Irrigation: An Introduction
August 2006, June 2001
consider drip irrigation?
and design of a drip
of drip irrigation
In an effort to find an alternative method of
crops with high water demands in an arid region, we considered drip
irrigation. Drip irrigation is the slow, even application of low
pressure water to soil and plants using plastic tubing placed directly
at the plants root zone.
consider drip irrigation?
Drip irrigation can help you use water
well-designed drip irrigation system loses practically no water to
runoff, deep percolation, or evaporation. Drip irrigation reduces water
contact with crop leaves, stems, and fruit. Thus
conditions may be less favorable for the onset of diseases. Irrigation
scheduling can be managed precisely to meet crop demands, holding the
promise of increased yield and quality.
Growers and irrigation professionals often refer to
"subsurface drip irrigation," or SDI. When a drip tape or tube is
below the soil surface, it is less vulnerable to damage during
cultivation or weeding. With SDI, water use efficiency is
maximized because there is even less evaporation or runoff.
Agricultural chemicals can be applied more
drip irrigation. Since only the crop root zone is irrigated,
nitrogen already in the soil is less subject to leaching losses, and
applied fertilizer N can be used more efficiently. In the case of
insecticides, less product might be needed. Make sure the insecticide
is labeled for application through drip irrigation.
Additional advantages of drip irrigation include:
- Drip systems are
adaptable to oddly shaped fields or
those with uneven topography or soil texture; these
specific factors must be considered in designing the drip system. Drip
systems also can work well where other
irrigation systems are inefficient because parts of the field have
excessive infiltration, water puddling, or runoff.
- Drip irrigation can be
helpful if water is scarce or
expensive. Because evaporation, runoff, and deep percolation are
reduced and irrigation uniformity is improved, it is not necessary to
"over-water" parts of a field to adequately irrigate the more difficult
- Precise application of
nutrients is possible using drip
irrigation. Fertilizer costs and nitrate losses can be reduced.
Nutrient applications can be better timed to meet plants' needs.
- Drip irrigation systems
can be designed and managed so
that the wheel traffic rows are dry enough to allow tractor operations
at any time. Timely application of herbicides, insecticides, and
fungicides is possible.
- Proven yield and quality
responses to drip irrigation
have been observed in onion, broccoli, cauliflower, lettuce, melon,
tomato, and cotton.
- A drip irrigation system
can be automated. For an
example of automated drip irrigation, see the Malheur Experiment
Station's 1998 onion
drip irrigation trial results.
There are some disadvantages to drip irrigation. For
- Drip irrigation systems
typically cost $500 to $1,200 or
more per acre. Part of the cost is a capital investment useful for
several years, and part is annual. Systems can be more elaborate and
costly than they need to be. Growers new to drip irrigation might want
to start with a relatively simple system on a small acreage.
- Drip tape or tubing must
be managed to avoid leaking or
Drip emitters are easily plugged by silt or other particles not
filtered out of the irrigation water. Emitter plugging also can be
caused by algae growing in the tape or by chemical deposits at the
- You might need to redesign your weed
Drip irrigation might be unsatisfactory if herbicides need sprinkler
irrigation for activation. However, drip irrigation can
enhance weed control in arid climates by keeping much of the soil
surface dry. Tape
depth must be chosen carefully for compatibility with operations such
as cultivation and weeding.
- Drip tape causes extra
cleanup costs after harvest.
You'll need to plan for drip tape disposal, recycling or reuse.
Despite all of drip irrigation's potential benefits,
converting to drip irrigation can increase production costs, especially
where an irrigation system already is in place. Ultimately, there
must be an economic advantage to drip irrigation to make it worthwhile.
and design of a drip irrigation system
A wide range of components and system design options
available. The Drip
Directory lists equipment and suppliers. Drip tape varies greatly
in its specifications, depending on the manufacturer and its use (Table
1). The distribution system, valves, and pumps must match the supply
requirements of the tape. Tape, depth of tape placement, distance
between tapes, emitter spacing and flow, and irrigation management all
must be chosen carefully based on crop water requirements and the
soil's properties. Drip tubing rather than drip tape is usually used
for perennial crops such as grapes or poplar trees.
