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Title: Injection of fertilizers into drip irrigation systems for vegetables
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Title: Injection of fertilizers into drip irrigation systems for vegetables
Series Title: Injection of fertilizers into drip irrigation systems for vegetables
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Creator: Kovach, Steven P.
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Full Text

October 1984


Injection of Fertilizers Into Drip
Irrigation Systems for Vegetables

S. P. Kovach


(cLc


K,! : 1 3 io,:1


-y I
Florida Cooperative Extension Service / Institute of Food and
Agricultural Sciences / University of Florida / J. T. Woeste, Dean


Circular 606









Injection of Fertilizers Into Drip

Irrigation Systems for Vegetables

S. P. Kovach*


Introduction

In recent years, commercial vegetable growers in
Florida have shown an increased interest in drip
(trickle) irrigation as a means of irrigating crops.
Drip irrigation is the use of plastic irrigation lines
and their emitting orifices to supply water at a low
rate to the crop's root zone. Drip irrigation is used
not only to supply water but also can be used to sup-
ply soluble materials such as fertilizers, fumigants,
insecticides, fungicides, or herbicides. This method
is called "chemigation".
The process of adding soluble fertilizer by means
of the drip system is called "fertigation". The ad-
vantages of applying fertilizers through the drip
system are: (1) labor savings; (2) energy savings; (3)
improved fertilizer use efficiency; and (4) greater
flexibility in timing of fertilizer applications. With
the option of injecting fertilizers into the drip irriga-
tion system, fertilization can take place at any time,
regardless of a crop's growth stage or the field's ac-
cessibility to machinery.
Fertilizers injected into the drip irrigation system
tend to be more efficiently utilized than dry fertil-
izers applied in bands or broadcast prior to planting.
The increased efficiency is due to a smaller amount
of fertilizer maintained in the soil at any particular
time and, therefore, loss from leaching and run-off
during heavy rainfall may be minimal over the en-
tire crop season. Fertilizers injected into the drip ir-
rigation system in proper amounts provide less
danger of injuring the plant's root system, since the
liquid fertilizer is greatly diluted in the irrigation
water.


Fertilizer Elements That Can Be
Applied Through Drip Irrigation
Systems
Nitrogen

Nitrogen (N) is the element most frequently in-
jected into drip irrigation systems, as it is readily
leached from sandy soils and must be replenished to


maintain good crop growth. N is generally injected
into the system as ammonium nitrate, potassium
nitrate, or as calcium nitrate when bicarbonates are
low. Anhydrous ammonia, aqua ammonia, and am-
monium phosphate should not be injected into drip
irrigation systems due to the clogging hazard they
present to the system. The pH of the irrigation
water should be known at the time of fertilizer injec-
tion since some nitrogen sources will increase the
pH of the water. By increasing the pH of the water,
the threat exists that insoluble calcium and mag-
nesium carbonates present in some water sources
may precipitate and clog emitting orifices.

Phosphorus

Injection of phosphorus (P) into drip irrigation
systems is generally not recommended for the fol-
lowing reasons: (1) properly applied preplant P
satisfies the plant's P needs; (2) P is limited in its
movement in the soil; and (3) the P injected into the
drip system may present a clogging hazard to emit-
ting orifices because of other minerals in the irriga-
tion water.

Potassium

Potassium (K) is also easily leached in sandy soils
and generally must be replenished to maintain a
proper N:K ratio for good crop production and
quality. K can be injected into the drip irrigation
system as potassium sulfate, potassium chloride, or
potassium nitrate.

Micronutrients

Generally, micronutrients can be applied preplant
for most crops and in most soils, and is the recom-
mended way to supply micronutrients to drip irri-
gated crops. If applied via the drip system,
micronutrients such as iron, zinc, copper, and
manganese can be injected as chelates or sulfates.
Sulfate salts of micronutrients may react with salts
in the irrigation water and cause precipitation and


*Former Assistant Professor-Extension Water Specialist, Vegetable Crops Department, Institute of Food and Agricultural Sciences,
University of Florida, Gainesville, FL 32611









clogging. Chelated micronutrients are highly water
soluble and usually cause little clogging or pre-
cipitation.




