INSTALLATION ISSUES FOR
By F. R. Lamm, G. A. Clark, M.
Yitayew, R. A. Schoneman, R. M. Mead, A. D. Schneider
This paper discusses issues that should be considered by
manufacturers, distributors, and end users for installation and subsequent operation of
subsurface drip irrigation (SDI) systems. These issues include factors associated with
quality control during the manufacturing and installation processes that can be much more
crucial for SDI installations than for surface drip installations. Even small failures in
SDI systems are troublesome because of the increased difficulty associated with repairs
below the soil surface. Experiences and concerns that have developed from SDI research
installations in Kansas, Texas, Arizona, Colorado, and California will be presented.
In the future, SDI probably will have an increased focus on
lower value crops, which do not have the income potential to help "write off"
system failures. Early consideration of the special design and installation requirements
of SDI by manufacturers, distributors, consultants, and end users can minimize the
negativism of avoidable system failures and advance early adoption of this useful
SUITABILITY OF DESIGN
A successful SDI system begins with an appropriate hydraulic
network design and selection of appropriate water treatment system (filtration and
chemical amendment). These are not focuses of this paper, but because of their importance,
they are discussed briefly. Disregarding the suitability of the design and filtration
system will likely result in a system that is costly in both time and money to operate and
will likely increase the chance of system failure.
Design characteristics such as dripline spacing,
crop/dri-pline orientation, emitter spacing, installation depth, and dripline flow rates
are site specific and governed by soil type, climate, crop, and other factors.
Consult-ants, distributors, and end users should remember that these issues are not
generic and that appropriate technology in one region may not be appropriate in another
region. Consultants, distributors, and end users instead should strive to understand these
issues from a conceptual approach. These design characteristics are very important to the
success of the system and should not be ignored. Consistent dripline spacing,
crop/dripline orientation, and depth of placement are important in managing salinity and
water redistribution and in minimizing tillage damage to the driplines (Ayars et al. 1995;
Kruse and Israeli, 1987; Lamm et al. 1997). Major factors related to dripline spacing
include the lateral extent of the crop root zone, lateral extent of soil water
redistribution, and the within-season precipitation. Deeper installation depths reduce the
potential for soil evaporation and also allow for a wider range of tillage practices.
However, deeper installations can limit effectiveness of the SDI system for seed
germination, restrict the availability of surface-applied nutrients, and result in high
salinity levels in surface soils when used with saline water supplies. Dripline flow rates
must be sufficient to provide for the water needs of the crop. Some designers prefer
higher capacity driplines, because they are less subject to plugging and allow more
flexibility in irrigation scheduling. However, higher capacity driplines typically require
shorter lengths of run to maintain acceptable uniformity and can increase
"surfacing" of water on some soil types. Resource books that discuss many of the
important concepts for SDI are available for additional information (Jorgenson and Norum,
1992; Schwankl et al. 1993; Hanson et al. 1994; Burt and Kasapligil, 1992). It should also
be noted that an improperly designed SDI system is less forgiving than an improperly
designed surface irrigation or center pivot sprinkler irrigation system. Water
distribution problems associated with an improperly designed SDI system may be difficult
or impossible to correct.
The filtration system is one of the most important
compon-ents of the SDI system. Its operation and maintenance must be well understood by
the end user to help ensure its longevity. Many different types of filtration systems are
used with SDI systems, and their design and specifications are based upon the
characteristics of the water source and emitters. Improper filter selection can result in
a SDI system which is difficult to maintain and a system that is prone to failure. In
addition to the filtration system, a water treatment system generally will be required to
inject chemicals, to prevent emitter plugging, and to possibly renovate partially plugged
A flushing system is recommended at the distal end of the
dripline laterals to assist in removing sediment and other materials that can accumulate
in the driplines during the irrigation season. This is used in addition to a proper
filtration system. All of the distal ends of the driplines in a zone can be connected to a
common submain or header, which is called the flushline. This technique allows flushing
from one central point. Two other distinct advantages exist for this closed-loop method.
If a dripline becomes plugged or partially plugged, pressurized water will be provided
below the plugged area by the interconnected flushline. Additionally, if a break in the
dripline occurs, positive water pressure on both sides of the break will limit sediment
intrusion into the line.
