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A Polymer for the Drought Years
by Daniel J. Wofford Jr.
and Anthony J. Koski, Ph.D.
Colorado Green · Summer 1990
Cross-linked polyacrylamide may help keep Colorado
green into the 21st century, while significantly
reducing landscape water usage
The almond tree above was transplanted near Bakersfield,
California, as a 2-foot sprig 10 months previous to this photo
with 6 ounces of polymer in the planting hole root zone.
The almond below received no polymer treatment. (photos
by Daniel J. Wofford, Jr.)
In April of 1988, Gary and Pam Pippin, residents of
water-restricted Castle Rock, Colorado, installed 1,000 square
feet of bluegrass sod in their front yard. For two years,
they've given their lawn up to a third less water than the
neighbors, and have even left it unwatered several times
during summer vacations. Yet, today their lawn is the
greenest, most attractive lawn in the neighborhood. And, they
estimate their water savings to be 30 percent or more.
What's their secret? Before the Pippins laid their sod,
they rototilled into the soil 20 pounds of cross-linked
polyacrylamide, a synthetic polymer capable of absorbing up to
400 times its weight in deionized (pure) water. Other
homeowners along Colorado's front range have reported similar
success, using polymer rates in the range of 15 to 30 pounds
per 1,000 square feet of soil.
While more scientific and definitive evidence is being
pursued in studies at Colorado State University, the
satisfaction of homeowners who see green lawns and water
savings is undeniable.
Cross-linked polyacrylamide is a rock-salt-sized granular
material which soaks up free water in the soil, swelling to
1/4- to 1/2-inch in diameter and storing the water for the
plant's use. Plant roots grow through the gel-like particles
and draw out water as needed. A finer powdery grind
used primarily as bareroot dip and the standard crystals are
the two grind sizes emerging as the most useful.
Roughly 95% or more of the absorbed water is available to the
plant.
Cross-linked polyacrylamide was developed in the 1950s by
an American company, but would only absorb 20 times its weight
in deionized water. The patent expired in the 1970s, and a
British firm brought the absorption rate up to 40 in 1978,
then to 400 times its weight in 1982. However, the product did
not take off in the marketplace as expected, due to a
combination of lack of adequate distribution system,
artificially high prices and absence of a concentrated
research effort. Basically, no manufacturer would devote
sufficient development money to a product for which the patent
had expired.
Several companies market the modern 400X cross-linked
polyacrylamide under brand names such as Hydrosource,
Terra-Sorb, Water Grabber, and Broadleaf P4. Competition has
brought the price down to a level affordable for a wide
variety of landscaping uses.
Because of its general high performance, unusual longevity
and safety, cross-linked polyacrylamide is emerging as
the Rolls Royce of the water-absorbing polymers. The longevity
makes it especially appealing for landscaping use, and
original 1982 test plots in the United Kingdom reveal the
polymer still appears to be more than 90% effective after
eight years.
For Colorado landscapers, the most promising uses for
cross-linked polyacrylamide include reduction of turf watering
costs, inexpensively increasing survival rates for
transplanted trees and shrubs, increasing the growth rate of
landscaped plants for earlier maturity, decreasing bedding
plant losses, and improving native grass stand establishment.
Reducing watering costs on sod
It is estimated that 15 pounds of cross-linked
polyacrylamide per 1,000 square feet will technically store
one-half inch of typical Front Range irrigation water, and 30
pounds will store one inch of water. If these technical
storage figures are correct in actual soil conditions,
we should be able to extend watering intervals by two and four
days, respectively, with the 15 and 30 pounds per 1,000 rates
under typical August evapotranspiration rates of one quarter
inch.
This is being seen in many of the 70 to 75
homeowner-monitored polymer lawns with which Western
Polyacrylamide, Inc., (WPI), a Colorado-based polymer company,
has assisted; but we are awaiting the results of Dr. Anthony
Koski's Colorado State University (CSU) turf test for
documented confirmation. (The results are due in summer of
1990). This polymer turf test, considered one of the most
comprehensive in the United States, contains rates from 0 to
80 pounds per 1,000 square feet, depths from 1 to 8 inches,
and has both fescue and bluegrass sections with Hydrosource®,
along with side-by-side comparisons of seven other polymers
and grind sizes. Dr. Koski also is conducting a separate
polymer-sod study supported by the American Sod Producers
Association.
Eleven month old smooth brome grass plant which invaded
polymer in Russian olive planting hole shows benefit of
water-absorbing treatment. (photo by DanieI J. Wofford, Jr.)
