The Cross Section, Volume 33, Number 1, January 1987 Page: 2
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Page 2 THE CROSS SECTION January 1987
Safety Precautions Prevent Aquifer Contamination
Chemigation Systems Gaining Po
polarity
Today, many producers are using
their irrigation systems to apply
agricultural chemicals to their fields
through a process commonly known
as chemigation. The process involves
injecting an agricultural chemical
into an irrigation pipeline so that the
chemical mixes with the irrigation
water. The water/chemical solution
is then distributed over the field
through the irrigation system.
Chemigation is an effective and
economical method of applying
agricultural chemicals such as
pesticides, fertilizers, herbicides and
fungicides. Chemigation can be used
in both soil treatments and plant
applications with any irrigation
system, although continuously
moving lateral sprinkler irrigation
systems and center pivots are the
most common. A chemigation
system is normally composed of an
irrigation pump, a chemigation
pump, a chemical tank and a back-
flow prevention system to prevent
contamination of the water supply.
According to E. Dale Threadgill,
Professor and Head of the Agricul-
tural Engineering Department at the
University of Georgia, chemigation
use has increased rapidly over the
last few years, with an estimated
12.8 million acres chemigated in the
United States in 1985.
Chemigation Advantages
Chemigation offers several
advantages. It can provide excellent
uniformity of application, because
the application efficiency of sprinkler
systems is considerably higher than
the application efficiency of air-
planes. Also, chemicals distrib-
uted through a chemigation systemcan be applied whenever the plant
needs them, because application is
not dependent upon the weather or
upon the availability of a pilot, as
with aerial application. Further,
compounds which require water for
incorporation are applied with waterand thus are activated immediately.
Use of chemigation also reduces soil
compaction and mechanical damage
to crops, because it reduces the
number of tractor trips through the
field.
Economics
Chemigation may also be economi-
cally advantageous. Dr. Bill Lyle,
Professor and Irrigation Researcher
with the Texas Agricultural Experi-
ment Station in Lubbock, is working
with a Multifunction Irrigation
System (MFIS) to study irrigation and
chemigation. "Through use of our
MFIS system and the in-canopy
application that we are able to get
through this system, we have found
that we can drastically cut the
amount of chemical that is used. We
are getting results in greenbug
control on grain sorghum with 1/16
of the recommended rates," states
Lyle. "With chemigation, in specific
management cases, it may be
possible to reduce the amount of
chemical applied and still get good
results."
According to a 1985 analysis by
Threadgill, multiple chemigation
applications within one year are very
cost effective. However, a single
chemigation application in a year is
probably cost effective only for those
chemicals which require water for
incorporation.
Costs for chemigation range from
34 to 60 percent of conventional
chemical application costs, according
to Threadgill. The costs generally
decrease as the number of chemiga-
tions increase. As a general rule,
chemigation will normally cost no
more than aerial or tractor applica-tions, and in most cases, will cost
one-third to one-half of the cost of
applying chemicals by airplane or
tractor, Threadgill reports.
Chemigation Safety
While chemigation can be aneconomical farm management tool,
proper care should be taken with its
use. Chemigation must be managed
correctly to maintain human and
animal safety and prevent contam-
ination of the environment by toxic
chemicals.
Ground-water contamination is
one of the most obvious dangers
associated with chemigation. The
potential for accidental contamina-
tion of the ground-water supply
could occur if the water/chemical
mixture were to backflow into the
well. An unexpected shut down of
the irrigation pump due to electrical
or mechanical failure, combined with
continued operation of the chemical
injection system after the irrigation
pump has shut down, could allow
the water/chemical mixture to flow
back into the well, thus contam-
inating the aquifer.
The risks of ground-water contam-
ination can be substantially reduced
with the use of a backflow preven-
tion system. Some states, like Kansas
and Georgia, require a backflow
prevention system by law. "There
are commercially available packages
that give you all the required
equipment," says Lyle.
