8 pp., 6 illustrations, 12 color photosThis publication describes the components of a subsurface drip irrigation system and the procedure for installing such a system. Each step is outlined and illustrated. Steps include tape injection, trenching, connecting drip lines, back-filling, and installing filtration equipment

Enciso, Juan

Texas A&amp;M Repository

The success of a subsurface drip irrigation (SDI)system for row crops depends on its design, instal-lation, operation, management and maintenance.All phases are equally important. This publicationdescribes the components and installation of anSDI system. Steps in the installation process are:• tape injection;• trenching;• installing the mainlines, manifolds (sub-mains) and flush lines;• connecting the tape with the manifolds andflush lines;• back filling; and• installing filtration equipment. Components of theirrigation systemThe main components of an irrigation systemare the filters, mainlines, manifolds (submains),field blocks, flush lines, drip lines (laterals) andaccessories (Fig. 1).  All the drip lines (laterals) connected to thesame submain make up a field block. Several fieldblocks can be grouped together as one station andoperated simultaneously. Water is supplied to driplines in the field blocks by the manifold (submain).In some permanent systems, the drip lines are alsoconnected to a flush line so that accumulated sed-iments can be flushed from the drip lines using asingle valve. The flush line is also called a collectorline. In some field blocks, particularly those withlonger lateral lengths (more than 200 m), the flushline may also be connected to the mainline by aseparate valve and manifold, so that water can besupplied to both ends of the drip line. This pre-vents excessive pressure loss in longer drip lines.The flush line should always contain a flush-outvalve, even if it is also used as a supply line.Seasonal systems do not use flush lines; theirtapes last only a season or two before needing to bereplaced. The drip lines may be connected to themanifold in several ways as shown in Figure 2.The manifold can be placed at the soil surface orburied. B-61517/04Installing a Subsurface DripIrrigation System for Row CropsJuan Enciso**Assistant Professor and Extension Agricultural Engineer,The Texas A&M University System.Figure 1. Typical layout of a drip irrigation system.MainField blockFlushingvalveValveFlushingmanifoldWatersourceSupplyingmanifoldLateralTape injectionThe injector consists of a roll that holds the tapeand a shank that opens the soil to bury the tape(Figs. 3 and 4). As the shank opens the soil, thetape is guided into the soil, usually through acurved pipe mounted behind the shank. Theshank must be durable enough to resist theimpact of rocks and other obstructions in the soil.The pipe that is mounted behind the shank shouldbe smooth and curved so it does not tear the tape.Drip line injection is shown in Figures 4 and 5.The steps for injecting the tape are:1. Mark the locations where the manifold andflush lines will be installed, using flags orlines of gypsum on the field.2. If the tape will be more than 8 inches deep orthe soil is rocky, pre-rip the rows using theshank alone without the tape. Pre-rippingmakes depth and spacing more uniform andhelps to clear away rocks that could damagethe tape. Pre-ripping is not necessary on eas-ily plowed fields.A) Manifold lying above the soil surface connecting one drip line.B) Manifold below the surface connecting one drip line.C) Manifold below the surface connecting two drip lines.Figure 2. Typical connections from manifold to drip lines or lat-erals. In this case the manifold is connected to the drip line witha stainless steel wire (there are many ways to connect it). Soil surfaceSoil surfaceSoil surfaceDrip lineTubing2 to 4 inchesDrip line14 to 24inches12 inches12 to 16inches10 to 12 inchesStainless steel wirePolythylenehose Drip linePVC pipeCemented saddleFigure 4. Installing the drip tape.Figure 3. Toolbars with drip tape injector.3. Be extremely careful not to cut the tapewhen unwrapping the plastic that covers theroll. (Sometimes the unwrapping is donewith a knife.) Careless or rough handling ofthe tape may lead to major leaks after instal-lation. 4. Lay the tape down with the emitters facingupward to avoid soil plugging. The rolls haveindicators showing the direction of the emit-ters.5. Just before lowering the shank, anchor thetape temporarily by hand or with a stake soit can be pulled into the soil. Stakes can bemade of welding rods or rigid wire (Fig. 4).6. The depth of the tape will depend on thecrop. Tape has been installed 12 to 14 inchesdeep for permanent SDI systems in cropssuch as cotton and alfalfa in the St.Lawrence, Trans-Pecos and Lubbock areas.Figure 6. Drip line splicing.Figure 5. Changing a roll of drip tape in the middle of the field.In the Lower Rio Grande Valley, tape hasbeen installed 2 to 6 inches deep for veg-etable crops such as onions and melons.Check to see that the tape is at the correctdepth and adjust the control roller if neces-sary.7. If the drip tape runs out in the middle of thefield it must be spliced (Figs. 5 and 6).  A 3-to 4-inch-long PVC tube can be used to splicethe old and new rolls together by securingthe tape to the ends of the tube using twostainless steel wires or special connections.   TrenchingTrenching may be necessary for mainlines,manifolds and flush lines. Manifolds and flushlines sometimes can be installed above the soilsurface, with a trench only for the mainline.Trenching can be done with a rotary trencher or abackhoe. A rotary trencher is recommended. Thesteps are as follows:1. Before trenching,pack the tape on thefield with a tractor,passing a wheel oneach side of thetape. (Fig. 7)2. Trenches should be2 feet wide or thesize of the bucket onthe backhoe. Thetrenches for thesubmains should beat least 16 inchesbelow the depth ofthe drip line and 1foot below the flush-ing line.3. Expose the tapefrom the ditch form-ing a triangle (Fig.8). Leave enoughspace to work withthe hands and tiethe drip line to thePVC pipe.4. Level and pack the ditch bottoms with soilthat falls from exposing the tape.5. Place some flags where each station ends.Splicing with connectionsConnector TapeWire tiesSplicing with wire tiesRigid tubeTapeFigure 7. Pack the soil with atractor tire on each side ofthe ditch.DitchFigure 8. Cross-section of thedrip tape connection to thePVC manifold.Figure 9. Drilling the manifold (A), inserting the grommet and the PVC hose (B), and connecting the PVC hose to the drip tape (C).AConnecting drip lines withmanifolds and flush linesIf manifolds and flush lines are below the soilsurface:There are several ways to make the connections.The following example uses grommets and barbfittings. 