In April 1990, the Department of Public Works of the City
of Arvada (Colorado), Green King Landscape and Maintenance
Company, and WPI cooperated to create a polymer test lawn at a
model home site, with a control lawn next door. The test lawn
received 30 pounds of polymer per 1,000 square feet. The
Department of Public Works provided the individual water
meters, and will assist in monitoring the test.
The many variables in water and soil conditions will make
determining application rates for turf an inexact science, but
the CSU tests will provide an excellent baseline study.
For new lawns, the polymer is easily applied with either a
walk-behind or handheld whirlybird spreader. Spreading must
be done evenly, or the results will show unevenness during
periods of stress.
We are already seeing a tendency on the part of some
landscapers and homeowners alike to cut back on the higher
rates (15-30 pounds per 1,000 square feet) in favor of less
expensive rates in the range of 315 pounds per 1,000 square
feet. Landscaper profits are cut, the homeowner will not be as
satisfied in the long run, and the reputation of the
polymer is damaged. Some type of written standards will be
needed to assist customers in choosing their options.
0lathe Model 831 polymer planter drilling polymer 4
inches deep during February 1990 athletic field trials at
California State University/Bakersfield. The company plans to
develop a smaller, walk-behind polymer planter for the home
lawn market. (photo by DanieI J. Wofford. Jr.)
Year old tall fescue sod grown at very high rate of 80
pounds polymer per 1,000 square feet in Colorado State
University's cross-linked polyacrylamide field trials. (photo
by Dr. Anthony Koski)
Golf course and home lawn polymer injection machines
For installing polymer under existing turf, Olathe
Manufacturing, Inc., has developed a polymer-injection
machine, the Olathe Model 831 Polymer Planter, for use on golf
courses, parklands and sports fields. Pulled by a 40hp or
above tractor, the Model 831's PTO-powered blades slice into
the ground at depths of 2-1/2 to 4-1/2 inches on 6-inch
centers to deposit the polymer crystals.
In 1989, Olathe gave Dr. Jeff Nus of Kansas State
University a $20,000 grant for a major polymer rate study of
this type of injection, and this research is continuing - as
is a companion study using polymer to develop a new, "softer"
athletic field to reduce injuries to athletes and a third
study to determine rototilled rates. Some Denver-area tests of
the new Model 831 were planned for late May or early June
1990.
Olathe also plans to develop a smaller walk-behind "polymer
planter" for the home lawn market, and has targeted the fall
of 1990 to put the machine on the market.
Survival Plantings
The Colorado Forest Service is now entering its sixth year
of using cross-linked polyacrylamide for increasing survival
in its seedling and living snow fence programs, with a
technique that includes bareroot-dipping bareroot seedlings
with a slurry solution of pulverized (fine) polymer, and
mixing a cup to a pint of hydrated standard crystals in with
the backfill of all bareroot and containerized stock. Polymer
costs for this type of planting are 5 to 10 cents per tree.
More than a million trees are now planted annually in Colorado
using this technique.
Accelerated tree growth
Tests with California almonds (chosen as a fast-growing
tree) show that 6 ounces of polymer incorporated around the
root system in the augured planting hole will give 30 to 40
percent faster growth (with a doubling of the tree's lateral
root system) in the initial four months. The difference
narrows to 15 percent after 10 months as the tree's size
outstrips the usefulness of the six ounces of polymer.
With a large compressed-air injection gun developed by
Pitts Carbonic, tests have been initiated to determine whether
the accelerated growth can be continued into the second, third
and fourth years. By inserting the gun to 1-, 2 and 3-foot
depths, polymer can be injected into 3-, 6- and 9-foot
diameter areas, respectively.
Similar injection work is being done with four other types
of compressed-air injection guns (Grow Gun, Olathe, Aqua-life
and Terralift) and the Olathe series of mudpumps which pump
hydrated polymer.
Bedding plants
The fact that frequent watering by bedding plant retailers
is annoying, often messy, and labor-intensive contributes to
the estimated 15% loss on all bedding plants which die after
leaving the nursery. However, cross-linked polyacrylamide
shows signs of not only reducing the high mortality, but also
in lowering the bedding plant growers' cost both by early
maturity and by cutting labor needed for watering.
For example, Lee Junglen and Ron Smith of Flower Floral,
Fountain, Colorado, in 1989 converted one-half of their
three-acre cold-frame bedding plant operation to cross-linked
polyacrylamide by having one pound of polymer (one-half the
recommended rate) mixed into each cubic yard of soil mix.