Table 1. Drip tape
|| 4, 6, 8, 10, 15
|2, 4, 8, 9, 12, 16, 24
||0.125 - 0.65
Man. and Eng. Inc.
|| 5, 6,
7-8, 10, 15
||4 1/4, 8
1/2, 12 3/4, 17 1/4
||5/8, 7/8, 1
| 6, 8,
10, 12, 15
0.40, 0.60, 1.00
|5/8, 7/8, 1
|| 6, 8,
10, 13, 15
0.24, 0.33, 0.48,
|5/8, 3/4, 7/8
|| 5, 6,
8, 10, 13,
|4, 8, 12,
0.20 0.24, 0.27,
| 4, 5,
6, 7, 8, 10, 15, 20
|4, 6, 8, 12,
16, 18, 24
0.27, 0.28, 0.34, 0.40, 0.44, 0.45, 0.67
|5/8, 7/8, 1
| 4, 6,
|4, 8, 12,
0.20, 0.27, 0.34
The wetting pattern of water in the soil from the
irrigation tape must reach plant roots. Emitter spacing depends on the
crop root system and soil properties. Seedling plants such as onions
have relatively small root systems, especially early in the
Design must take into account the effect of the
contour on pressure and flow requirements. Plan for water distribution
uniformity by carefully considering the tape, irrigation lengths,
topography, and the need for periodic flushing of the tape. Design
vacuum relief valves into the system.
When designing a drip system, first identify fairly
similar Irrigation zones.
are based on factors such as topography, field length, soil texture,
optimal tape run length, and filter capacity. Many irrigation system
suppliers use computer programs to easily analyze these factors and
design drip systems. Once the zones are assigned and the drip system is
designed, it is possible to schedule irrigations to meet the unique
needs of the crop in each zone.
Consider power and water source limitations. Have
analyzed by a laboratory that is qualified to evaluate emitter plugging
hazards. Water quality might create limitations and increase system
costs. Filters must be able to handle worst-case scenarios.
Finally, be sure to include both injectors for
and flow meters to confirm system performance.
Filters and Pumps
Every trickle counts when you are battling a water shortage. An
ineffective or improperly managed filter station can waste a lot of
water and threaten a drip system's fitness and accuracy.
In the western U.S., sand media filters have been used extensively for
micro irrigation systems. Screen filters and disk filters are common as
alternatives or for use in combination with sand media filters.
Sand media filters provide filtration to 200 mesh, which is
to clean surface water and water from open canals for drip irrigation.
These water sources pick up a lot of fine grit and organic material,
which must be removed before the water passes through the drip tape
Sand media filters are designed to be self-cleaning through a
"backflush" mechanism. This mechanism detects the drop in pressure due
to the accumulation of filtered particles. It then flushes water back
through the sand to dispose of clay, silt, and organic particles.
Sand used for filters should be between size 16 and 20 to prevent
excess back flushing. To assure enough clean water for back flushing,
several smaller sand media filters are more appropriate than a single
large sand media filter (Gleski, 2003).
In addition to a sand media filter, a screen filter can be used as a
prefilter to remove larger organic debris before it reaches the sand
media filter, or as a secondary filter before the irrigation water
enters the drip tube (Figure 1). For best results, filters should
remove particles four times smaller than the emitter opening, as
particles may clump together and clog emitters. Screen filters can act
a safe guard if the main filters fail, or may act as the main
filter if a sufficiently clear underground water source is used.
Figure 1. Drip irrigation
systems with a prefilter, pump station with backflow prevention, and
chemical injection site. The chemical injection site can be before or
after the main filter station. A pressure control valve is recommended
to adjust the water pressure as desired before it enters the drip
lines. A water meter can be placed after the pressure control or
between a solenoid valve and each zone. An air vent provides vacuum
relief. Vacuum relief is necessary between the solenoid valve and the
drip tapes to avoid suction of soil into the emitters when the system
is shut off.