Injection Methods

The following are principal methods used to inject
fertilizers into drip irrigation systems: (1) pressure
differential; (2) the Venturi (vacuum); and (3) meter-
ing pumps (Figure 1). It is essential that drip irriga-
tion systems equipped with a chemical injection
system have a vacuum breaker (anti-siphon device)
and a backflow preventer (check valve) installed
upstream from the injection point. The vacuum
breaking valve and backflow preventer will prevent
chemical contamination of the water source in case
of a water pressure loss or power failure.



General Fertilization Procedures

1. Approximately 30-40% of the N and K, and
100% of the P, secondary elements (Ca, Mg, and S)
and micronutrients should be applied to the plant
bed as a broadcast application and incorporated into
the plant bed. Although fertilizer placement in drip-
irrigated beds has not been determined for each of
the commercial vegetable producing areas in Florida,
incorporation of fertilizers into the plant bed has
been shown to be better than banding on the soil
surface. If fertilizer is banded in the plant bed, the
fertilizer band must be within the wetting pattern of
the soil. The remaining 60-70% of the N and K
should be injected into the drip system during the
growing season.
2. Fertilizers may be injected into the drip irriga-
tion system daily, two times/week, or one time/week.
3. The rate of fertilization for the total growing
season for a given crop is the recommended fertiliza-
tion rate for the crop grown with conventional ir-
rigation systems. The quantity of fertilizer to inject
will depend on the stage and rate of growth of the
crop. In a research study on drip irrigation of to-
matoes, (Locascio 1982), N and K (60% of the total
season requirement) respectively, were injected
weekly with the following percentages of the total
injected N and K being injected each week (14-week
crop): 0, 2, 4, 6, 8, 12.5, 12.5, 12.5, 12.5, 7.5, 7.5, 7.5,
7.5, and 0%.


4. The drip irrigation system should be allowed to
reach its working pressure prior to the injection of
the fertilizer solution. The length of time (minutes,
hours) that fertilizer is injected into the irrigation
water of a drip system is governed by the length of
time that it takes the fertilizer to reach the farthest
emitting orifice. In order for the injected fertilizer to
be equally distributed among the plants in any sin-
gle irrigation group, only irrigation water must be
run through the drip system after fertilization injec-
tion stops for the same amount of time that it takes
for the fertilizer to reach the farthest emitting ori-
fice. For example, if it takes 5 minutes for the irriga-
tion system to reach its operating pressure, and if it
takes 45 minutes for the injected fertilizer to reach
the farthest emitting orifice, what is the total length
of time for the fertilization cycle? The fertilization
cycle in minutes is equal to 95 minutes (5 minutes
for the system to reach its working pressure + 45
minutes for injection of the fertilizer + 45 minutes
of post-injection irrigation). The amount of time
that it takes the injected fertilizer solution or any
chemical injected into the drip irrigation system to
reach the farthest emitting orifice can be determin-
ed by injecting liquid chlorine (household bleach),
aniline dye or food coloring, or liquid detergent into
the drip system. When liquid chlorine is used as the
indicator method, the water from the farthest emit-
ting orifice should be tested for total chlorine using
a DPD portable chlorine test kit. The reagent used
to measure for total chlorine will turn the irrigation
water pink indicating that the liquid chlorine has
reached the farthest emitting orifice.
5. Fertilizers should not be injected at the same
time that pesticides or chlorine are being injected.
Chlorine is injected into the drip irrigation system
as liquid sodium hypochlorite (NaOCI) to prevent
the formation of bacterial slimes which can clog
emitting orifices of drip irrigation systems. Chlorine
should be injected sometime after the injection of
fertilizers with the injection interval being long
enough to permit 30 minutes of chlorine to reach the
last emitter. For example, if it takes 36 minutes for
the chlorine to reach the last emitter, then the total
time for chlorination will be a minimum of 66
minutes (36 minutes + 30 minutes). The frequency of
chlorination and quantity of chlorine to inject
depends on various water quality factors (pH, and
concentrations of iron and hydrogen sulfide). For
further information on the frequency of chlorination
and quantity of chlorine to inject, contact the local
office of the Florida Cooperative Extension Service
or the University of Florida's Institute of Food and
Agricultural Sciences (IFAS).












Figure 1. Methods for injection of fertilizers into drip irrigation systems.