Previously dependent on four full-time waterers over the
spring season, Flower Floral reduced watering costs by 50% as
two employees were able to handle the watering chores. By
increasing the rate to two pounds of polymer per cubic yard
for 1990 and converting 100% to polymer, an additional
significant reduction in labor costs has occurred. Junglen
reports that growing with polymer has only pluses, but does
require some adjustments, such as changing planting
dates for tomato bedding plants which mature two weeks earlier
than usual when grown in polymer.
Native grass seeding with polymer
Over 300 acres in Colorado, Wyoming and Utah have been
seeded with 10 to 20 pounds of Hydrosource Standard (crystals)
per acre mixed with the grass seed or drilled separately into
the seed row via insecticide boxes. In most cases, results
have been excellent, and the technique appears promising for
"out of window" plantings.
If the polymer is hydrated (either by watering or rainfall)
as the seeds enter the crucial germination stage, then high
success rates are achieved. This is because even a light rain
will result in the temporary storage of 400 to 800 gallons of
water per acre in the seed rows at the 10 to 20 pounds
per acre polymer rates.
WPI currently is exploring with the USDA Agriculture
Research Service, USDA Soil Conservation Service, and the
Department of Interior's Bureau of Reclamation, among others,
the feasibility of gel-seeding native grass seeds. The
technique involves mixing the seed with a gel made from
pulverized polymer which would be squeezed
"toothpaste-fashion" into the seed row. Gel-seeding native
grass seeds has been accomplished by a number of researchers
during past years, but improved gels, lower costs and
increased need may make gelseeding a reality for the future.
Gel-seeding, an old technique achieved most recently
by Dr. Herb Sunderman of the Kansas State University's Colby
Ag Research Station, with a liquid fertilizer squeeze pump, is
appealing because it deposits the maximum amount of stored
water into the seed row at the minimum price. For example,
using rainwater, five pounds of polymer (fine), at $20.00 or
less, will produce more than 200 gallons of gel.
Additional uses for polymer
Proposed polymer storage beds
The ability of cross-linked polyacrylamide to store large
amounts of water under trees and shrubs opens a whole new
dimension for innovative landscape architects and engineers.
For example, Lakewood, Colorado landscape architect Jan
Caniglia has proposed a system to capture and channel roof
runoff water into large polymer storage beds under plants
scattered around a xeriscaped yard. By funneling the runoff
water from a 2,000 square foot roof into certain growing areas
containing "polymer beds" (which might include porous rock as
well), this system should allow the growing of most any type
of tree or shrub design combination with natural rainfall or
snowmelt only.
In effect, by concentrating the natural precipitation from
the roof it may theoretically be possible to double or triple
the "annual rainfall" available to the much smaller
flower, shrub and tree areas of the yard. With the various
compressed-air devices available for injecting polymer
crystals into the ground up to three feet deep and 15 feet in
diameter, the landscape architect simply has to mark the
design with the diameter, depth of injection, and pounds of
polymer to be stored in each bed. For plants with shallow root
systems, the polymer could be rototilled into the beds.
A one-quarter inch rain on a 2,000 square foot roof would
quickly deliver approximately 310 gallons of water to soak
deep into the polymer storage beds. In contrast, the same
quarter-inch rain over the growing area might only
penetrate an inch or less into the soil. With each
pound of cross-linked polyacrylamide known to store 25 to 40
gallons of rainwater in the soil, the landscape
architect could carefully tailor the storage system to fit the
roof size, area rainfall pattern, and plant requirements.
Raised flower beds
The Parks, Recreation and Libraries department of
Westminster, Colorado, tired of the high cost and complaints
from twice-daily watering of a highly-visible 600 square foot
raised petunia flower bed, recently installed a very high rate
of polymer (70 pounds per 1,000 square feet) in a test to
determine whether they can keep the petunias in bloom with
natural precipitation and/or limited watering only.
From a technical standpoint, 70 pounds per 1,000 square
feet will give a potential storage capability of about 2-1 / 2
inches of water, and the 12-inch depth to which the site was
rototilled will probably not create a mushy flower bed. By
comparing the pounds of polymer to the cubic feet of soil
involved, we note the rate is roughly two pounds per cubic
yard of soil: a rate considered optimum for polymer-loaded
soil mix for flowers.
Loading on polymers
Cross-linked polyacrylamide and other polymers appear
promising as carriers for fertilizer, micronutrients,
pesticides, herbicides, growth retardants, systemic game
repellents, nematocides and fungicides. The biggest news in
the loading field is a February 1990 decision by the TVA's
National Fertilizer and Environmental Research Center (NFERC)
to assign eight to 10 scientists to the loading of fertilizers
and micronutrients onto different polymers.
