The publications in this collection do
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
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
Techniques of Diluting Solution
Fertilizers in Commercial
Nurseries and Greenhouses
Thomas H. Yeager and Richard W. Henley
AUG 31 1987
University of Florida
For Commercial Use Only U
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences
University of Florida / John T. Woeste, Dean
/ May 1987
Techniques of Diluting Solution Fertilizers
in Commercial Nurseries and Greenhouses
Thomas H. Yeager and Richard W. Henley*
Application of fertilizer in the irrigation water (fer-
tigation) has been a common practice for many years in
the floriculture industry. The use of fertigation in the
woody ornamental industry has increased during the
past decade. Fertigation allows manipulation of plant
nutrition by using different fertilizers containing
equal ratios of nutrients, and adjustment of specific fer-
tilizer elements within a fertilization program.
Changes in the nutrition can be made quickly with
Similar adjustments are difficult or impossible with
slow-release fertilizer products. Fertilizer injected into
irrigation water can be purchased as a solution or for-
mulated by dissolving water-soluble fertilizers. Solu-
tion fertilizers, those with all components dissolved in
water, are generally less expensive than granular fer-
tilizers. Purchased solutions also reduce labor inputs
per application since dry soluble fertilizers must be
dissolved before injection.
Concentrated fertilizer solutions, either purchased
as solutions or formulated by dissolving soluble fer-
tilizers, must be diluted before application. Three
major systems are used to apply the final dilution to
crops: 1) final dilution tank and pump; 2) proportional
fertilizer injectors; and 3) positive displacement fer-
tilizer pumps (nonproportioning).
Final Dilution Tank and Pump Technique
Large tanks, usually of several hundred gallons, are
used to dilute fertilizer to the desired concentration
before application. The tanks are usually constructed
on a concrete slab with concrete block sides and sealed
inside the tank to prevent leakage and deterioration of
the mortar joints. The large, bulky tank and pump
system lacks versatility when nutritional program
changes are needed in different sections of a nursery.
Small portable dilution tanks, up to approximately
200 gallons, are more versatile than large tanks;
however, maximum versatility can be achieved with
irrigation design. The smaller tanks can be designed to
agitate the solution by returning a portion of the
pumped solution to the tank.
Several companies manufacture centrifugal pumps
that resist corrosive solutions and are suitable for
*Extension Ornamental Horticulturist, University of Florida,
Institute of Food and Agricultural Sciences.
pumping dilute fertilizer solution from tanks. The
final dilution tank and pump technique of fertigation
reduces errors, provided the proper amount of fertilizer
is added to the tank initially. However, dilution tanks
are inefficient because irrigation water must be
handled twice, once to dilute the fertilizer in the tank
and a second time to distribute it to the plants.
Proportional Fertilizer Injectors
Three operating categories of proportional injectors
are 1) pressure differential injectors, 2) water motor-
operated injectors and 3) water meter-operated in-
Differential Pressure Injection
When the pressure at the point of injection is less
than that of the intake, concentrated fertilizer will be
pulled into the irrigation water. This can be ac-
complished by connecting a hose to the suction side of
the irrigation pump, and the other end, equipped with
a strainer, is placed in the concentrated fertilizer solu-
tion. An adjustable valve in the hose, or a series of
valves, can be used to adjust the quantity of fertilizer
drawn from the concentrated fertilizer solution,
thereby changing the concentration in the irrigation
The concentration of elements in the irrigation
water must be determined and valves adjusted until
correct fertilizer concentrations are obtained. Once
correct concentrations are obtained, the conductivity
(soluble salts) of the irrigation water should also be
recorded for future use as a guide to proper injection. A
soluble salts measurement does not indicate the level
or ratio of specific salts in the water, nor does it reflect
dissolved, nonhydrolyzed urea. If urea fertilizers are
used, always record soluble salts of the irrigation
water at approximately the same time interval after
mixing the concentrated fertilizer solution.
There are disadvantages with this system. The in-
jected fertilizer concentration can be altered by
changes in pump speed or line pressure causedby leaks
and clogged nozzles and valves. These problems em-
phasize the need to monitor the nutrient levels of ir-
rigation water. Also, if air enters the stock fertilizer
Gainesville, and Extension Foliage Specialist, Apopka AREC,
suction line, the pump will probably have to be primed.
Venturi-type proportioners operate similarly in that
a pressure differential causes concentrated fertilizer to
flow into the irrigation water. As water flows through
a constriction in the proportioner, the water speed in-
creases and pressure decreases. A tube attached at the
constriction facilitates movement of fertilizer from the
concentrated solution into the irrigation water. The
Siphon Mixer* shown in Fig. 1 uses the venturi princi-
ple and has a dilution ratio of about 1:15 with inlet
water pressures of 30 psi. Changes in inlet water
pressures, flow rate or any factor creating back
pressure on the output side of the proportioner, such as
a constrictive nozzle or a kink in the hose, will alter the
Usually, 50 feet or less of hose is used, although some
line pressure drop occurs regardless of hose length.