Venturi Method


Sb
Vacuum breaker Check valve


- Vacuum breaker

valve


Venturi


Tank with
fertilizer
solution


Injection Pump Method


Vacuum breaker Check valve


Check valve

- Vacuum breaker



- Gate valve


<) Injection
pump


Pressure Differential Method


Gate valve

Pressure tank -


Gate valve
Vacuum breaker

Check valve


t I T 1'
Check valve High Press. Press. Low pressure
side reducing side
device


Tank with -
fertilizer
solution


Vacuum breaker
Vacuum breaker










Example


The following example is intended to show how a
fertilization scheduling program may be developed
for a vegetable crop utilizing the practices recom-
mended in items 1 through 5:

Crop: Tomato
Location: SW Florida
Soil Texture: Sandy Soil
Frequency of Fertilizer Injection: Daily
Number of Harvests: 3-4
Length of Growing Season (Weeks): 14
Acres/Irrigation Group: 25

Rate of Fertilization: The recommended fertilization
rate for a tomato crop grown in SW Florida on a
sandy soil on plastic mulched beds is presented in
Table 1.

PREPLANT FERTILIZATION PROGRAM: The pre-
plant fertilization program for the tomato crop is
presented in Table 2.

POSTPLANT FERTILIZATION PROGRAM: The post
plant fertilization program for the tomato crop is


Table 1. Recommended fertilization rate for a tomato
crop grown in SW Florida on a sandy soil on
plastic mulched beds


Fertilizer Element
N
P205
K20C


Fertilization Rate
(Lbs./Acre)ab
Number of Harvests
1-2 3-4
180-220 240-275
50-100 50-100
270-330d 360-413d
360-440e 480-550e
1.5-2.0 1.5-2.0
1.5-2.0 1.5-2.0
3.0-5.0 3.0-5.0
0.5-1.0 0.5-1.0
0.5-1.0 0.5-1.0
0.01-0.02 0.01-0.02


aThe recommended rates are based on the rates recommended
for seepage irrigation (P. H. Everett, Veg. Crops Ext. Rpt.
VEC 83-3).
bRates are based on 7,200 linear bed feet/acre.
CTomato varieties that are susceptible to graywall, yellow
shoulder, andlor blotchy ripening should use K20 rates that
are 1.5-2.0 times the amount of N.
dN:K ratio of 1:1.5
eN:K ratio of 1:2


presented in Table 3. The rates of N and K20 to be
applied are 60% of the total N (275 Ibs./acre) and
KO0 (550 lbs./acre) fertilizer rates.

If a 6-0-12 liquid fertilizer is utilized for the
N + K20 source, how many gallons of liquid fertilizer
will be needed to inject daily into the drip system
during week number 2 of the crop cycle, to fertilize
an irrigation group consisting of 25 acres?
The following information is needed:
1. Rate of N and K20 to apply (lbs./acre):
N = 0.47 (Table 3)
K20 = 0.94 (Table 3)
2. Area to be fertilized (acres): 25
3. Pounds of N and K20/area to be fertilized:
N = 0.47 x 25 = 11.75 lbs./25 acres
K20 = 0.94 x 25 = 23.50 lbs./25 acres
4. Pounds of N and K20/gallon of liquid (6-0-12)
fertilizer:
Weight of 6-0-12 used for calculations is 10
lbs./gal. Actual weight varies depending on nu-
trient sources and formulation.
N = 0.6 lbs./gallon
K20 = 1.2 lbs./gallon
5. Gallons of liquid fertilizer (6-0-12)/area to be fer-
tilized (25 acres):
11.75 Ibs. N/25 acres
1.7 lbs. N/2 19.58 gallons (6-0-12)/25 acres
0.6 lbs./gallon


6. Fertilization cycle:
Preinjection irrigation:
(Length of time that it takes the
drip irrigation system to reach its
working pressure)
Fertilizer injection interval:
(Length of time that it takes the


5 minutes



45 minutes


Table 2. Preplant fertilization program for a tomato crop
utilizing the high recommended fertilizer rate
for 3 to 4 harvests from Table 1.

