D. S. HARRISON
Injection of Liquid
UNIVERSITY OF FLORIDA
AGRICULTURAL EXTENSION SERVICE
Cover photograph shows a precision commercial in-
jector unit for installation in irrigation mainline.
The author, D. S. Harrison, is Associate Agricultural Engineer
with the Florida Agricultural Extension Service, University of
Injection of Liquid Fertilizer
Materials Into Irrigation Systems
Dalton S. Harrison
Associate Agricultural Engineer
Fertilizer materials were first applied through irrigation
water in California about 1930. Since then it has been practiced
with varying degrees of success in many areas of the United
States, including Florida.
There are many advantages in using an irrigation system
to apply fertilizer. A major advantage is that labor required
for both irrigation and fertilizer is only slightly greater than
that required for irrigation alone. In addition to good surface
distribution, excellent control can usually be maintained on place-
ment depth of some fertilizer materials, especially nitrogen.
As another advantage, nutrients become available to plants
sooner than when applied on the ground, since they are already
in solution. And, less fertilizer may be required throughout the
But, there are certain disadvantages to fertilizer application
through irrigation systems. An improperly designed system will
not give equal distribution. Lower cost fertilizer materials often
cannot be used. Localized fertilizer placement cannot be obtained
as in conventional band placed applications. Materials contain-
taining phosphoric acid concentrate near the surface of the soil
and anhydrous ammonia and free ammonia in other nitrogen
solutions may be lost into the air when applied through irriga-
tion water. Free ammonia also may damage the green foliage.
Persons trained in soils and use of fertilizers should be con-
sulted before promiscuously using any material in an irrigation
Methods of Injection
Centrifugal Pump: This is perhaps the easiest method of
injection. The procedure is to connect one line from the open
fertilizer tank to the suction line of the pump, thus letting the
pump draw the fertilizer into the intake side. A valve is needed
in this line to adjust intake rate and to cut off fertilizer when
irrigating only. On the discharge line of the pump a line should
be installed for filling the fertilizer tank. A barrel or open
container made of concrete block will suffice as a container for
the fertilizer solution.
This method, also referred to as the "two-valve" method,
is illustrated in Figure 1.
1 To Water Supply
Fig. 1.-Equipment and arrangement necessary
for a centrifugal pump.
Deep-well pumps (Method No. 1): Since deep well pumps
do not exert suction in any part of the systems above the
ground, the fertilizer solution must be introduced either into
the well or the discharge line. A common method, especially
adapted where electric power is available, is to use a small
rotary, gear or piston pump to inject the solution into the
discharge line (Figure 2). The fertilizer injector pump must be
able to deliver a higher pressure than that coming from the
Deep Well Turbine
Fig. 2.-Equipment and arrangement necessary for injection
into the discharge line of a deep-well turbine pump, using
a motor driven fertilizer pump.
main irrigation pumping plant, but at relatively low rates. It
may be driven by electric or air-cooled motor.
One of the most popular methods, where an auxiliary motor
is not desired, is to mount a jack-shaft to the main irrigation
power unit. The fertilizer injection pump is then driven by
the power-take-off shaft and a separate clutch is installed.
Several of these units are now operating in the state. The
advantage of such an arrangement is elimination of an auxiliary
power unit for the fertilizer injection pump.
Gear pumps, especially those with bronze gears, may be
severely damaged by the fertilizer solution.
One such system is now in use by Nelson Brothers Nursery
near Apopka, where 12 acres of roses are fertilized through
this type irrigation system.
Deep-well pumps (Method No. 2): An aspirator unit is used in
another method of injection. With this method, a portion of the
water discharged from the irrigation pump is by-passed through
the aspirator (an apparatus for producing a movement of fluids
by suction), creating a suction that draws the fertilizer solution
into the line. Figure 3 shows details and arrangement of this
method. An open fertilizer tank can be used.
-Deep Well Turbine Pump
Tube to Aspirator
Fig. 3.-Arrangement of equipment necessary
when using an Aspirator unit.
Commercial Units Available: At least three companies man-
ufacture injection units which introduce fertilizer directly into
the irrigation discharge line. These units, complete with tank,
utilize a pressure difference in the line usually between coup-
lers, around elbows, at a reducer, or a special venturi to force
the fertilizer solution into the mainline discharge pipe.
A pressure tank contains the fertilizer solution. The tank
is attached or connected to the irrigation main by two pressure
hoses and valves which are connected to fittings on the mainline
discharge pipe. Costs of these applicators vary from $100.00 to
$600.00. Liquid fertilizer tank capacities vary from 12 to 100
gallons, while dry material capacities vary from 100 to 800
pounds. One model now commercially available (Figure 4) has
a tank capacity of 500 pounds of dry material or 60 gallons
of liquid fertilizer.
