Pesticide and Environmental Update
Peppers’ Water Needs:
Middle East Meets American West
In the San Joaquin Valley of California, visiting soil scientist Ron
Seligman collects data underground inside a lysimeter while visiting
engineer Nedal Katbeh-Bader (left) and visiting soil and water scientist
Naem Mazahrih place equipment to compare accuracy of soil-water sensors.
Crisp, crunchy bell peppers in a rainbow of bright colors add texture,
flavor, and pizzaz to new and traditional foods of the Middle East.
An appetizer of yellow bell peppers and sun-dried tomatoes, for
example, is a “must-try” treat in some Middle Eastern restaurants. And
a favorite around the world—shish-kebabs made with slices of red, green,
yellow, and purple bell peppers, skewered between pungent white onion, and
generously sized cubes of fresh lamb or chicken—originated from this
part of our planet.
Fresh vegetables and fruits are a prized and popular part of meals in
the Middle East. And some fresh produce from this sun-drenched region
makes a lucrative export to European markets.
But the competition between Middle East growers and city dwellers for
clean, fresh water is intense in this mostly hot and dry land. The same
scenario is unfolding in many arid regions of the American West.
How Much Water Does a Bell Pepper Need?
The accelerating need for good-quality water has increased the thirst
for knowledge of how to grow premium produce—like delicious bell peppers—with
the least possible amount of water.
Like growers in the Middle East, vegetable producers working 9,000
miles away in California’s famed San Joaquin Valley—one of the world’s
most productive agricultural regions—grow bell peppers in an
Bell peppers, along with broccoli, lettuce, and onions, are relatively
new crops for the west side of the San Joaquin Valley. “There’s very
little information about pepper plants’ water use here on the west side,”
says James E. Ayars, an ARS agricultural engineer. He’s based at ARS’s
San Joaquin Valley Agricultural Sciences Center at Parlier, California.
Applying too little water “can stress the plants, which can lower their
resistance to attack by insects or diseases,” notes soil scientist
Steven R. Evett. Applying too much water is not only wasteful but also “poses
a risk that the excess water will seep into the underground water supply,
perhaps bringing farm chemicals, salts, and toxic elements with it,” he
Evett works in another water-scarce venue—Bushland, in the Texas
Panhandle. “Both the Bushland and Parlier labs neighbor farmlands that
are heavily irrigated,” he notes. ARS research on how to use the water
more efficiently is, he says, vital to the future success of farms and
orchards faced with declining water supplies.
Pinpointing peppers’ precise water needs is a focal point of a lively
collaboration between Ayars, Evett, and Middle Eastern scientists Ron
Seligman from Rehovet, Israel; Naem T. A. Mazahrih of Ajloun, Jordan; and
Nedal A.Q. Katbeh-Bader of Hebron in the Palestinian Authority.
Agricultural engineer Thomas J. Trout, now with ARS in Colorado,
participated in the pepper research while based at the Parlier laboratory.
Array of Irrigation Options Explored
The visiting scientists worked with Ayars and Trout to track plants’
water use at sites that had one of three common types of irrigation
systems: furrow, in which water flows down channels between crop rows;
surface drip, in which water is delivered to plants a drop at a time via a
network of flexible black tubing; and subsurface drip, in which the tubing
is buried beneath the surface and the water is delivered directly to plant
roots, where it’s most needed.
Peppers received one of four different amounts of irrigation water from
the furrows or tubes. These amounts ranged from replacing some, all, or
more than all of the water that plants took up from the soil.
Scientists monitored the pepper plants’ water use by measuring the
change in weight of a research lysimeter—a large, in-ground, soil-filled
box with pepper plants growing on top of it and a huge scale beneath it.
The lysimeter data is a first step toward determining what’s known as
a “crop coefficient” specifically for bell peppers. The region’s
farm advisors, irrigation specialists, and growers—who may not have the
benefit of their own research lysimeter—can use the figure to calculate
how much water their pepper crop used in the previous several days.
“From there,” says Evett, “you do some pretty straightforward
adding and subtracting and use your answer to decide how much of that
water you want to replenish, if any, and when you should do that.”
Evett’s Bushland laboratory and Texas A&M University make
crop-water-use information available every day of the year for major crops
grown in the Panhandle. “It’s invaluable for irrigation scheduling,”
Soil Probes Pepper the Parlier Plots
Bell pepper plants were also the crop of choice for an experiment that
pinpointed the accuracy of an array of different soil-moisture sensors.
Scientists, irrigation consultants, and growers lower these devices
through vertical metal or plastic pipes called “access tubes” to get a
real-time, underground reading of the amount of moisture in the soil
profile. It’s one way to determine how much water is available to slake
If probes are “sufficiently accurate and reliable, they could be an
alternative to lysimeters for tracking a crop’s water use,” says Evett.
He designed and led the soil-sensor study, a segment of a 5-year
investigation funded in part by the International Atomic Energy Agency.
The agency promotes peaceful uses of atomic energy. One such use is the
neutron probe, regarded as the gold standard for determining soil
moisture. But the probe requires a license to use, Evett says.
In all, the scientists evaluated the neutron probe and four newer kinds
of sensors at 36 sites throughout the amply-drip-irrigated pepper plots at
The scientists monitored sensor readings for the entire growing season.
The study spotlighted the worrisome variability in water-content estimates
from the newer sensors, which matched results obtained at Bushland. Says
Evett, “We also showed how many sensors of the same type you would need
to get enough readings for a reasonably accurate soil-moisture estimate.”
The numbers were so large that use of the newer sensors proved too costly
for crop water use studies.
A Little History
This collaboration was the brainchild of Ibrahim M. Shaqir, a Middle
East and North Africa specialist with ARS’s Office of International
Research Programs, Beltsville, Maryland, and manager of the project; Dale
A. Bucks, a former ARS national program leader, now retired; and Charles
A. Lawson, of the U.S. Department of State’s Bureau of Near Eastern
Affairs, which is funding much of the work.
Plans call for the venture—begun in 2003—to continue through at
least 2008, as scientists on both continents continue to learn from each
other and apply what they’ve learned to other crops.—By Marcia Wood,
Agricultural Research Service Information Staff.
This research is part of Water Resource Management, an ARS National
Program (#201) described on the World Wide Web at www.nps.ars.usda.gov.
James E. Ayars is with the USDA-ARS San Joaquin Valley Agricultural
Sciences Center, 9611 S. Riverbend Ave., Parlier, CA 93648; phone (559)
596-2875, fax (559) 596-2885.
Steven R. Evett is with the USDA-ARS Conservation and Production
Research Laboratory, P.O. Drawer 10, Bushland, TX 79012; phone (806)
356-5775, fax (806) 356-5750.