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not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
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site maintained by the Florida
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Copyright 2005, Board of Trustees, University
SRaz- EFFECTIVE AND ECONOMICAL FERTILIZER CONSIDERATIONS
Charles A. Conover .
Agricultural Research Center Apopka -.
ARC-A Research Report RH-80-3
Extensive research has been conducted on fertilizer sources and
types available to producers. Of particular interest to''producers '-. -
are (1) does the fertilizer grow good quality plants, (2) is the fertilizer
efficient, i.e., are most of the active ingredients such as nitrogen
available to plants, and (3) is the fertilizer economical in cost per unit
of fertilizer, labor required for application and capital investment in
equipment. No single fertilizer source rates highest in all categories.
Additionally, area of use (greenhouse, shade structures or outdoors),
temperature range, potting media, chemical and physical characteristics
and crop turnover all influence the selection of a fertilizer source.
Results Obtained from Various Fertilizer Sources Nearly 10 years of
research on foliage plants with numerous fertilizer sources has shown that
many are acceptable, but that several are most efficient in terms of growth
and quality. Comparisons between fertilizer sources can only be made when
at least nitrogen is applied at similar levels. Plant response depends on
availability of nutrients applied as well as the period of release for slow
release sources. Table 1 provides an indication of fertilizer efficiency
for a number of sources used at the Agricultural Research Center, Apopka.
As shown in the table, it takes 1.33 pounds (sometimes more) of a urea
formaldehyde based fertilizer to get the same response as 1 pound of a
liquid fertilizer of the same analysis. Some of the reasons for this are
that not all of the nutrients are released from slow release sources and
also as foliage plants normally grow rapidly they require nutrients be
available rapidly, as needed.
Fertilizer ratios are also important, but, experimentally, we have not
found any difference between 1:1:1, 2:1:1 or 3:1:2 ratios. However, use of
potassium at less than 66 percent or phosphorus at less than 33 percent of
the nitrogen level is not recommended, as deficiencies may occur.
Table 1. Relative efficiency of several fertilizer sources based on plant
response observed under experimental conditions.
Frequency of Apparentz Lbs needed for
Fertilizer source application efficiency equal response
Liquid Weekly 100 1.00
Dry (100% water soluble) Weekly 100 1.00
Slow release (Osmocote) Quarterly 90 1.13
Slow release (Sulphur-coated-urea) Quarterly 90 1.13
Slow release (Urea Formaldehyde) Quarterly 75 1.33
ZPlant response to liquid fertilizer has been higher than other sources, and
it has been assigned an apparent efficiency of 100 however, actual ef-
ficiency is less.
Professor and Center Director, Agricultural Research Center, IFAS, University
of Florida, Route 3 Box 580, Apopka, FL 32703.
Application of Fertilizers Method of fertilizer application
influences costs associated with a fertilizer program. Several of the more
common methods are discussed here, but others can also be considered. For
the purpose of this discussion, fertilizer costs are based on annual
application costs per acre, but can easily be converted to 1000 square feet
by dividing by 43.6. Table 2 provides an estimate of equipment costs for
applying different fertilizer sources, while Table 3 provides estimates for
Table 2. Estimated equipment
fertilizer to one acre.
needs and costs for various systems of applying
Method of Equipment Initial Annual maintenance Total
application needed cost depreciation cost (annual)
Liquid Tank injector $3000 $300 $300 $600
Dry placed Mix tank 2500 250 250 500
in solution injector
Slow release Storage 800 80 80 160
placed in mixer
Slow release Applicator
directly to storage 1200 120 120 240
pots. .. .
Table 3. Estimated labor costs for applying different types of fertilizer in
Different ways to one acre.
Fertilizer Labor Hours Annual Annual
source cost/hr required/A/wk cost/A/yr cost/TOOOft2/yr
Liquid $5.00 1 $ 260. $ 6.00
Dry (100% soluble) 5.00 3 780 18.00
Dry (mix own) 5.00 4 1040 24.00
Slow release 4.00 0.5 104 2.40
(mixed in medium)
_Slow release 4.00 1 208 4.77
Liquid Application from
is used from a storage tank,
fertilizer lines. Therefore,
associated plumbing (Table 2)
fertilizer and among the lowe
a Storage Tank When concentrated fertilizer
an injector must be used to place it in the
costs include the storage tank, injector and
.This is probably the easiest way to apply
st in labor costs (Table 3).
Liquid Application from a Mix Tank When soluble dry fertilizers are
placed in solution a tank is necessary, so fertilizer can be solubilized with
water to form the desired concentration. Fertilizer solutions can then be
applied with an injector or siphoned into the irrigation system (Table 2).
Once the fertilizer is in a liquid form, it can be applied in numerous ways.
These include overhead application through an irrigation system or by hand,
use of leader tubes, spray stakes, seep tubes laid across containers or on
a capillary mat. Labor costs are higher than for liquid fertilizer, as time
is involved in weighing and mixing solution.
Dry Applications Mixed into Potting Mixture If slow release
fertilizer can be mixed into the potting mixture, it can save some labor
application costs for the first 3-month period (Table 3). However, not
only must the correct amount be incorporated, but also the release rate must
be calculated so the next application can be made at the proper time. The
second application, as well as any additional ones, must be made to the
potting mixture surface. However, if turnover is-rapid, no additional
applications may be necessary.