If a drip hose system is used on the soil surface for
over a number of years, the drip hose should be lifted periodically so
leaves, soil, and debris do not cover the hose. If the drip hose is not
lifted, roots can grow over the hose, anchor it to the ground, and
eventually pinch off the flow of water.
Flow of water
Place a water flow meter between the solenoid valve and each zone and
record it's gauge daily. This provides a clear indication of how much
water is applied to each zone. Records of water flow can be used to
detect deviations from the standard flow of the system, which may be
caused by leaks or by clogged lines. The actual amount of water applied
recorded on the meter can be compared with the estimated crop water use
(crop evapotranspiration) to help assure efficient water management..
Watch for Leaks
Leaks can occur unexpectedly as a result of damage by insects,
animals, or farming tools. Systematically monitor the lines for
physical damage. It is important to fix holes as soon as possible to
prevent uneven irrigation.
Chlorine Clears Clogged Emitters
If the rate of water flow progressively declines during the season, the
tubes or tape may be slowly plugging, resulting in severe damage to the
In addition to maintaining the filtering stations, regular flushing of
the drip tube and application of chlorine through the drip tube will
help minimize clogs. Once a month, flush the drip lines by opening the
far ends of a portion of the tubes at a time and allowing the higher
velocity water to rush out the sediment.
Because algae growth and biological activity in the tube or tape are
high during warmer months, chlorine usually is applied at 2-week
intervals during these months.
If drip lines become plugged in spite of maintenance, many cleaning
products are available through irrigation systems suppliers.
product appropriate for the specific source of contamination.
irrigation and fertilization
together to optimize efficiency.
Chemigation through drip systems efficiently delivers chemicals in the
root zone of the receiving plants. Because pf the precision of
application, chemigation can be safer and use less material. Several
commercial fertilizers and pesticides are labeled for delivery by drip
Injection pumps with backflow prevention devices are necessary to
deliver the product through the drip lines. These pumps allow for
suitable delivery rate control, while backflow prevention protects both
equipment and the water supply from contamination. remember that in
Oregon, water belongs to the public, not the landowner. Other safety
equipment may be required; contact a drip-irrigation system supplier
microorganisms convert nitrogen (N) fertilizers to nitrate. Nitrate is
water soluble, available to plants, and subject to leaching loss. Since
nitrate loss management was one of the initial reasons for our
drip irrigation, it is appropriate that we revisit this topic.
Typically, when irrigation is monitored closely,
fertilizer is needed with drip irrigation systems than with furrow
irrigation systems because the fertilizer is spoon-fed to the root
system and little is lost due to leaching. For example, if a field is
converted from furrow irrigation to drip irrigation and the amount of
nitrogen fertilizer is not reduced, the
crop may become excessively leafy which can inhibit curing and increase
harvest costs as well as losses. Leaf tissue analysis performed by a
qualified agricultural lab can help determine crop nutrition needs
during the season, and tailor the N fertilizer applications to actual
Fertilizer can be
injected through the drip system. Fertilizer usually
is introduced into the irrigation system in front of the filter station
so the filters can remove any precipitates that occur in the solution.
Fertilizers containing sulfate, phosphate, calcium, or
anhydrous or aqua ammonium can lead to solid chemical precipitation
inside the drip lines, which can block emitters. Obtain chemical
analysis of your irrigation water and seek competent technical advice
before injecting chemical fertilizers into drip systems.
Placement of Tape
Plan for seed emergence. The drip tape must be close
to the surface to germinate the seed if necessary, or a portable
sprinkler system should be available. For example, a tape tube 4 to 5
inches deep has successfully germinated onion seeds in silt loam
soil. Tape at 12 inches failed to uniformly germinate onions.
