectations

• Economics have not met expectations

Economic Analyses of Published Studies

• Results are mixed: – 25% clearly profitable– 25% clearly unprofitable– 50% partially

• Depends on analysis assumptions

Profitability in SSM StudiesCropCrop InputsInputs Grid AreaGrid Area SSM>WFSSM>WF

sugarbeetsugarbeet NN 2.752.75 2/22/2

wheat, wheat, barleybarley

N, P, KN, P, K 3.03.0 1/51/5

corncorn P, KP, K 3.03.0 5/125/12

corn, corn, soybeansoybean

P, KP, K 2.52.5 15/1815/18

irr. cornirr. corn NN 0.750.75 2/42/4

corncorn P, KP, K 2.12.1 5/55/5

Swinton and Lownberg-DeBoer, 1998, J. Prod. Agric. 11(4):439-446