1. Drill a hole in the top of the manifold or flushline just where the tape is to be connected.(Figs. 9A and B). Use a 13/16-inch drill bit for#700 grommets (1-inch or 7/8-inch tape). Usea 9/16-inch drill bit for #400 grommets (5/8-inch tape).2. Clean the hole with a knife to remove allplastic residue. This plastic could produceleaks later in the season. 3. Insert the grommets in the hole.4. Pre-assemble the insertion to the PVC hose,using glue.5. Soak the insertion with soapy water so it willfit easily into the grommet.6. Insert the PVC hose into the tape, being care-ful not to bend the hose. 7. Tie a stainless steel wire around the tape(Fig. 9C).If submains and flush lines are above the soilsurface:The most common connection method is toinsert small-diameter PE tubing (0.188 to 0.35inches outside diameter) into the PVC, PE or layflat hose as shown in Figure 10A. A hole is thenmade on the drip line and the tubing is inserted inthe drip line. The tubing is attached to the dripline with a piece of folded tape. Another method isto use connections as shown in Figure 10b. Back-fillingRun each station for 4 hours and check for leaks.If there are leaks in the middle of the field, make ahole and splice the tape. If there is a leak in themanifold, the connection between the tape andmanifold needs to be redone or the plastic rem-nants need to be removed from the hole drilled inFigure 10. Connecting the drip tape to a manifold above the soilsurface with tubing (A) and with a fitting (B).B CABthe manifold. If there are no leaks, GENTLY pushsome loose soil into the ditch. Then add water tothe ditch so the soil will settle around the pipe tohold it and prevent it from moving. Do not movetoo much soil at once, as this can damage rigid pipeand connections. Pack the soil, then add more soiland water until the ditch is filled.Installing filtration equipmentThe filters should be installed over solid sur-faces, preferably concrete bases. A typical set up ofthe filtering equipment and its com-ponents is shown in Figures 11 and12. Filters remove the solid mattersuspended in the water to keep thedrip emitters from clogging. The mostcommon filtration size for subsurfacedrip irrigation is 200-mesh (200 open-ings per inch), which represents anopening of about 0.003 inches (0.076mm). Centrifugal filters, media orsand filters, and screen and disk filters are com-monly used, often in combination. For example, ifwater comes from an aquifer and some sand isbeing pumped, a centrifugal filter can be used totrap the sand, followed by a disk or sand media fil-ter. When water comes from a canal, it is commonto have both a media filter and a screen filter.Media filters need the most adjustment duringinstallation. Media filters consist of several tanksthat filter the water, and each tank needs to beback-flushed. This is done by passing clean waterthrough a tank in a reverse direction; the cleanFigure 11. Typical layout of the pumping station showing the filtering equipment.Figure 12. Filtration and back-flushing process.Fertilizer TankChemicalInjectorAir ValveBack-FlushFlow RateAdjustment ValveMaster ValveValve forFieldBlock 2LateralsSubmain(Manifold)Valve forField Block 1Pressure GaugeFilter StationPressureGaugeButterflyValveAutomaticLow PressureDrainCheck ValveFlow MeterPumpControllerVacuumReliefValveFiltration Process Back-Flushing ProcessBack-FlushValveInletInletOutletOutletwater comes from the other tanks that are notbeing back-flushed (Fig. 13). Tanks must be back-flushed when they are dirty, a condition that isusually indicated by an increase of pressure ofabout 10 psi.A sand media filter has some pressureloss–about 3 to 5 psi. Incorrect installation canincrease the loss to about 10 to 25 psi. Follow thesesteps to install a sand media filter:1. Order only pre-washed gravel.2. Install the gravel and the sand at the depthsrecommended by the manufacturer.3. Close all the valves downstream of the tanks(the back-flush valve).4. Open the main valve (butterfly valve).5. Open completely the back-flush valve of oneof the media tanks. Then open the back-flushflow rate adjustment valve slowly. Remem-ber that the back-flush flow rate adjustmentvalve should be calibrated just one time. Theback-flush flow rate should be determinedfrom visual observation.• The back-flush flow rate should be suffi-cient to expand the media bed and separatethe sand into individual particles. Thesmaller particles and those with lighterspecific gravity than the media need to becarried out of the tank.• The back-flush flow rate should not beexcessive to limit the amount of sandremoved from the tank. The first time atank is back-flushed it is normal to removesome sand. Use a 100-mesh screen at thedischarge to catch the sand discharged.6. Repeat the process, opening the back-flushvalve of each tank.7. Adjust the frequency and the time of theback-flushing operation. It is important toback-flush at least once per day and to con-trol the back-flushing automatically by trig-gering it with a differential pressure switch.This switch is usually set to start when thedifferential pressure increases to 5 to 8 psi.Figure 13. Filtration equipment.This material is based upon work supported by the Rio Grande Basin Initiative of the Cooperative State Research,Education and Extension Service, U.S. Department of Agriculture under Agreement No. 2001-45049-01149.