Seven other design components critical to successful use of
SDI are worth noting. Pressure regulation is necessary to ensure uniform water
distribution to the various points in the SDI system. Primary pressure relief must be
provided to prevent excessive pressure, which could cause component failure or bursting of
the driplines. Pressure gages should be installed on riser pipes at each of the four
corners of the closed-loop zone. Recorded pressures from these gages and flow rates from
the system flowmeter can be compared from one event to the next to help reveal system
performance problems. Checkvalves, air vents, and vacuum breakers may be required at
various points in the system to prevent back-siphoning of chemically treated water into
the water supply and also to prevent ingestion of soil into the driplines at system
End users should take the responsibility to ask questions of
knowledgeable consultants, distributors and other current users of SDI systems to avoid
installation problems. Substantial knowledge is available from experts, but it is not
readily available in written form as a complete source book of information on SDI
installation. This is particularly true for deeper dripline placements used in permanent
systems. Burt and Kasapligil (1992) discuss California perspectives associated with the
shallow installation issues for 7- to 20-cm dripline depths. In the absence of adequate
knowledge and regional experiences, the end user should use a go-slow approach to SDI
development. Most manufacturers, distributors, and consultants recommend that users start
their SDI experience with a small area to limit their financial risk and to allow for a
slower-paced learning curve.
COMPONENT SELECTION AND COMPATIBILITY
There are numerous manufacturers of SDI components and
obtaining compatible components for a SDI system is not always a straightforward process.
Competition among manufacturers for market niches can be a double edged sword. Although a
myriad of new and innovative products are available, their use can lead to confusion and
misapplication by the end user.
Connecting the dripline to the submain or header appears to
be the most troublesome point in SDI installations, complicated by the fact that it is
usually a double connection with a supply tube providing the transition. Copeland and
Yitayew (1990) reported incompatibility between dripline and dripline connectors as one of
the main problems encountered on a research SDI system at the University of Arizona. Much
of this problem seemed to stem from the fact that the SDI system installation was split
into bids from two companies that did not always match components. This problem would have
been fairly inconsequential if the system had not been subsurface. Manufacturers might
help to eliminate problems such as these by explicitly stating the brand names and
specifications of known compatible products in their product literature. Color coding of
connectors to a particular tubing size, tubing manufacturer, or tubing style might be
another way to enhance compatibility. Some product literature uses terms like
"universal" or "generic" to describe compatibility, when new products
are being introduced continuously. Dealers and distributors can provide help by suggesting
brand name products and specific part numbers. They should also educate end users about
possible component incompatibilities caused by various dripline wall thicknesses and
Couplers that use rotation of a threaded collar to create an
interference fit between the connector and thin-wall drip tape can cause problems.
Although these couplers create a watertight seal when properly connected, variability in
the squareness of the dripline cut; dripline temperature and dryness; and the installer's
experience, fatigue, and hand strength can have a large influence on the success of the
final connection. Making the connection for surface systems is very different than making
the connection in a trench or hole that may 45 to 60 cm below the soil surface.
Manufacturers might consider developing new, reliable, watertight, foolproof,
easy-to-install connectors for SDI systems. The higher costs of such connectors might be
buffered by labor savings in ease-of-use and in fewer repairs of leaking connections. End
users also must use quality control because of the variability among installers. Checking
all connections for water tightness before backfilling is very important.
Compatibility of solvent cements and the associated
components has created problems in research installations in Texas and California.
Bondable saddles installed on the submain seem to be one of the major points of concern.
Although some product literature indicates that heavy body cements should be used,
manufacturers and distributors might enhance this point by noting it on or in each box of
saddles distributed. Maintaining the saddles in the proper position with sufficient
pressure until adequate bonding has occurred is a problem in subsurface situations. This
problem appears to be resolved best by securing the saddle with hose clamps, wire, tape,
or heavy string. However, this can be costly or time consuming. Proper care also must be
used when drilling the pilot hole for the saddle (Schoneman et al. 1992). Manufacturers
need to clearly state the type and size of drill bit to be used for their saddles and
inserts. Again, pressurized checking of the system before backfilling is important.
Installation guides published by some of the dripline
manufacturers show numerous ways of making a connection or dripline closure. It would be
useful if the literature could be expanded to discuss the pros and cons of the different
connection methods and perhaps even suggest preferred or appropriate methods for SDI
systems. For example, the method for drilling an undersized hole in the PVC submain for an
interference fit with the supply tube is inexpensive but does require more care by the
installer. Installer errors related to these interference connections were listed as a
major source of problems in a research SDI system in Colorado (Kruse and Israeli, 1987).
