|PHOTO BY JACK DYKINGA, USDA.
|Linear irrigation systems such as this one are especially useful on vegetable crops
on rectangular fields up to 1.5 miles long.
There are two components
to irrigation efficiency, says Dr. David Zoldoske, director of the Center
for Irrigation Technology (CIT) in Fresno, Calif.: uniformity and
timing/amount of water. Manufacturers are improving both, from drip lines
that resist clogging to a software program that text messages growers when
the system has a problem to a soil moisture sensor that’s been to
Drip irrigation is ideal for irrigating hedgerows and
high-cash-value row crops, such as tomatoes, peppers and strawberries.
“Farmers are requesting very low flow emitters
spaced 4 to 6 inches apart on drip tape,” says Zoldoske.
“Permanently installed buried drip is probably preferred [in
California], except along the coast, where strawberry and other small
growers rent or lease land and have to remove it. The tomato processing
industry is adopting SDI [subsurface drip] almost across the board. They
don’t want tomatoes sitting on wet ground.”
Because water is applied slowly and evenly in a narrow
strip near the plant, drip irrigation can better target applied water and
use less energy than traditional sprinklers. There’s potentially less
plant stress, less water wasted due to evaporation and less runoff and
erosion, and therefore less leaching of nutrients into the water supply.
There can also be fewer weeds.
Water doesn’t touch leaf surfaces or
oversaturate the soil surface, so diseases are less of a problem and salts
can be more easily managed in the soil. Fertilizer and chemicals can be
applied efficiently because they are delivered directly to the plant roots.
More field operations can continue during irrigation, especially with SDI.
It can be used in windy and freezing weather, but not for cooling or frost
“Drip irrigation needs to be properly
designed,” Zoldoske says. “Few farmers design their own
equipment for installation. It’s usually better to purchase a tool
that is commercially built.” Subsurface drip irrigation systems
should be professionally designed and can cost $1,500 per acre or more,
depending on the system. GPS should be used to install the pipes and tubing
Surface drip tape can be removed and reused, but care
must be taken to not damage the product during the process. Specialized
equipment, much of it made by Andros Engineering in Paso Robles, Calif.,
installs it, retrieves it and rewinds it into compact rolls to be
Both aboveground and belowground drip are easily
automated. They also can be used with tensiometers such as Irrometer by
Irrometer Company in Riverside, Calif., and electrical resistance blocks
and meters. These measure soil moisture in the rootzone and allow growers
to apply water only when and where it’s needed. PureSense, in
Oakland, Calif., manufactures Irrigation Manager, which monitors growing
conditions both aboveground and belowground.
|PHOTO BY PETE MORTIMER, USDA.
|Soil has been cut away to expose the subsurface drip irrigation (SDI) system in a tomato field.
|PHOTO BY FLOYD ADAMSEN, USDA.
|Surface drip irrigation on a romaine lettuce
field. Fertilizers are injected at various points in
the pipe and mixed with irrigation water at the
Decagon Devices in Pullman, Wash., manufactures a
sensor that is part of the robotic arm on the landing craft
“Phoenix,” which found traces of ice on Mars. Netafim USA,
based in Israel, will be incorporating the sensor in its IrriWise soil
moisture monitoring system.
Although drip irrigation has fewer mechanized parts
than other systems, and leaks are less of a problem due to low flow rates,
problems are harder to find, especially with SDI, which is also especially
hard to repair.
Even clean water can contain enough soil particles and
minerals to clog the openings in the tubing. Depending on the quality of
the water, they can be managed with filters, periodic flushing and
injections of chlorine and acid solutions. Drip systems have been
susceptible to damage by animals, especially rodents, but it is less of a
problem with tubing made of stronger polymers.
SDI is also susceptible to root intrusion and the
backflow of dirt into the drip line when the system shuts off. Netafim is
one of many companies with drip lines that resist clogging, maintain
uniform flow rates at different inlet working pressures and have an
anti-siphon system to prevent dirt backflow.
Sprinklers are designed so the water flow rates, which
are controlled by the operating pressure and the size and shape of the
nozzle, suit the type of soil and the slope of the field.
Micro-sprinklers are best suited for widely spaced
plants, such as those in orchards and vineyards. Emitters are connected to
lateral pipes that usually use tubing .25 to 1/8 inch in diameter and are
mounted on a support stake or connected to supply pipe, according to the
North Dakota State University Extension Service Web site. They throw water
into the air 3 to 20 feet in diameter, usually in predetermined patterns.
Rain Bird in Azusa, Calif., has a micro-quick spray, for example, that
includes “star bird” and “proportional butterfly,”
as well as “fan spray” patterns.