Installing a Subsurface Drip Irrigation System for Row Crops

Texas A&M University

The success of a subsurface drip irrigation (SDI)
system for row crops depends on its design, instal-
lation, operation, management and maintenance.
All phases are equally important. This publication
describes the components and installation of an
SDI system. Steps in the installation process are:
• tape injection;
• trenching;
• installing the mainlines, manifolds (sub-
mains) and flush lines;
• connecting the tape with the manifolds and
flush lines;
• back filling; and
• installing filtration equipment. 
Components of the
irrigation system
The main components of an irrigation system
are the filters, mainlines, manifolds (submains),
field blocks, flush lines, drip lines (laterals) and
accessories (Fig. 1).  
All the drip lines (laterals) connected to the
same submain make up a field block. Several field
blocks can be grouped together as one station and
operated simultaneously. Water is supplied to drip
lines in the field blocks by the manifold (submain).
In some permanent systems, the drip lines are also
connected to a flush line so that accumulated sed-
iments can be flushed from the drip lines using a
single valve. The flush line is also called a collector
line. In some field blocks, particularly those with
longer lateral lengths (more than 200 m), the flush
line may also be connected to the mainline by a
separate valve and manifold, so that water can be
supplied to both ends of the drip line. This pre-
vents excessive pressure loss in longer drip lines.
The flush line should always contain a flush-out
valve, even if it is also used as a supply line.
Seasonal systems do not use flush lines; their
tapes last only a season or two before needing to be
replaced. The drip lines may be connected to the
manifold in several ways as shown in Figure 2.
The manifold can be placed at the soil surface or
buried. 
B-6151
7/04
Installing a Subsurface Drip
Irrigation System for Row Crops
Juan Enciso*
*Assistant Professor and Extension Agricultural Engineer,
The Texas A&M University System.
Figure 1. Typical layout of a drip irrigation system.
Main
Field block
Flushing
valve
Valve
Flushing
manifold
Water
source
Supplying
manifold
Lateral
Tape injection
The injector consists of a roll that holds the tape
and a shank that opens the soil to bury the tape
(Figs. 3 and 4). As the shank opens the soil, the
tape is guided into the soil, usually through a
curved pipe mounted behind the shank. The
shank must be durable enough to resist the
impact of rocks and other obstructions in the soil.
The pipe that is mounted behind the shank should
be smooth and curved so it does not tear the tape.
Drip line injection is shown in Figures 4 and 5.
The steps for injecting the tape are:
1. Mark the locations where the manifold and
flush lines will be installed, using flags or
lines of gypsum on the field.
2. If the tape will be more than 8 inches deep or
the soil is rocky, pre-rip the rows using the
shank alone without the tape. Pre-ripping
makes depth and spacing more uniform and
helps to clear away rocks that could damage
the tape. Pre-ripping is not necessary on eas-
ily plowed fields.
A) Manifold lying above the soil surface connecting one drip line.
B) Manifold below the surface connecting one drip line.
C) Manifold below the surface connecting two drip lines.
Figure 2. Typical connections from manifold to drip lines or lat-
erals. In this case the manifold is connected to the drip line with
a stainless steel wire (there are many ways to connect it). 
Soil surface
Soil surface
Soil surface
Drip lineTubing
2 to 4 inches
Drip line
14 to 24
inches
12 inches
12 to 16
inches
10 to 12 inches
Stainless steel wire
Polythylene
hose Drip line
PVC pipe
Cemented saddle
Figure 4. Installing the drip tape.
Figure 3. Toolbars with drip tape injector.
3. Be extremely careful not to cut the tape
when unwrapping the plastic that covers the
roll. (Sometimes the unwrapping is done
with a knife.) Careless or rough handling of
the tape may lead to major leaks after instal-
lation. 
4. Lay the tape down with the emitters facing
upward to avoid soil plugging. The rolls have