The Siphon Mixer has a dilution capacity of 1 gallon of
concentrate in 5 minutes, which means about 15 to 16
gallons of diluted fertilizer are delivered in 5 minutes.
The Siphon Mixer generally is used for hand fertiliza-
*Tradenames and companies are mentioned with the
understanding that no discrimination is intended nor en-
tion of small numbers ofplants. Water should be drawn
into the fertilizer inlet after completing fertilization to
wash out salts and avoid corrosion of the ball valve
Displacing concentrated fertilizer solution into ir-
rigation water is another example of pressure differen-
tial injection. One type of displacement injector con-
tains a collapsible rubber bag inside a metal tank. As
water fills the tank, the bag containing the fertilizer
concentrate collapses, forcing fertilizer into the irriga-
tion water. This injector contains few moving parts;
however, inlet water pressure and flow rate may alter
injection accuracy. Flow control valves can be used to
compensate for variations in inlet flow rate. Mixer-
Proportioner and Gewa (Fig. 2) are injectors that
operate with this principle and have variable dilution
ratios and various sizes of injector tanks.
. -. Fig. 2. Mixer-Proportioner (above) and Gewa (right) are pressure
. .-. differential injectors that contain collapsible bags.
Fig. 1. Siphon Mixer is a pressure
differential injector utilizing
the venturi principle.
Fig. 3. Merit Commander (right) and Smith Measuremix (above)
are water-motor positive displacement proportioners.
Anderson Ratio-Feeder (left) Baggaley HPA
(above) and T.M.B. (right) are water meter-
controlled positive displacement proportion-
Water Motor-Controlled Injectors
Water motor-driven proportioning injectors use
water flow to operate a piston or diaphragm to inject or
force fertilizer into the irrigation water by positive
displacement. As water flows through the injector, the
water causes a cam to turn and push a piston back and
forth. Consequently, oscillation of the piston varies.
Examples include the Merit Commander and the
Smith Measuremix (Fig. 3). The Commander is a light
duty, small volume unit which should be reserved for
small areas or spot treatments, while the Measuremix
is available in several models to accommodate several
different flow requirements and dilution ratios.
Water Meter-Controlled Injectors
These injectors use a water meter mechanism to
determine flow rate, and water-powered diaphragm
pumps to inject the fertilizer. The Anderson Ratio-
Feeder, the Baggaley HPA and the T.M.B. injector (Fig.
4) are water meter-controlled positive displacement
proportioners. The Baggaley HPA requires a small
amount of electricity to power solenoid valves that
regulate water flow to and from the diaphragm pump.
Positive Displacement Fertilizer Pumps
This type of equipment displaces a fixed amount of
concentrated fertilizer each time fertilizer is forced
into the irrigation water. A piston (or piston and
diaphragm) is often used to displace the fertilizer. In-
jectors of this type usually are driven electrically and
should have a common electrical circuit with the ir-
rigation water pump so the injector will stop at the
same time as the irrigation pump. Examples of elec-
trically driven positive displacement injectors are
Milton Roy and PULSAfeeder (Fig. 5). Both of these in-
jectors contain a piston that forces oil against a
diaphragm to displace the concentrated fertilizer.
Since several metering pumps operate reliably with
a back pressure of 100 psi or more, obtain advice from
the manufacturer regarding the optimal range of
operating pressures for individual pumps. Most
nursery irrigation systems operate at approximately
40 psi, so it is often desirable to install a preset back
pressure valve between the metering pump and point
where the fertilizer is injected into the water line.
The fertilizer quantity injected is constant regard-
less of water flow, so the system should be checked fre-
quently because inadequate or excessive quantities of
fertilizers could be injected. An option for electrically
driven positive displacement pumps is to attach an ir-
rigation water flow sensor to the injector pump. In this
way, the length of intermittent injection time or speed
of injection can vary with water flow. More precise fer-
tilizer concentrations are achieved with systems
capable of sensing water flow.
A sensor can also be used to measure the conduc-
tivity (soluble salts) of the irrigation water after injec-
tion and relay electric impulses to solenoid valves or in-
jector, thus controlling the intake of concentrated fer-
tilizer by the injector. Sensors that detect irrigation
water conductivity must be calibrated for different fer-
tilizers. A system to monitor conductivity or sense
water flow should also allow manual alteration of the
When positive displacement injectors are used, a
blend-tank may be needed in the water line im-
mediately following the point of injection to ensure
adequate mixing of water and fertilizer. This is
especially true if the fertilizer passes through pipe of
insufficient length for mixing.