Fig. 4.-A commercial injector which utilizes a pressure
differential for feeding solution into sprinkler mainline.
The three companies known to manufacture the above units
are Doerr Metal Products, Lamed, Kansas; Dragon Engineering
Co., Oakland 21, California; and Glen Piland Co., Bakersfield,
Another commercial-type injector is a precision unit which
will proportion the liquid material into the line so that the rate
will not vary more than 5 percent regardless of changes in
water flow rate or pressure. The unit consists of two water
motor, direct-driven injector pumps. All the water used is
passed through the water motor. The water motor meters the
water. The positive action piston injector pumps handle the
liquid fertilizer. These units handle water at rates from 25 to
700 gallons per minute with a proportion range of from 1:2000
to 1:800. Price range is from $300.00 to $2200.00. Picture on
the cover of this publication is of this type of injector.
The only company known to manufacture this type of in-
jector is Smith Precision Products Co., South Pasadena, Cali-
Operation and Maintenance
When the equipment is properly flushed out after each opera-
tion, there has been little evidence that the solutions are harmful
to either the pump, pipe or sprinklers; however, phosphoric acid
and super phosphate will cause excessive corrosion and extreme
caution.must be taken. Plastic (PVC) pipe and sprinklers offer
the best solution for corrosion problems.
In general it will take from 30 minutes to 5 hours to inject
the fertilizer solution. After ferti-gation, depending on the
concentration of fertilizer used, allow additional running time
to flush fertilizer from the system and to wash all the fertilizer
off the plants.
If irrigation is to be done at the same time as fertilization,
the ferti-gation should be done toward the end of the application
period or setting.
Fig. 5.- Arrangement of a commercially available aspirator
for applying fertilizer solutions to lawns.
Injection Into Lawn Irrigation Systems
This discussion thus far has been primarily for field irriga-
tion systems and would have little application to home lawn
Where the home-owner desires to inject fertilizer into an
irrigation line utilizing only one sprinkler, a commercially avail-
able aspirator, as shown in Figure 5, should be used. Another
type of aspirator, now available commercially, is the "quart jar"
model which attaches directly to the garden hose. Remember
that aspirators will reduce water pressure; therefore, be sure
to have one which will allow the sprinkler to operate properly.
When injecting fertilizer into all or part of a lawn irrigation
system, a commercial model injector, as previously discussed
under commercial units, should be used. A 12-gallon tank unit
should be sufficient.
To find the amount of fertilizer to apply, measure the radius
of the area covered by a full circle sprinkler; then refer to
Table I. To determine the amount of fertilizer needed for this
area, refer to Table II. This table lists some of the fertilizer
materials which might be needed or used on lawn grasses. Con-
sult your local county agricultural agent for recommendations.
Inject the fertilizer through the sprinkler system. Allow
water to run an extra 10 minutes to flush the system and wash
the fertilizer off the grass. Fertilizer solutions can be drawn
into the sprinkler system with an aspirator. This device usually
is attached to the water faucet and then the hose attached to
Extreme caution should be taken when injecting anhydrous
ammonia, aqua ammonia, phosphoric acid, or super phosphate
through a sprinkler system. The ammonia fertilizer will evapo-
rate into the air, while the others may cause excessive corrosion.
TABLE I. AREA COVERED BY SPRINKLER
(measure from center to edge)
Radius covered by Area in
sprinkler in feet sq. ft.
Length & Width Area in
covered in ft. sq. ft.
20' x 10'
30' x 15'
40' x 20'
50' x 25'
60' x 30'
70' x 35'
TABLE II. FERTILIZERS & APPLICATION RATES
(To Apply Nitrogen at Rate of 1 lb. per 1000 Sq. Ft.)
Area Covered by Sprinkler in Sq. Ft.
Analysis 100 500 1000 1500 2000
Amount of Fertilizer to Apply
45-0-0 14 lb. 1 lb. 214 lbs. 31/ lbs. 4/2 lbs.
33.5-0-0 1/4 lb. 11/ lbs. 3 lbs. 4%/ lbs. 6 lbs.
20-0-0 12 lb. 212 lbs. 5 lbs. 7/2 lbs. 10 lbs.
13-39-0 % lb. 3% lbs. 7% lbs. 11/2 lbs. 151/2 lbs.
16-20-0 % lb. 3 lbs. 614 lbs. 9% lbs. 12/2 lbs.
11-18-0 1 lb. 41/2 lbs. 9
10-6-4 1 lb. 5 lbs. 10
lbs. 13% lbs. 18% lbs.
lbs. 15 lbs. 20 lbs.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director