1. Fertilizer Recommendation
Philosophies
Richard B. Ferguson
University of Nebraska

2. Fertilizer Recommendation
Philosophies
Philosophy - style of
management.
Relates to what type of risk the
producer is most comfortable
with.
Applies to non-mobile nutrients,
primarily phosphorus and
potassium, to a lesser extent
calcium and magnesium.

3. Soil pH Levels
Percent testing 6.0 or less.
Source: P.E. Fixen - Potash Phosphate Institute
Better Crops, No. 4, 1998

4. Soil Test P Levels
Percent testing medium or lower.
Source: P.E. Fixen - Potash Phosphate Institute
Better Crops, No. 4, 1998

5. Soil Test K Levels
Percent testing medium or lower.
Source: P.E. Fixen - Potash Phosphate Institute
Better Crops, No. 4, 1998

6. What is a “Medium” soil test level?
What is a “Critical Level”?
15 ppm
pm
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“Medium” test is
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UNL Categories
VH
“Critical Level”- is the
Test Category
H
soil test value above
which fertilizer is not M
recommended because
there is not a L
significant likelihood
VL
of yield increase. The 0 5 10 15 20 25 30 35 40 45 50
value depends on the Bray-1 P (ppm)
crop.

7. Fertilizer Recommendation
Philosophies
Deficiency Correction
Nutrient Removal
Maintenance
Build
Cation Balance

8. Soil Tests -
Are an index - they estimate
plant availability of nutrients
under field conditions – not
the total amount of nutrient
in the soil.

9. Types of Risk - Fertilizer
Application
Deficiency Correction - Intended to optimize profit.
The risk is that in some years, or some locations
within fields, nutrient supply may limit yield.
Maintenance - Intended to minimize potential for
nutrient limitations to yield. The risk is that, in
most years, no yield increase will occur with the
last increments of fertilizer, thus reducing profit,
and that environmentally excessive rates may be
applied in some locations of the field.

10. Question:
Should fertilizer be applied
at rates adequate to take
advantage of higher yield
potential in years with
exceptional climatic
conditions?

11. Answer:
In most cases, when climatic conditions
favor exceptional yields, they also favor
above-average availability of soil-derived
nutrients. Consequently there is no need to
fertilize above calibrated rates in order to
realize full yield potential in exceptional
years.

12. NSFP 2002 – Yield Response to Selected Treatments
300
5
5 9
9 11
11 12
12 12
12 13
13 14
14 17
17 20
20 20
20 49
49 74 Bray-1 P
74 Bray-1 P
(ppm)
(ppm)
250
200
150
N2P0K1
N2P0K1
100 N2P1K1
N2P1K1
N4P2K2
N4P2K2
50 UNL
UNL
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13. Fertilizing the Crop
Fertilizing the Soil

14. Fertilizing the Soil
Soil is a very inefficient location to store
fertilizer. Crop recovery of fertilizer P, for
example, is typically less than 30% in the
year of application, and less than 10% the
following year. Fertilizer orthophosphate is
converted to increasingly less soluble forms
of calcium phosphate with time, reducing
the availability of applied P to plants.

15. Deficiency Correction
Results from research on crop response to
additions of a nutrient otherwise insufficient
for maximum growth.
Relies on correlation and calibration field
research.
Goal of applying fertilizer P or K to
optimize economic return in the year of
application.

16. Soil Test Research
Correlation - Determination of crop yield
at different soil test levels for a given
nutrient.
Calibration - How much fertilizer is
required to optimize yield at different
soil test levels.

17. Maintenance & Build
Maintenance implies that maintaining a soil test
level at or above the point of economic maximum
yield benefits the producer over time.
Build implies that fertilizer added beyond crop
removal rates to increase soil test levels over time
will be beneficial.
The most likely use for this approach is when soil
nutrient levels are very low and long-term land
tenure is assured.

18. Maintenance & Build
Assume approximately 18 lb/acre of P2O5 is
required to raise Bray-1 P test 1 ppm; 24-27
lb/acre to raise Olsen P test 1 ppm.
Assume 9-10 lb/acre K2O is required to
increase soil K test 1 ppm.

19. Yield Response as Influenced by Soil Test Level
Yield Response as Influenced by Soil Test Level
and Recommendation Philosophy
and Recommendation Philosophy
Economic
Maximum Yield
100
75
Critical Level
% Yield
50
25
Deficiency Correction
Maintenance/
crop removal
Maintenance & Build
0
VL L M H VH
Soil Test Level

20. Crop Removal
Ultimately, over the long-term, both deficiency
correction and maintenance & build
recommendation programs will gravitate towards
replacing the nutrients removed in yield.
Fertilization according to crop nutrient removal
is not likely to be as profitable as deficiency
correction in the short-term.
Land tenure is a major factor influencing one’s
choice of fertilizer program.