"Use check valves on your irriga-
tion pipeline that prevent movement
of water back into the well when the
well stops pumping. The check valve
automatically closes if the irrigation
pump shuts off. Thus water cannot
flow back through the line into the
well. Along with the check valve
there is a required suction breaker,
which is actually an air vent, that
opens preventing a vacuum from
being created by falling water when
the pump shuts off. This preventschemicals from being sucked past
the closed safety valve," Lyle
explains. Both the check valve and
vacuum relief valve should be
located on the irrigation pipeline
between the irrigation pump and the
injection line.Lyle notes that if a chemical did
backflow into the ground water, the
chemical will either be absorbed into
a clay soil particle or stay in the
water solution.
"If a chemical backflows into a
well, the likelihood of it moving from
that location is fairly remote. Water
that drains back into the well will not
move very far in a short period of
time, meaning a few hours to a few
days. Hopefully, the chemical solu-
tion can be pumped back out soon.
If absorbed on a clay soil particle in
the aquifer, it won't move either, but
will remain tied up at that location."
A chemical in solution will stay in
the vicinity of the well because for a
short time after pumping stops,
ground-water flow caused by
pumping runs toward the well, even
as water levels immediately around
the well begin to recover. This tends
to trap any back-siphoned chemicals
within the well or in the immediate
vicinity of the well. Thus, if pumping
restarts soon after the shutdown, the
chemicals can be pumped out of the
aquifer, minimizing the potential for
ground-water contamination.
"We don't want the chemicals
down in the aquifer, but if the well
can be restarted fairly soon, 99
percent of the chemical can be
retrieved out of the well," says Lyle.
An automatic low pressure drain
further insures that chemicals will
not flow back into the water supply
should the irrigation pump shut off.
Placed on the bottom side of the
irrigation pipeline between the check
valve and the irrigation pump and
always before the point of chemical
injection, the drain catches any
chemical mixture that might leakChemigation Safety Devices And Arrangement
Engine Drive
vacuum irrigation
a e oatmen
relief valve pipe line - irr~Aln
& inspection
automaticS
low pressure
check drain
valve 0SCeARGE 20or
belt driven
chemical -
discharge line s ucion line
chemical
tank
sudtion line
strainerMotor Drive
irrigation electric motor
reifvalvem pipe line and Pupsn
& inspection
electrically interloiked
control panels
achermacac
stlow essurel
aaine
check DISCHARGE 20 FT
valvee ,RMWL
electric motor
chemical conduit
discharge line PUPsuction line
chemicals
suction hine
strainerThese two arrangements of a chemigation system, engine driven (left) and motor driven (right), include the minimum safety equil
and show the positioning of the equipment in a backflow prevention system. The diagrams were designed by P.E. Fischbach, D.E. Eisen
and D.R. Hay and are reprinted courtesy of the University of Nebraska-Lincoln, Agricultural Engineering Department, Cooperative Exte
Service and Institute of Agriculture and Natural Resources.pment
hauer
1nsionthrough the check valve and
channels it away from the water
supply.
Lyle explains, "The minute the
pump stops and removes the positive
pressure of the water, the water that
trickles by runs out the drain."
Another check valve may be
installed on the chemical injection
line to stop the flow of water from
the irrigation system into the
chemical supply tank and to prevent
gravity flow from the chemical
supply tank into the irrigation
pipeline after an unexpected
shutdown. If the injection pump
stopped unexpectedly and irrigation
water flowed into the chemical
supply tank, the tank could overflow,
causing a spill around the irrigation
well.
"You also need a device that will
stop the injection pump when the
irrigation pump stops. If the
irrigation pump stops, you don't
want chemicals running into the
main system," Lyle says.One way to make sure both pumps
shut down is to interlock thePage 2
T HE C ROS S S EC T IO N
January 1987
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Reference the current page of this Periodical.
High Plains Underground Water Conservation District No. 1 (Tex.). The Cross Section, Volume 33, Number 1, January 1987, periodical, January 1987; Lubbock, Texas. (https://texashistory.unt.edu/ark:/67531/metapth1533142/m1/2/: accessed July 11, 2024), University of North Texas Libraries, The Portal to Texas History, https://texashistory.unt.edu.; crediting UNT Libraries Government Documents Department.