Fertilizer Percent of Total Fertilizer Fertilization Rate
Element to Be Applied (LbsJAcre)
N 40 110.00
P205 100 100.00
K20 40 220.00a
Mn 100 2.00
Zn 100 2.00
Fe 100 5.00
Cu 100 1.00
B 100 1.00
Mo 100 0.02
aN:K ratio of 1:2










Table 3. Postplant fertilization program for a tomato crop utilizing the high recommended fertilizer rate for 3 to 4 har-
vests from Table 1


% of Fertilizer
to Apply/
Week
0.0
2.0
4.0
6.0
8.0
12.5
12.5
12.5
12.5
7.5
7.5
7.5
7.5
0.0


Lbs. NI
Week/
Acre
0.00
3.30
6.60
9.90
13.20
20.60
20.60
20.60
20.60
12.38
12.38
12.38
12.38
0.00
165.00


Lbs. K20/
Week/
Acre
0.00
6.60
13.20
19.80
26.40
41.25
41.25
41.25
41.25
24.75
24.75
24.75
24.75
0.00
330.00


Lbs. NI
Dayl
Acre
0.00
0.47
0.94
1.41
1.89
2.95
2.95
2.95
2.95
1.77
1.77
1.77
1.77
0.00


Lbs. K201
Dayl
Acre
0.00
0.94
1.89
2.83
3.77
5.89
5.89
5.89
5.89
3.54
3.54
3.54
3.54
0.00


injected fertilizer solution to
reach the farthest emitting
orifice)
Postinjection irrigation: 45 minutes
(Equal to the length of time for
the fertilizer injection interval)

Total 95 Minutes
7. Injection rate (gpm) of the injection pump:
1.5 gpm
8. Gallons of fertilizer solution (water + liquid fer-
tilizer) to inject:
Fertilizer injection Injection rate (gpm)
interval (minutes) of the injection pump

=45 minutes x 1.5 gpm = 67.5 gallons of fer-
tilizer solution.
9. Gallons of water to mix the liquid fertilizer (6-0-12)
into:
Gallons of fertilizer Gallons of liquid fertilizer/
solution (water + area to be fertilized
liquid fertilizer) (25 acres)
=67.5 gallons -19.6 gallons =47.9 gallons of water

Drip irrigation and its accompanying advantages
are examples of technological change occurring in
water and fertility management. The challenge exists
to adapt and maximize drip irrigation according to
Florida's growing conditions. For more information,
consult your county extension agent.


References


1. Bucks, D. A., F. S. Nakayama, A. W. Warrick. Princi-
ples, practices, and potentialities of trickle (drip) irriga-
tion. Advances in Irrigation, Vol. 1:219-298.
2. Elfving, D. C. 1982. Crop response to trickle irrigation.
Horticultural Reviews. 4:1-48
3. Goldberg, D., B. Gornat, and D. Rimon. 1976. Drip ir-
rigation. Drip Irrigation Scientific Publications, Kfar
Shmaryahu, Israel.
4. Howell, T. A., D. S. Stevenson, F. K. Aljibury, H. M.
Gitlin, I Pai Wu, A. W. Warrick, and P. A. C. Raats.
1980. Design and operation of trickle (drip) systems. pp.
663-717. In: Design and Operation of Trickle (Drip)
Systems, M. E. Jensen (Ed.), ASAE Monog. 3, Am Soc.
of Agric. Eng., St. Joseph, MI.
5. Keller, J. and D. Karmeli. 1975. Trickle irrigation de-
sign. 1st ed. Rain Bird Sprinkler Mfg. Corp., Glendora,
CA.
6. Locascio, S. J., J. M. Myers, and J. G. A. Fiskell. 1982.
Nitrogen application timing and source for drip irri-
gated tomatoes. pp. 323-328. In: Proc. Ninth Inter.
Plant Nutrition Colloquium, A. Scaife (Ed.), Warwick
Univ., England.
7. Pair, C. H., W. W. Hinz, C. Reid, and K. R. Frost. 1975.
Drip irrigation. pp. 508-520. In: Sprinkler Irrigation.
The Irrigation Association, Silver Spring, Maryland.
8. Smajstrla, A. G., D. S. Harrison, J. C. Good, and W. J.
Becker. Chemigation safety. Agric. Eng. Fact Sheet
AE-28, IFAS, Univ. of Florida.


Week
Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Total
(Lbs./Acre)














































































This public document was promulgated at a cost of $1160.90, or 35.2 cents per copy, to provide information about
injection of fertilizers into drip irrigation systems for vegetables. 11-3.3M-84


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