Timing and rates
The total irrigation water requirements for crops
grown with a
system is greatly reduced compared to a surface flood system because
be applied much more efficiently with drip irrigation. For example,
with furrow irrigation, typically at least 4 acre-feet/acre/year of
water is applied to onion fields in the Treasure Valley of eastern
Oregon and southwestern Idaho. Depending on the year, summer rainfall,
and the soil, 14 to 32 acre-inches/acre of water has been needed to
raise onions under drip irrigation in the Treasure Valley.
Applying more water than plants need will negate
drip irrigation's benefits. The soil will be excessively wet, promoting
disease, weed growth, and nitrate leaching.
To determine application rates, use measurements of
water and estimates of crop water use (crop evapotranspiration, or
"ETc"). For shallow rooted crops, irrigate only to replace the soil
moisture deficit in the top 12 inches of soil. It usually is not
necessary to exceed ETc. Daily
evapotranspiration estimates are available locally on the AgriMet
Web site. For measuring soil water, see "Instrumentation
for Soil Moisture Monitoring" and "Irrigation
monitoring using soil water tension".
For planning irrigation scheduling, see "Irrigation Scheduling."
Add chlorine or other chemicals to the drip line
periodically to kill bacteria and algae. Acid might also be needed to
dissolve calcium carbonates.
Filters must be managed and changed as
with filtration, however, drip tape must be flushed regularly. The
frequency of flushing depends on the amount and kinds of sedimentation
in the tape.
Root intrusion needs to be controlled for some
Rodents must be controlled, especially where drip tape is buried.
Drip Irrigation for Row Crops. 1994.
and Prichard, University of California, Davis. Order from
Extension office, Department of LAWR, 113 Veihmeyer Hall, University of
California, Davis, CA 95616, telephone (530) 752-1130.
B.C. Trickle Irrigation Manual. 1999. Van
of Agriculture and Food Resource Management Branch. Order from
Association of British Columbia, 2300 Woodstock Drive, Abbotsford,
Canada, V3G 2E5, telephone (604) 859-8222.
Fertigation, 1995, Burt, O'Connor, and
State University. Order from The Irrigation Training and Research
California Polytechnic State University (Cal Poly), San Luis Obispo, CA
93407, telephone (805) 756-2434.
Micro irrigation Management and Maintenance.
A.. Fresno, CA, Agro Industrial Management, 1998. The book is
from Farouk A. Hassan, Ph.D.
Irrigation & Soils Consultant, Agro Industrial Management, P. O.
Box 5632, Fresno, California 93755, U.S.A. Phone:
Fax: (209) 348-0721, E-mail: email@example.com
in Tree and Vine Micro Irrigation Systems.
2001. Schwankl, L. and T. Prichard. Agriculture and
Natural Resources Publication 21599. University of California, Davis,
Resources on the Web:
2003. Avoid Filter Frustration. Available online at
Shock, C.C., R.J.
Eldredge, A.P. Pereira, and L.B. Jensen.
irrigation guide for potatoes in the Treasure Valley. Oregon State
University Extension Service. EM 8912 8p.
Shock, C.C., R.J. Flock, E.P. Eldredge, A.B. Pereira, L.B. Jensen.
Potato Irrigation Scheduling. Oregon State University
Extension Service, Corvallis. EM 8911-E. 8p.
Shock, C.C., R.J. Flock, E.B.G.
Feibert, A.B. Pereira, and M. O’Neill.
irrigation guide for growers of hybrid poplar. Oregon State
University Extension Service. EM 8902 6p.
Shock, C.C., R.J.
Feibert, C.A. Shock, A.B. Pereira, and
L.B. Jensen. 2005. Irrigation
monitoring using soil water tension.
Oregon State University Extension Service. EM 8900 6p.
forum with search features with discussions of all sorts of problems.
Irrigation - Information Site.
Prepared by Clinton C. Shock,
Superintendent, Malheur Experiment Station, Oregon State University.
June 2001., updated August, 2006.
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