Right Product
With 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 at
side-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 onfarm 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 enhanced
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 EEFs
after 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 history
after 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 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 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 urea
• N release controlled by diffusion
• Major factors affecting release
– coating thickness
– temperature
– moisture
N uptake curve (corn) and theoretical PCU
release curve
Schwab and Murdock. 2004.
Comparisons of pre-plant PCU
with urea and UAN at equal N rates
Compilation of data from source-rate studies and trials
in the US Corn Belt, 2000-2005 - A. Blaylock
Number of Comparisons
50
40
30
Lower
yield
247 total Comparisons
26% lower yield
71% higher
3% no difference
Higher
yield
20
10
0
-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)
Relative Corn Yield (% of max.)
Impact of urea/UAN and PCU on corn yield
100
90
More sensitive
to unfavorable
weather
80
70
Urea and UAN
60
Relative Corn Yield (% of max.)
50
100
90
80
70
PCU (ESN)
60
50
0
40
80
120
160
200
240
N Rate (lbs/acre)
Compilation of data from source-rate studies and trials in the US Corn Belt, 2000-2004
Blaylock and Tindall
Effect of N sources on
irrigated no-till corn yield
Kansas, Crete silt loam
Urea
PCU
Amm. Nitrate
225
200
Zero N control- 127 bu/A
Corn yield, bu/A
175
150
125
100
177
75
155
183
199
202
215
194
171
50
25
0
80
160
240
N applied preplant surface broadcast, lb/A
Gordon. KSU Fertilizer Report. 2006.
3-year average
214
Impact of rainfall on corn yield response
to ESN vs. Urea
Nitrification…a natural process in soils
NH4+
-H+
+H+
NH3
Nitrosomonas
NO2-
Nitrobacter
NO3-
• 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
Some patented nitrification inhibitors
Frye. 2005.
Effect of nitrification inhibitor on
no-till corn yield
Kentucky
150
Corn yield, bu/A
125
without nitrapyrin
with nitrapyrin
132
126
119
123
95
100
82
75
54
50
25
0
0
80
121
N rate, lb/A
Frye, 2005.
Urea or UAN surface applied
161
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 welldrained 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 hydrolysis
UREA
CO(NH2)2 +
H+ +
H2O
urease
2NH4+ + CO2
• 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
Effect of N placement, source, and
NBPT on irrigated no-till corn yield
Kansas, Crete silt loam
225
200
Corn yield, bu/A
175
150
125
207
100
189
75
212
171
127
50
25
0
Control
UAN- dribble
UAN
Urea
Broadcast
N applied preplant, 160 lb/A
Gordon. KSU Fertilizer Report. 2006.
2-year average
Urea+NBPT
Apparent N fertilizer recovery in no-till cotton
Mississippi, Marietta fsl
70
Apparent N recovery, %
60
50
40
60.7
30
40.6
20
31.3
21.2
10
5.1
0
UAN + NBPT
Surface dribble
Earnest and Varco. 2006.
UAN
Urea + NBPT
Urea
Broadcast
A. nitrate
Enhanced efficiency fertilizer are well suited for:
• 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
• 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 nonoptimal 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 = 0.20
30 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 SPAD Value*
< 0.88
0.88-0.92
N Rate to Apply
lb N/acre
100
80
0.92-0.95
0.95-0.97
> 0.97
60
30
0
* 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.
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 Timing
Spring 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 springapplied 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, ureaammonium 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 tieup 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
Farm Adoption (%)
100
Adoption plateau due to
technological or institutional barriers
80
60
Discouragement,
lack of support,
low profitability
40
Breakthrough
allows full adoption
Initial
Enthusiasm
20
Mainstream adoption
0
1990
1995
2000
Source: Lowenberg-DeBoer, 1997
2005
2010
2015
2020
Precision Services Used
% of Respondents
70
Precision
services offered
GPS guidance
60
50
40
Field mapping
30
20
GPS-logistics
10
No services
0
2000
2001
2002
2003
Midwest dealers use more precision services than other states:
69.2% vs. 43.1%
Whipker & Akridge, 2003
Precision Services Offered
% of Respondents
70
GP soil
sampling
GIS Field
mapping
60
50
40
20
GPS Agron.
Rec.
Yield Mon.
data anal.
10
Satellite
Imagery
30
0
1997 1998 1999 2000 2001 2002 2003 2004 2005
Midwest dealers offer significantly more precision
services except satellite imagery.
Whipker & Akridge, 2003
Variable Rate Applications
% of Respondents
60
50
Manual
40
30
20
10
Controllersingle
nutrient
Controllermultiple
nutrients
0
1997 1998 1999 2000 2001 2002 2003 2004 2005
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
50
Yield monitorMidwest
% of Market Area
45
40
Yield monitorother states
35
30
GPS soil
samplingMidwest
GPS soil
sampling-other
states
Satellite imageryMidwest
25
20
15
10
5
Satellite imageryother states
0
2000
2001
2002
2003
2005
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 Studies
Crop
sugarbeet
wheat,
barley
corn
corn,
soybean
irr. corn
corn
Inputs
N
N, P, K
Grid Area
2.75
3.0
SSM>WF
2/2
1/5
P, K
P, K
3.0
2.5
5/12
15/18
N
0.75
2/4
P, K
2.1
5/5
Swinton and Lownberg-DeBoer, 1998, J. Prod. Agric. 11(4):439-446