Fertilizer Injectors Made Easy
by
Since the introduction of injectors or proportioners growers have
enjoyed an easy, time- and labor-saving application of liquid chemical
solutions to their crops. These devices
are used to apply water-soluble fertilizers, pesticides, plant growth
regulators, wetting agents, and mineral acids.
They are a vital part of the modern greenhouse or nursery
operation. Yet, probably every grower
has a story to tell about a compromised, damaged or even ruined crop where the
cause was traced to a malfunctioning injector.
Just like with any mechanical device, proper and frequent maintenance
and calibration are crucial steps to ensure optimal injector performance.
Injectors work on one of two principles. Venturi-type injectors, such as Hozonâ and Syfonexâ use a pressure difference
between the water line and the stock tank to draw concentrated solutions into a
faucet connection and mix them with water in the hose. These inexpensive injectors can be easily
attached to any faucet but do not allow precise control over chemical
application. Because of water pressure
fluctuations, variable amount of chemical may be injected into the hose. In addition, the proportion
ratios are low (typically 1:15) and therefore require large stock tank, thus
limiting the use of Venturi-type injectors to small growing areas.
Positive displacement injectors, such as
When Choosing an Injector…
The choice of an injector should be made after some important
aspects have been considered.
·
Size of operation, fertility programs and types of
crops grown
·
Water flow rate (see sidebar for calculation of water
flow rate)
·
Stock tank size – should be based on proportion ratio
and daily water usage
·
Chemicals being injected, particularly if acid
injection is desired
·
Multiple injection heads (for incompatible chemicals)
·
Pressure required for proper operation of the injector
·
Portable or stationary injector
·
Ease of repair and longevity of the unit (if the
repair cost is equal to half or more of the cost for a new unit, replacement of
existing injector is advised).
·
Manufacturer’s reliability, technical support,
service, and other qualifications. Many
manufacturers have websites with useful information about their products;
browse through their catalogs on line.
When Installing an Injector…
Consider installation of additional equipment for optimal
performance:
·
A 140 or 200-mesh filter is recommended upstream of
the injector unit.
·
Pressure regulator if in-line water pressure exceeds
the maximum allowable for the unit; a one-way check valve may be helpful
against water hammer.
·
A backflow valve to prevent contamination of
irrigation water supply if negative pressure occurs. These valves are mandatory in most states.
·
Install the injector off the main line in case of
malfunction or maintenance.
·
Some injectors come with optional EC meters in the
water line. This makes it very easy to
determine whether the injector functions properly.
·
A blend tank may be needed to assure good mixing of
the water and fertilizer. Whether you
need a blend tank depends on the type of injector and design of the irrigation
system. The company representative can
help you with this.
When Using an Injector…
Some things you should know:
·
Dilution ratio should be known and adjusted as needed (see
sidebar on calibration methods). If
large deviations (larger than 5%) from the expected setting occur, contact the
manufacturer for possible repair or replacement.
·
Soluble fertilizers should be dissolved completely;
use hot water if necessary but allow the solution to cool before starting the
injector.
·
Dilution ratios higher than 1:200 require highly
concentrated stock solutions; fertilizer may not dissolve completely due to
exceeded maximum solubility.
·
Tracer dye in water-soluble fertilizers should not be
used as an indicator of solution’s strength; different fertilizer lots may have
variable dye contents causing variability in intensity of the fertilizer
solutions.
·
Before mixing up different chemicals in the injector,
product labels and manufacturer should be consulted to determine compatibility
of the products. Potential acidity
and/or corrosiveness of the chemicals should be taken into account, especially
if acid injection is planned.
·
Extreme caution should be exercised with acid
injection; injected acid concentrations should not exceed 5%. Selection of a particular acid depends on the
acid concentration and water temperatures.
With every 2 degrees Fahrenheit, the speed of acid reactivity increases
ten fold. When using acids, always have
baking soda at hand. If you come in
contact with acid, quickly cover the acid with a generous amount of baking soda. This will neutralize the acid and minimize
injuries.
·
Constant agitation is needed when applying wettable
powders because they suspend but do not dissolve in water.
·
Stock tank should be covered to prevent algae and/or
debris buildup, contamination, or evaporation of stock solution.
·
Stock tanks need to be opaque. The chelating agents in the fertilizer break down
if they are exposed to light. Chelating
agents help to make micronutrients available to the plants and are needed to
prevent micronutrient deficiencies.
·
If you’re using a large stock tank, make sure that the
stock solution is mixed well before using it.
Water-soluble fertilizers tend to accumulate in the bottom of stock
tanks, which can results in large differences in fertilizer concentrations.
·
Injector should not be exposed to freezing
temperatures as cracking and/or warping may result.
When Caring for an
Injector…
·
Intake strainer should be suspended 3-4” from the
bottom of the solution tank to avoid pulling up undiluted concentrate); never
let the suction tube filter lie on the bottom of the stock tank.
·
Inject clean water after use.
·
Solution tank should be cleaned regularly (weekly or
biweekly, depending on frequency of use) to prevent dirt and scale buildup.
·
Suction tube filter should be cleaned in filtered
water.
·
Strainer should be inspected regularly for clogs
and/or cracks.
·
Inspect and service O-rings.
·
Petroleum based lubricants (Vaseline, lanoline, WD-40,
motor oil) should not be used on dosage pistons or seals.