Dry Applications Applied to the Potting Mixture Surface Slow release
materials can be applied to containers by hand or with several different
types of applicators carried by an individual. Another method is to
broadcast over containers, placed pot to pot, or over stock beds. Equipment
costs are relatively small with either of these systems and storage space
more expensive than the actual equipment (Table 2). Labor costs for
application of slow release fertilizers are among the lowest (Table 3).
Fertilizer Costs Actual cost of fertilizers varies considerably within
even a local area, as well as throughout the United States. Prices listed in
Table 4 are for 1-ton lots purchased from standard supply sources. It is
easy to change the fertilizer cost in the tables that follow to reflect
prices in your area and to obtain costs associated with your type of
operation. When calculating fertilizer costs, one must consider not only the
cost per ton but also cost per unit of fertilizer as well as associated
equipment and labor costs of application. When one combines the relative
fertilizer efficiency data from Table 1, equipment costs from Table 2, method
of application in Table 3 and fertilizer cost information from Table 4, one
can analyze which systems are most cost efficient. One way of making such a
comparison is to select a specific fertilizer rate and then compare total
costs for the different fertilizer sources. For example, if a crop required
the equivalent of 1500 pounds of nitrogen per acre per year and it was applied
to an entire acre (broadcast application), the results would be as shown:
Example #T Using a 9-3-6 liquid fertilizer source, apply 1500 pounds nitrogen
per acre per year to a foliage crop.
A. From Table 1, efficiency factor = 1.00,
B. From Table 2, annual equipment cost for liquid = $600 per acre per
C. From Table 3, annual labor cost for liquid = $ 260 per acre per
D. From Table 4, using liquid source No. 1, nitrogen costs 78 cents
E. Multiply efficiency factor in A (1.00) times pounds of nitrogen
needed (1500) to obtain actual number of pounds needed -
1 x 1500 = 1500,
F. Multiply nitrogen cost per pound from "D" (.78) times actual
number of pounds needed (found in "E"). This provides annual
fertilizer cost per acre. .78 x 1500 = $1170.00.
G. Add annual equipment cost for liquid from Table 2 to "F" above,
as well as annual labor cost for liquid from Table 3. This
provides annual fertilizer and application costs.
$600 + $260 + $1170 = $2030.00
To obtain annual cost per 1000 square feet, divide $2030 by 43.6 = $46.56.
Example #2 Using a 18-6-12 slow release Urea Formaldehyde base fertilizer
source, apply 1500 pounds of nitrogen per acre per year to a foliage crop
by surface application.
A = 1.33
B = $240.
C = $208.
D = $105 per pound
E = 1.33 x 1500 = 1995.00
F = $1.05 x 1995.00= $2094.75
G = $240 + $208 + $2094.75 = $2542.75 per acre per year or $58.32
per 1000 square feet per year.
Table 4. Approximate fertilizer cost per ton and/lb N for several fertilizer
Fertilizer Source Manufacturer Cost/ton Cost/lb Nigrogen
-3-6 USS Agri Chemicals $ 140.51 $ .78
16-4-8z USS Agri Chemicals 194.29 .61
Dry (100% soluble)
20-20-204 Robert B. Peters Co.,Inc. 860.00 2.15
20-10-15 Mixed from NH4NO3, HP04 357.41 .89
Slow Release (Osmocote)
19-6-10 Sierra Chemical Co. 960.00 2.53
14-14-14 Sierra Chemical Co. 1026.00 3.66
Slow Release (Sulphur Coated)
14-14-14z Atlantic Fertilizer Co. 330.00 1.18
Slow Release (Urea Formaldehyde)
25-10-10 The O. M. Scott & Sons Co. 840.00 1.68
18-6-12 Atlantic Fertilizer Co. 380.00 1.05
A quick reference to several sources is listed in Table 5. These data
are calculated as outlined in the examples provided above.
Table 5. Fertilizer costs ($) when 1500 lb N/A/yr is obtained
sources and applied broadcast or placed within containers.
(1000 6" pots)
Dry (100% sol
USS Agri Chemicals
USS Agri Chemicals
Robert B. Peters Co. Inc.
Mixed from NH4N03, HP04 & KNO3
Sierra Chemical Co.
Sierra Chemical Co.
Atlantic Fertilizer Co.
The O.M. Scott & Sons Co.
Atlantic Fertilizer Co.
ZThis calculation can be obtained by solving for an unknown or multiplying the
figure in column A by .195 percent.
The economic data in Table 5 are self-explanatory. However, several
comments can be made:
1. Broadcast application of liquid or dry soluble fertilizer is much
more expensive than in pot application. In addition, when either is applied
broadcast, the actual amount of fertilizer being applied to the pot surface
can vary because of deflection by the plant canopy. This deflection may be as
high as 50 percent with some types of plants. Another problem with broadcast
application is the large amount of fertilizer that does not reach the pot and
runs. off. Energy considerations alone will limit this application method in
2. Pot applications of liquid or soluble fertilizers can be as expensive
as slow release forms placed in the container. It all depends on which materials
3. Consideration has not been given to inclusion of micronutrients in the
fertilizer program. The problem here is that just because a fertilizer source
contains micronutrients, they are not always present in the proper ratio or
quantity. Several fertilizer sources listed that do contain some micronutrients
also required the addition of others or inclusion of another micronutrient
supplement in the potting medium. It is estimated that lack of micronutrients
or the need to supply additional ones will add 10 percent to the total fertilizer