Micro-sprinklers use less energy and water than
traditional sprinklers. They leave larger dry areas, create fewer weed
problems and make it easier to work in the field during irrigation. Flow
rates vary from 3 to 30 GPH (gallons per hour), according to the
university’s Web site. In sandy soils, emitters should be placed
closer to the plants and the flow rate set higher than in less porous loam
or clay. In clay soils, the least porous, the flow rate should be the
lowest, to avoid evaporation and standing water on flat land and runoff on
Micro-sprinklers can be automated and used for
fertigation. They can be used for frost protection, but not in windy
conditions. They’re less prone to clogging, and it’s easier to
Manufacturers make deflectors to prevent water from
spraying into unwanted areas as well as devices to prevent branches and
foliage from distorting the spray patterns. Distortion usually isn’t
a serious problem, though, Zoldoske says, as long as each tree gets the
same amount of water.
“Trees are pretty adaptive,” he says.
“Their roots will go where the water
Sprinkler heads can be mounted on risers above the
canopy to avoid distortion. Shaping vanes, or spokes, create streams of
water that are less susceptible to distortion, but on sandy soils this can
result in unwatered areas. Sprinklers with
spinners offer more uniform coverage.
Rain Bird has a software program, Uniformity Pro, that
helps growers pick the best nozzle and deflector combination for their
The Irrigation Technology Center’s software
program, SPACE (Sprinkler Profile and Coverage Evaluation), allows
designers and growers to place sprinkler heads in almost any configuration
and combination, calculate the uniformity and display the results using
sprinkler test data.
“It’s a visual way to show how water is
distributed with their products,” Zoldoske says.
Center pivot and linear irrigation
“You’ll see more center pivots than ever
before,” he predicts. First, he says, they work, and not irrigating
the corners of fields is less important because of water supply issues,
they can require less labor to operate than other irrigation systems.
With center pivot systems, one long arm rotates around
a central pivot point, usually propelled by electric power. The amount of
water being applied determines the amount of time it takes for one
rotation. Although the outer end of the arm covers a larger area than the
end closest to the pivot, with proper design and installation these systems
deliver a constant flow of water to all cropping areas. They’re best
suited to porous soils, and are easily adapted to slopes that may need
pressure regulators to stabilize the flow rate. They also can deliver
They’re most efficient on round fields, although
most systems have end guns or part-circle attachments that spray into
corners and irregular areas. FieldPLUS, from Lindsay Corp. in Omaha, Neb.,
has a pivoting joint that can be placed at nearly any pivot tower, and acts
as a new pivot point. This allows the outer spans to wrap another 165
degrees in either direction. If it reaches a barrier, the tower
Linear irrigation systems are similar to center pivot
systems, but the towers move in a line, at the same speed and in the same
direction. They’re usually powered by a diesel motor with a generator
on the main drive tower. They’re especially useful on vegetable crops
on rectangular fields up to 1.5 miles long.
|PHOTO BY DOUG WILSON, USDA.
|With GPS and an Internet connection,
irrigation systems such as this center pivot
system can be controlled by remote.
Valley Irrigation, in Valley, Neb., manufactures the
AutoPilot, the first computerized control panel with the ability to perform
GPS calculations for linear irrigation. With the AutoPilot, growers can
automate functions such as changing direction, stopping the machine and
starting and stopping chemigation. The AutoPilot won the Irrigation
Association’s New Product Contest in 2008.
The original, high-pressure sprinklers require more
energy than other center pivot systems. They irrigate a wider radius and
are effective on relatively uneven and sloping land. Medium, low-pressure
and LEPA (low- energy precision application) sprinklers irrigate smaller
areas, but are more efficient in terms of application uniformity, energy
use and water loss through runoff, evaporation and wind drift. Medium and
low-pressure sprinklers perform best on relatively flat land smaller than
LEPA systems use attachments, usually drop tubes,
hanging a few feet above the ground to apply water directly, usually to
alternate furrows. Most often, crops are planted in circular rows, with
furrow diking to contain the water. LEPA systems minimize leaf wetting, are
the most energy efficient, have the lowest evaporation rates and are the
least affected by wind drift of these four systems. Because a relatively
large amount of water is applied to relatively small surface areas,
slopes should be less than 1 percent on most of the field and the
land should be level. GPS can be used for land leveling.
These systems need to be monitored. A software
monitoring program, FieldNET by Lindsay, was the top new agricultural
product at the 2007 International Irrigation Show. It also won the 2007
AE50 Award from the American Society of Agricultural and Biological
Engineers (ASABE). With FieldNET, growers can check the location, status
and water usage of their system, view the pivot positions and make changes
from any Internet connection or cell phone. They can also receive real-time
text messages if there’s a problem. The program also keeps track of
the system’s water usage.
“We have the technology to manage our water
resources in agriculture,” Zoldoske says. “The bigger question
in the future will be dependable supplies and water quality.”
The author is a freelance writer based in Altadena,
Calif. Visit www.FarmingForumSite.com to discuss this article!