Leaks at the dripline con-nection also were listed as the greatest problem in a 100-ha
strawberry operation in California (Feistel, 1992). Having a water-efficient and uniform
irrigation system is difficult when it is full of leaks.
Manufacturers should offer optional availability of
custom-length dripline rolls to accommodate a multiple of the end user's field length,
thus minimizing the number of in-field splices. Splicing one reel of dripline to the next
is critical, because the splices are buried before they can be tested. These splices are
further away from field margins where they are difficult to repair and harder to detect
under a growing crop. Dripline manufacturers need to develop a foolproof connection for
this purpose. The connection needs to pass undamaged through the chisel injection tube as
the dripline is installed into the ground.
Manufacturing defects in driplines were listed as a major
problem in 2 of 20 systems in California surveyed by Feistel (1992). A small amount of
defective dripline without emitters also was encountered in a research SDI installation in
California. These occurrences are probably quite rare, but problems associated with
defects in a SDI system are time consum-ing to diagnose and repair. Dripline defects in a
SDI system might be noticed first when it is too late (i.e., when crop yields are
reduced). As was previously mentioned, the repair or replacement of a surface installed
dripline is much easier.
INSTALLATION OF SYSTEM
A few dripline injector systems are commercially available
for plow-ing in the dripline. However, the suitability of these implements for a
particular soil type and installation depth appears to be an unanswered question. Typical
draft requirements and installation speeds should be specified for various soil types and
operating depths, as well as the maximum allowable safe draft to prevent injector
equipment failure (shear bolt strength ratings). Equipment options and their functions
should be listed clearly in the product literature. Dripline reels and rolls need to have
standardized hubs to accommodate equipment from different manufacturers and should allow
for easy changing of spools in the field. The cardboard roll retainers sometimes will
allow the dripline to slide down to the hub and stretch or tear. Manufacturers have
suggested sandwiching the cardboard retainers between plywood, which would help with clean
spooled dripline, but does not solve the problem of pinched tape that occasionally occurs
on rolls directly from the manufacturer. Recyclable, rigid, plastic, roll retainers could
be offered as an option.
The dripline connection to the submain already has been noted
as a major problem area. End users should pay particular attention to this area by
selecting a methodology that they can use successfully and also by selecting appropriate
skilled workers for this task. An additional installation problem is kinked supply tubes
which can occur because of improper measurements, placements, or during backfilling. Use
of the 13 to 19 mm flexible PVC tubing instead of the more conventional polyethylene
tubing as the supply tube may help to avoid kinked tubes. Care should be during the
dripline injection operation to ensure that the installation depth at the location of the
submains is at the same uniform depth as the general field. Consistent installation depth
allows for uniformity in length and placement of the supply tube, and allows for uniform
tillage depths within the general field and the field margins.
Currently, installation generally is performed by the end
user. However, this convention is slowly changing and, with time, dealers who can provide
a turn-key system will evolve. Manufacturers should seek to nurture and encourage this
process, while at the same time providing improved educational materials for those who
want to install these systems on their own.
Installation practices for SDI systems need to be viewed with
regard to their effect on the long-term operation of the system (Camp et al. 1997). For
example, a 40-cm wide trench with the excavated dirt moved away from the trench is more
expensive than a narrower trench with loose soil mounded along the sides. However,
installers can make better quality connections inside a cleaner, wider trench and the
total cost of the installation will likely be less since fewer repairs will be required.
Another cost-saving technique is the use of stainless steel wire ties in dripline splices.
They are initially more expensive but will not rust out nearly as soon as the less
expensive black steel wire ties. Effective testing and quality control procedures for
checking all connections before backfilling are other examples where the added effort will
be cost effec-tive in the long run.
The potential for SDI technology to move into the agronomic
field crop market is increasing. However, cost/profit margins are much lower within these
production systems as compared to horticultural crop systems. It is reasonable and
justified to minimize SDI system investment costs whenever possible and practical.
However, a quality installation that can be operated and maintained easily must be
accepted as less expensive than a minimal substandard design that requires frequent and
possibly frustrating repairs. Successful adoption of SDI technology will require durable,
compatible, and user-friendly components; local support for design, installation, and
service; and continuing educational programs on proper operational and management
procedures. Suc-cess will depend on a heightened awareness and commitment to quality
similar to those required in other advanced technologies.