21. Cation Balance
Suggests there is an optimum ratio of basic
cations and that there is a best total base
saturation for each soil.
“Ideal” ratio: Ca - 65%, Mg - 10%, K - 5%,
H - 20%.
Initially developed in New Jersey, further
researched in Missouri.

22. Cations required to increase saturation of exchangeable Ca,
Mg and K to the mid-point of a desired range.
Soil CEC = 15 meq/100 g Soil pH: 5.6
Actual Saturation Desired Desired Nutrient
meq/100 g (%) Saturation meq/100 g Required
(%)
4.3
Ca 6.00 40.0 75.0 11.25 tons/acre
ag-lime
Mg 1.50 10.0 10.0 1.50 None
390 lb/acre
K 0.24 1.6 3.5 0.53 0-0-60

23. Cation Balance
Soils have been shown to have wide ranges
of cation ratios and still be highly
productive.
Approach has no validity for soils with pH’s
above 7, but is often used for
recommending K and Mg anyway.

24. How do different
philosophies, or strategies,
of fertilizer
recommendation compare
in yield or profitability?

25. University of Nebraska
Comparison Study
Primary objective - To scientifically
compare fertilizer recommendation
strategies for a range of Nebraska soils.
Conducted at five locations across the state
- continued for up to 10 years at each
location.

26. UNL Comparison Study
Location North Platte Clay Center Mead Concord
Yield 170 bu/a 170 – 200 bu/a 170 bu/a 90 bu/a
Goal Corn Corn Corn Corn
Strategy MB DC MB DC MB DC MB DC
Fertilizer
$/acre 54 26 56 30 62 35 27 12
Yield
Bu/acre 167 167 186 189 152 154 83 84
MB - Maintenance + Build.
DC - Deficiency Correction.
Average cost and yield over 7 years.

27. “The University of Nebraska didn’t
recommend any phosphorus for my field,
and yet I had a 15 bushel per acre yield
increase when I applied 50 lb per acre on
the east half, compared to the west half
where I applied only nitrogen.”

28. Why?
Spatial variability of nutrient levels,
combined with inadequate soil sampling,
may be a major factor in differences in
perception of fertilizer recommendations.
Personal observation or testimonials may
not reflect valid comparisons.

29. Treatment Comparison
Split-field designs to
compare treatments
are basically invalid.
There is no way to
measure random error.
Comparison of
treatments must occur in
a replicated, randomized
manner.

30. Summary
Recommendation philosophies, or strategies,
apply primarily to P and K in Nebraska, to a lesser
extent Ca, Mg, S and micronutrients.
The type of risk the producer is most comfortable
with will influence his fertilizer management
strategy.
The deficiency correction approach has been
shown through research to have the greatest short-
term profitability in Nebraska.

31. Exercise P2O5/acre
2 5
Deficiency Crop
Bray P bu/a Correction Removal
For the 11 yr. period shown,
For the 11 yr. period shown, 12 2002 245
calculate the annual recommended
calculate the annual recommended
P22O55/acre rates using two
P O /acre rates using two
2003 252
approaches: deficiency correction
approaches: deficiency correction
and crop removal. Calculate the
2004 215
and crop removal. Calculate the
total P22O55 applied, the average
total P O applied, the average 2005 196
annual rate, and the total fertilizer
annual rate, and the total fertilizer
cost over the 11 year period.
cost over the 11 year period. 9 2005 205
Assume crop removal to be 0.33
Assume crop removal to be 0.33
lb P22O55/bu.
lb P O /bu.
2007 188
2008 243
2009 216
5 2010 199
2011 238
2012 224
Total P2O5
Total P2O5
Annual mean
Annual mean
P cost (@ $.30/lb)
P cost (@ $.30/lb)

32. Exercise
Bray P bu/a P2O5/a
DC CR
12 2002 245 40 81
2003 252 40 83
2004 215 40 80
2005 196 40 65
9 2005 205 40 68
2007 188 40 62
2008 243 40 80
2009 216 40 71
5 2010 199 80 66
2011 238 80 79
2012 224 80 74
Total P 560 809
Annual mean 51 74
P cost (@ $.30/lb) $168 $243