___________________________________________________________________________________________________________________________
How To’s
How to Check Water Flow Rate
WATER METER METHOD. If a water meter is installed, flow rate can be
obtained easily. Turn on the irrigation
system fully and read the meter at a specific time. Take a second reading after the water has run
for a period of minutes. Convert the
difference between the beginning and ending meter readings from cubic feet
(which most water meters measure in) into gallons by using the following
formula:
RATE OF FLOW = 7.5 x [ meter
B – meter E] / minutes
where,
RATE
OF FLOW is expressed in gallons per minute,
meter B is beginning meter reading,
meter E is ending meter reading,
minutes is duration of test.
OPEN
CONTAINER METHOD. If the water supply
flows through a single orifice, a suitable container can be used to measure the
water flow rate. Turn on the flow fully,
and time how many minutes it takes for the tank to fill. Divide the capacity of the tank in gallons by
the number of minutes to obtain flow in gallons per minute.
How to Calibrate an Injector
Periodic
calibration is needed to ensure that an injector is operating properly.
DILUTION RATIO. Collect a known amount of
fertilizer solution from the injector then measure the quantity of concentrated
fertilizer that was taken up by the injector.
Determine the dilution ratio by the following formula:
DILUTION
RATIO = DILUTED VOLUME ÷ STOCK VOLUME
where,
DILUTED
VOLUME is the known amount of fertilizer solution after it has passed through
the injector,
STOCK
VOLUME is the amount of concentrated fertilizer solution that was used during
the test.
Start
test by turning the injector on to remove air bubbles and charge the system
with concentrated stock solution. Turn
off the unit, remove the intake or suction tube from stock tank, and place it
in a large volume (minimum 500 ml) graduated cylinder. Fill the cylinder with a known volume of the
concentrated stock solution. Turn on the
injector and collect a known volume of diluted fertilizer solution (e.g. 5
gallons).
EXAMPLE. Injector is set for a 1:50
ratio. If (in the above test) 370 ml of
concentrate was used to make 5 gallons (18,925 ml) of diluted solution, the
actual ratio is 18,925 ÷ 370 = 51. This
is close to expected, because it is off only by 1%. Repeat this test several times.
You
should also check the manual of your injector for other ways to test your
specific injector.
ELECTRICAL CONDUCTIVITY (EC) MEASUREMENT.
This
easy method is commonly used for water-soluble fertilizers. It does not require collection of large
quantity of fertilizer solution and is an excellent means of periodic
monitoring of the fertilizer program.
Critical element for this method is to follow precisely the fertilizer
manufacturer’s guidelines for mixing up concentrated solutions. Fertilizer suppliers generally provide
charts with EC readings of various concentrations of water-soluble fertilizer
solutions. When measuring the required
quantity of fertilizer (usually given as a weight amount), use a scale to
ensure right amount. Using other
measuring means, e.g. coffee cans, plastic cups, etc., will result in erroneous
reading of EC due to variability in the fertilizer quantity used to make up the
concentrated solution. Only reliable,
calibrated conductivity meters should be used to ensure accuracy of
reading. Standardized conductivity
solutions are available from the measuring device manufacturer and should
always be kept at hand.
Start
test by collecting an on site sample of clear irrigation water. Let the water run for a few minutes to flush
out pipes before collecting the sample.
Measure the EC of this water sample and record it. Turn the injector on and run it for a few
minutes before collecting a sample of the fertilizer solution in a clean
container. Test and record EC of the
fertilizer solution. Calculate the EC
contributed by the fertilizer by the following formula.
EC
FERTILIZER = EC FERTILIZER SOLUTION – EC IRRIGATION
WATER
Compare
this reading to a chart from the manufacturer bag label.
EXAMPLE. Injector is set for a 1:50
ratio. 10.1 oz of 20-10-20 fertilizer
for each gallon of stock mix is used at a concentration of 300 ppm N. If (in the above test), the EC IRRIGATION
WATER is 0.3 mmhos/cm and the EC FERTILIZER SOLUTION is 2.10
mmhos/cm, the actual EC FERTILIZER is 2.10 – 0.3 = 1.8
mmhos/cm. The technical chart for this
particular fertilizer lists that the expected EC for 300 ppm N is 1.86 mmhos/cm.
Therefore the actual dilution ratio is off by a factor of about 3% (1.86
÷ 1.8 = 1.033). This method gives a
ballpark estimate on the fertilizer program.
Regular testing of the fertilizer EC is an effective means of monitoring
injector performance. Make sure to
calibrate your EC meter before using it!
Without calibration you will get poor results and make the wrong
decisions concerning your fertilizer program.
SOME
HELPFUL FORMULAE AND CONVERSIONS
To convert from injection ratio to percent: To convert from percent
to injection ratio:
(100 ÷ injection ratio) 100 ÷ percent = injection ratio
EXAMPLE (100 ÷ 50) = 2% EXAMPLE: 100 ÷ 2% = 1:50
METRIC CONVERSIONS
|
TO CONVERT FROM |
TO |
MULTIPLY BY |
|
Gallons Grams Liters Ounces
(weight) Ounces
(fluid) Pints
(fluid) Pounds Quarts
(fluid) |
milliliters cubic feet liters ounces fluid ounces quarts gallons grams, milliliters liters milliliters liters grams cubic in. milliliters liters |
3785 0.134 3.78 0.03527 33.8 1.06 0.264 28.35 29.6 0.0296 473 0.473 454 67.2 0.946 |
Bodie V. Pennisi is extension floriculture specialist,
University of Georgia, Department of Horticulture,