Ayars, J. E., C. J. Phene, R. A. Schoneman, B. Meso, F. Dale,
and J. Penland. 1995. Impact of bed location on the operation of subsurface drip
irrigation systems. Pages 141-146 in proceedings of the Fifth International
Microirrigation Congress, Orlando, FL., Apr. 2-6, 1995. Available from ASAE, St Joseph,
MI. 978 pp.
Burt, C. M. and D. Kasapligil. 1992. Permanent row crop drip
-- management and design (with a California emphasis). Published by Irrigation Training
and Research Center, California Polytechnic State University, San Luis Obispo, CA. 50 pp.
Camp, C. R., E. J. Sadler, and W. J. Busscher. 1997. A
comparison of uniformity measures for drip irrigation systems. Trans ASAE 40(4) (in
Copeland, R. D. and M. Yitayew. 1990. Evaluation of a
subsurface trickle irrigation system. Presented at the international winter meeting of the
American Society of Agricultural Engineers, Chicago, IL, Dec. 18-21, 1990. ASAE Paper No.
902531, ASAE, St. Joseph, MI. 9 pp.
Feistel, S. 1992. Senior project survey. Pages 20-24 in
Permanent row crop drip -- management and design (with a California emphasis). Published
by C. M. Burt and D. Kasapligil, Irrigation Training and Research Center, California
Polytechnic State University, San Luis Obispo, CA. 50 pp.
Hanson B., L. Schwankl, S. R. Graham and T. Pritchard. 1994.
Drip irrigation for row crops. Water management series publication number 93-05, Univ. of
California-Davis Cooperative Extension, Davis CA. 175 pp.
Jorgenson, G. S. and K. N. Norum. 1992. Subsurface drip
irrigation -- theory, practices and application. Conference proceedings sponsored by
California State University-Fresno and USDA ARS-Water Management Research Laboratory. CATI
Publication No. 92-1001, CSUF, Fresno CA. 212 pp.
Kruse, E. G. and I. Israeli. 1987. Evaluation of a subsurface
drip irrigation system. Presented at the international summer meeting of the American
Society of Agricultural Engineers, 1987. ASAE Paper No. 87-2034, ASAE, St. Joseph, MI. 21
Lamm, F. R., L. R Stone, H. L. Manges and D. M. O'Brien .
1997. Optimum lateral spacing for subsurface drip-irrigated corn. Trans ASAE 40(4) (in
Schoneman, R. A., H. I. Nightingale and B. Yarnell. 1992.
Subsurface drip installation. Presented at the international winter meeting of the
American Society of Agricultural Engineers, Nashville, TN, Dec. 15-18, 1992. ASAE Paper
No. 922552, ASAE, St. Joseph, MI. 6 pp.
Schwankl, L., B. Hanson, and T. Pritchard. 1993. Low volume
irrigation. Water management series publication number 93-03, Univ. of California-Davis
Cooperative Extension, Davis CA. 116 pp.
This material was first presented at the Irrigation
Association's 16th Annual International Irrigation Exposition and Technical Conference,
Phoenix, Arizona, November 12-14, 1995. Slight revisions were made in August 1997.
The authors are Freddie R. Lamm, Associate Professor,
Northwest Research-Extension Center, Kansas State University, Colby, KS., Email: firstname.lastname@example.org, Phone: 785-462-6281, Fax:
Gary A. Clark, Professor, Biological and Agricultural
Engineering, Kansas State University, Manhattan, KS;
Muluneh Yitayew, Associate Professor, Agricultural and
Biosystems Engineering, University of Arizona, Tucson, AZ;
Richard A. Schoneman, Agricultural Engineer, USDA-ARS Water
Management Research Laboratory, Fresno, CA;
Richard M. Mead, Technical Director, Agrilink International,
Arland D. Schneider, Agricultural Engineer, USDA-ARS
Conservation and Production Research Laboratory, Bushland TX.
This is contribution no. 98-4-A from the Kansas Agricultural
Experiment Station. Any opinions, findings, conclusions, or recommendations expressed in
this publication are those of the authors and do not necessarily reflect the views of the
U. S. Department of Agriculture, Kansas State University or the University of Arizona.