This new NFERC program represents the first significant
U.S. government research effort into synthetic polymers. A
1989 NFERC preliminary greenhouse study into loading of 32% (UAN)
nitrogen onto cross-linked polyacrylamide resulted in 50%
larger plants and 40% better utilization of nitrogen. NFERC
research is now concentrating on both nitrogen and iron
loading.
Part of the attractiveness of polymer loading is that each
pound of standard crystals contains approximately 67,000 to
70,000 crystals, thus allowing a form of slow release simply
by altering the dispersion pattern. The 67,000 to 70,000
figure is proving useful in other ways. For example, we can
roughly calculate the density of a broadcast application
simply by counting the number of crystals which fall over a
square foot area.
Game repellents
Ani-pel is a systemic, biodegradable game repellent
containing denatonium benzoate (Bitrex), one of the ten most
bitter substances in the world, and the only one which is
water-soluble. In addition to the commonly-used tablet form,
it holds considerable potential for loading on polymer
crystals. The U.S. Forest Service is experimenting with the
raising of seedlings in a nursery bed containing
Ani-pel-loaded crystals. While the pellet offers
two-and-a-half year protection against all above- and
below-ground animal damage, no one yet knows how much
protection will be offered by the polymer loaded with the
bittering compound.
Russian olive seedling removed 11 months after
transplanting. Seedling was planted with 1 ounce of polymer
(approx. 70,000 crystals) in the original 3-gallon hole, so
the pictured polymer represents perhaps 10% of actual crystals
attached to hair root system.
Polymer performance and safety
Cross-linked polyacrylamide performance is affected
temporarily by salts from both irrigation water and the
ground, but performs much better when hydrated by rainwater or
snowmelt. For instance, a pound of polymer will absorb and
hold 48 gallons (100%) in deionized water, 32 gallons (60%) in
water relatively low in salts, and in the 15 to 25 gallon
range (30 to 50%) in water with higher salt content. Polymer
performance factors (PPF) as low as 11 to 23% have been
seen from certain irrigation in the Lubbock, Texas area,
with such low hydration that agricultural usage on such
sites would not be economical. In contrast, tests from dryland
fields in the same area indicate unusually high PPF of 80% or
better.
Informal tests of irrigation water sources along Colorado's
Front Range show relatively consistent performance, and no
serious performance problems have been seen except from a
shallow surface well in the eastern part of Colorado Springs.
Since the Front Range is (sometimes) blessed with monsoon
showers, both xeriscaped and irrigated sites will benefit from
the higher performance from natural precipitation.
Salt content of soil and water represents one of the few
potential threats to cross-linked polyacrylamide's longevity
(UV light will degrade hydrated crystals sitting on the
surface of the ground over several weeks' time, but doesn't
penetrate more than one-half inch into the soil). Higher
concentration of certain water-soluble salts (e.g. magnesium,
calcium) were recently discovered by two University of
California/Davis researchers to inflict a permanent
"strapping" effect on the crystals, reducing their efficiency
to as low as 10%.
However, no confirmation has yet been found of this
"strapping" effect at an actual field site anywhere.
(For instance, the same crystals hydrated from the Lubbock
irrigation well source were flushed with deionized water -
simulating the effect of rain - and then performed at
near normal rates.) It is hoped that the problem remains
confined primarily to high laboratory concentrations of the
various water-soluble salts, although we may face it in
selected nursery situations. Cross-linked polyacrylamide
researchers and companies involved are now paying much more
attention to water quality.
Long-term cross-linked polyacrylamide safety is naturally
an important consumer question given high environmental
awareness levels, but little has surfaced during the 30-plus
years since the original development of the polymer which
would give any special cause for environmental concern. There
is a considerable body of information on polymer decomposition
routes which show that this type of polymer eventually
degrades to produce CO2, H2O and NH4. Current marketplace
activity is causing intensification of polymer research,
including tests to re-verify the non-hazardous nature of the
polymer.
The speed of development of the cross-linked polyacrylamide
industry in landscaping and agriculture appears to be in
direct relationship to the amount of time, effort and money
devoted to research. Given the complexity of the polymer
vis a vis application rates and methods, it is
imperative that it be developed jointly by university
researchers, research-oriented polymer companies and
professional landscapers.
Dr. Anthony J. Koski is the turfgrass specialist for
Colorado State University's Cooperative Extension Service.
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