indicators showing the direction of the emit-
ters.
5. Just before lowering the shank, anchor the
tape temporarily by hand or with a stake so
it can be pulled into the soil. Stakes can be
made of welding rods or rigid wire (Fig. 4).
6. The depth of the tape will depend on the
crop. Tape has been installed 12 to 14 inches
deep for permanent SDI systems in crops
such as cotton and alfalfa in the St.
Lawrence, Trans-Pecos and Lubbock areas.
Figure 6. Drip line splicing.
Figure 5. Changing a roll of drip tape in the middle of the field.
In the Lower Rio Grande Valley, tape has
been installed 2 to 6 inches deep for veg-
etable crops such as onions and melons.
Check to see that the tape is at the correct
depth and adjust the control roller if neces-
sary.
7. If the drip tape runs out in the middle of the
field it must be spliced (Figs. 5 and 6).  A 3-
to 4-inch-long PVC tube can be used to splice
the old and new rolls together by securing
the tape to the ends of the tube using two
stainless steel wires or special connections.   
Trenching
Trenching may be necessary for mainlines,
manifolds and flush lines. Manifolds and flush
lines sometimes can be installed above the soil
surface, with a trench only for the mainline.
Trenching can be done with a rotary trencher or a
backhoe. A rotary trencher is recommended. The
steps are as follows:
1. Before trenching,
pack the tape on the
field with a tractor,
passing a wheel on
each side of the
tape. (Fig. 7)
2. Trenches should be
2 feet wide or the
size of the bucket on
the backhoe. The
trenches for the
submains should be
at least 16 inches
below the depth of
the drip line and 1
foot below the flush-
ing line.
3. Expose the tape
from the ditch form-
ing a triangle (Fig.
8). Leave enough
space to work with
the hands and tie
the drip line to the
PVC pipe.
4. Level and pack the ditch bottoms with soil
that falls from exposing the tape.
5. Place some flags where each station ends.
Splicing with connections
Connector Tape
Wire ties
Splicing with wire ties
Rigid tube
Tape
Figure 7. Pack the soil with a
tractor tire on each side of
the ditch.
Ditch
Figure 8. Cross-section of the
drip tape connection to the
PVC manifold.
Figure 9. Drilling the manifold (A), inserting the grommet and the PVC hose (B), and connecting the PVC hose to the drip tape (C).
A
Connecting drip lines with
manifolds and flush lines
If manifolds and flush lines are below the soil
surface:
There are several ways to make the connections.
The following example uses grommets and barb
fittings. 
1. Drill a hole in the top of the manifold or flush
line just where the tape is to be connected.
(Figs. 9A and B). Use a 13/16-inch drill bit for
#700 grommets (1-inch or 7/8-inch tape). Use
a 9/16-inch drill bit for #400 grommets (5/8-
inch tape).
2. Clean the hole with a knife to remove all
plastic residue. This plastic could produce
leaks later in the season. 
3. Insert the grommets in the hole.
4. Pre-assemble the insertion to the PVC hose,
using glue.
5. Soak the insertion with soapy water so it will
fit easily into the grommet.
6. Insert the PVC hose into the tape, being care-
ful not to bend the hose. 
7. Tie a stainless steel wire around the tape
(Fig. 9C).
If submains and flush lines are above the soil
surface:
The most common connection method is to
insert small-diameter PE tubing (0.188 to 0.35
inches outside diameter) into the PVC, PE or lay
flat hose as shown in Figure 10A. A hole is then
made on the drip line and the tubing is inserted in
the drip line. The tubing is attached to the drip
line with a piece of folded tape. Another method is
to use connections as shown in Figure 10b. 
Back-filling
Run each station for 4 hours and check for leaks.
If there are leaks in the middle of the field, make a
hole and splice the tape. If there is a leak in the
manifold, the connection between the tape and
manifold needs to be redone or the plastic rem-
nants need to be removed from the hole drilled in
Figure 10. Connecting the drip tape to a manifold above the soil
surface with tubing (A) and with a fitting (B).
B C
A
B
the manifold. If there are no leaks, GENTLY push
some loose soil into the ditch. Then add water to