Factors to Consider When
Selecting an Injector
Consider these factors when selecting an injector. All
may not be applicable to your situation.
1) Injector must be compatible with the water flow
2) Irrigation line pressure and flow rate must
achieve the desired quantity of water and fertilizer
delivered in the allotted time.
3) A portable injector unit that can handle greater
Fig. 5. Milton Roy (left) and PULSAfeeder (above) are electrically driven
positive displacement injectors.
suction-side of pump
from storage tank
. Check Valve
Fig. 6. Safety equipment for pump suction injection with noncontinuously pressurized system; approved for fertilizer
only with surface water source.
Fig. 7. Safety equipment required with collapsible bag injection.
irrigation water flow rates than currently used should
be selected to accommodate nursery expansion.
4) Repair parts and dependable service should be
5) Employees must be competent to apply the
mathematical formulas for fertilizer dilutions.
6) Injector dilution ratio may be fixed or variable. It
is sometimes desirable to select an injector with
variable dilution ratios if different fertilizer concentra-
tions will be applied.
7) Consult dealer or manufacturer about the
chemicals that can be injected. Some chemicals have
abrasive particles or properties that corrode the injec-
tor, causing excessive wear of internal metal parts or
premature disintegration of diaphragms.
8) Multiple injection units may be desirable for in-
jecting more than one fertilizer or chemical at the same
9) Pressure-differential injectors are usually less ac-
curate than motor or meter styles, which is an impor-
tant consideration when injecting small amounts of
chemicals such as acids.
10) Large volumes of fertilizer can be injected rapidly
with pressure differential injectors since small dilu-
tion ratios are common, whereas water-motor or
water-meter injectors have large dilution ratios.
11) Water-motor injectors will usually decrease line
pressure more than water-meter styles.
12) Pressure-differential injectors are generally less
expensive than motor or meter styles, but the limited
volume of concentrate and small dilution ratios
necessitate replenishing the stock solution often.
13) The size or capacity of an injector should be based
on water flow, not pipe size.
14) Injector operation must be checked frequently to
ensure proper dilution.
Florida law requires that irrigation systems have
antisiphon devices when chemicals are injected into
the irrigation water. These devices prevent backflow
or flow of chemicals into the water source. The person
responsible for injecting chemicals into irrigation
water must ensure that backflow does not occur.
Backflow for most injection systems is prevented by
antisiphon devices and other safety equipment
diagrammed in Agricultural Engineering Fact Sheet
AE-58, and IFAS Extension Bulletin 217. These
publications and variances can be obtained from your
County Extension Office. Specific details, such as
those for vacuum breakers, valves, low pressure drains
and fertilizer storage tanks, are discussed.
An example of safety equipment required when uti-
lizing pressure differential injection, such as the inlet
side of the irrigation pump or collapsible bags, is shown
in Figs. 6 and 7, respectively. Some venturi-type
injectors have manufacturer-installed backflow
preventers. However, make sure manufacturer in-
stalled backflow preventers meet all requirements of
the Florida backflow prevention law. In addition to the
safety devices described here and in other publica-
tions, local ordinances and municipal regulations
specify additional safety equipment that may be re-
quired. Obtain details for safety equipment inspection
that must be conducted regularly.
Manufacturers of Equipment Listed in This Publication
Hyponex Corporation (Siphon Mixer)
3489 Sawmill Rd.
Copley, OH 44321
Young Industries (Mixer-Proportioner)
1033 Wright Ave.
Mt. View, CA 94043
G. Wagner (Gewa)
Apparatebau GMBH & Co. KG
8900 Augsburg 31
Merit Industries, Inc.
P.O. Box 8075
Cranston, RI 02920
Smith Precision Products Co.
1299 Lawrence Dr., P.O. Box 276
Newbury Park, CA 91320
H.E. Anderson Co.
2100 Anderson Dr.
P.O. Box 1006
Muskogee, OK 74401
34 Rothschild St.
PO. Box 1
Kiriat Bialik 27 100
Milton Roy Co.
Flow Control Division
201 Ivyland Rd.
Ivyland, PA 18974
77 Ridgeland Rd.
Rochester, NY 14623
This publication was produced at a cost of $1336.00, or 24.3 cents per copy, to guide commercial nursery and green-
house operators in selecting and using injectors for fertilization. 6-5.5M-87
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, K.R. Tefertiller,
director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and
June 30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institu-
tions that function without regard to race, color, sex or national origin. Single copies of Extension publications (excluding 4-H and Youth publica-
tions) are available free to Florida residents from County Extension Offices. Information on bulk rates or copies for out-of-state purchasers is
available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this publication,
editors should contact this address to determine availability.