Aqua Sorb - Soil Moist Polymer for Soil Hydration and Retention
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. The 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.
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, 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.
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.
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.
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.
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.
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 animportant 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 visapplication rates and methods, it is imperative that it be developed jointly by university researchers, research-oriented polymer companies and professional landscapers.