the ditch so the soil will settle around the pipe to
hold it and prevent it from moving. Do not move
too much soil at once, as this can damage rigid pipe
and connections. Pack the soil, then add more soil
and water until the ditch is filled.
Installing filtration equipment
The filters should be installed over solid sur-
faces, preferably concrete bases. A typical set up of
the filtering equipment and its com-
ponents is shown in Figures 11 and
12. Filters remove the solid matter
suspended in the water to keep the
drip emitters from clogging. The most
common filtration size for subsurface
drip irrigation is 200-mesh (200 open-
ings per inch), which represents an
opening of about 0.003 inches (0.076
mm). Centrifugal filters, media or
sand filters, and screen and disk filters are com-
monly used, often in combination. For example, if
water comes from an aquifer and some sand is
being pumped, a centrifugal filter can be used to
trap the sand, followed by a disk or sand media fil-
ter. When water comes from a canal, it is common
to have both a media filter and a screen filter.
Media filters need the most adjustment during
installation. Media filters consist of several tanks
that filter the water, and each tank needs to be
back-flushed. This is done by passing clean water
through a tank in a reverse direction; the clean
Figure 11. Typical layout of the pumping station showing the filtering equipment.
Figure 12. Filtration and back-flushing process.
Fertilizer Tank
Chemical
Injector
Air Valve
Back-Flush
Flow Rate
Adjustment Valve
Master Valve
Valve for
Field
Block 2
Laterals
Submain
(Manifold)
Valve for
Field Block 1
Pressure Gauge
Filter Station
Pressure
Gauge
Butterfly
Valve
Automatic
Low Pressure
Drain
Check Valve
Flow Meter
Pump
Controller
Vacuum
Relief
Valve
Filtration Process Back-Flushing Process
Back-Flush
Valve
InletInlet
OutletOutlet
water comes from the other tanks that are not
being back-flushed (Fig. 13). Tanks must be back-
flushed when they are dirty, a condition that is
usually indicated by an increase of pressure of
about 10 psi.
A sand media filter has some pressure
loss–about 3 to 5 psi. Incorrect installation can
increase the loss to about 10 to 25 psi. Follow these
steps to install a sand media filter:
1. Order only pre-washed gravel.
2. Install the gravel and the sand at the depths
recommended by the manufacturer.
3. Close all the valves downstream of the tanks
(the back-flush valve).
4. Open the main valve (butterfly valve).
5. Open completely the back-flush valve of one
of the media tanks. Then open the back-flush
flow rate adjustment valve slowly. Remem-
ber that the back-flush flow rate adjustment
valve should be calibrated just one time. The
back-flush flow rate should be determined
from visual observation.
• The back-flush flow rate should be suffi-
cient to expand the media bed and separate
the sand into individual particles. The
smaller particles and those with lighter
specific gravity than the media need to be
carried out of the tank.
• The back-flush flow rate should not be
excessive to limit the amount of sand
removed from the tank. The first time a
tank is back-flushed it is normal to remove
some sand. Use a 100-mesh screen at the
discharge to catch the sand discharged.
6. Repeat the process, opening the back-flush
valve of each tank.
7. Adjust the frequency and the time of the
back-flushing operation. It is important to
back-flush at least once per day and to con-
trol the back-flushing automatically by trig-
gering it with a differential pressure switch.
This switch is usually set to start when the
differential pressure increases to 5 to 8 psi.
Figure 13. Filtration equipment.
This material is based upon work supported by the Rio Grande Basin Initiative of the Cooperative State Research,
Education and Extension Service, U.S. Department of Agriculture under Agreement No. 2001-45049-01149.


English

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Installing a Subsurface Drip Irrigation System for Row Crops

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Installing a Subsurface Drip Irrigation System for Row Crops

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