LANDSCAPING USES OF CROSS-LINKED POLYACRYLAMIDE
IN THE WESTERN UNITED STATES
Western Polyacrylamide, Inc.
Daniel J. Wofford, Jr.
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This paper presents developments in Xeriscape-related applications for cross-linked polyacrylamide, a water-absorbing polymer with a proven lifespan of six years and the capability of absorbing up to 400 times its weight in deionized water. It focuses on application rates and methods for using cross-linked polyacrylamide in establishing native grass stands, and for turf and trees, both new and established. The information in this paper is based on the experience of Western Polyacrylamide, Inc. (WPI), a Tulsa-area firm dedicated to the research and development of cross-linked polyacrylamide.
Application Rates: The (anionic) cross-linked polyacrylamide does not accumulate and hold salt, however the soluble salts in soil and water inhibit water-holding capacity of cross-linked polyacrylamide and other polymers. This makes precise application rates difficult to determine for various locations. For example, absorption rates vary widely from area to area, and even field to field, depending on the water source and soil salt content. For example, a pound of cross-linked polyacrylamide (hereinafter called "the polymer") will absorb up to 48 gallons of rainwater, 32 gallons of Fresno (Calif.) tapwater (from wells) and 22 gallons of Castle Rock (Colo.) tapwater (also from wells).
Application Techniques: With irrigation it seems to make little difference where within the root system the polymer is located. But for dryland plantings (grass, field crops, etc.), current evidence shows that shallow dispersal (1/4" to 1 1/2" deep) to take advantage of any light showers is preferred. This may not be true in desert-like conditions due to the high evaporation rates, but it does appear correct for dryland areas where light summer showers occur several times a month.
Native Grasses: In April 1988 a pasture owner near Sedalia (Colo.) drilled a 5-acre horse pasture with a per acre rate of 50 lbs. of polymer mixed with 25 lbs. of seed. The result is a beautiful stand of grass (on 6" centers), and it was the only field in Sedalia which remained green all summer. Later 40 acres were planted with a Brillian drill in Colorado Springs using 1020 lbs. of polymer per acre, and portions of these plantings which were then immediately hydrated with an 8,000-gallon water tanker responded with excellent stands.
Native grass plantings are often "hit-or-miss" in Colorado, and this technique appears to give the landscaper much better stands. Those involved with native grass experiments feel the ultimate native grass seeder will lay down rows of seed-containing gel (similar to squeezing out toothpaste), and it appears this can be done with only 5 lbs. or so of pulverized polymer (enough to make 100-150 gallons of slurry) at a retail cost of less than $20/acre.
Recently Dr. Herb Sunderman at the Kansas State Agricultural Research Station at Colby used a squeeze pump to drill annual ryegrass mixed into a gel slurry (1 lb. polymer made 25 gallons of slurry). The planting was a technical success, but the stand was spotty, at least in part due to the fact that the planting was over rough ground. Dr. Sunderman plans to continue this promising research this fall.
Turf: We did 10-12 new lawns last year (1988) in the Denver area at rates varying from 5-30 lbs. polymer per 1000 square feet - all with apparent excellent results in reducing water consumption. Based on this experience with home-owner monitored lawns, it appears that 15 lbs. of polymer per 1000 sq. ft. will store 1/2" of extra water (extending watering intervals approximately two days during .25" daily ET periods) and 30 lbs. will store 1" (extending it by at least four days). One customer ignored the rate advice ("no more than 5 lbs./tilled inch/1000 sq. ft."), and produced a lawn mushy in spots by rototilling 30 lbs./1000 sq. ft, but only 3-4" deep.
In Spring 1989 we did two plots at respective rates of 45 and 50 lbs./1000 sq. ft. but went 10-12" deep to avoid the "soft" lawn effect. (WARNING: Little is known about the higher rates and it is possible that under the right soil and water conditions a soft lawn will result despite the 5 lb/in. rule-of-thumb. Be especially cautious in areas with very sandy soil and/or with low salt content in the soil/water.)
Low-Water or Even No-Water Lawns?: In part spurred by the fact that the Front Range of Colorado has numerous light afternoon summer showers, we are attempting to produce actual very low-water or actual no-water lawns using heavy applications of polymer and low-water-using grasses such as fescue, buffalo, Ephraim crested wheatgrass, etc. A Colorado Springs landscaping firm in April 1989 seeded two lawn areas with a fescue mix, using 30 and 45 lbs. of polymer/1000 sq. ft., respectively, tilled to a depth of 10-12". The goal in this monitored test is to determine how close to a "no-water lawn" we can come.
A 1000-sq. ft. area on a south-facing manmade hill in a local Douglas County (Colo.) park was seeded with a fescue mix, and treated with 50 lbs. of polymer rototilled to a depth of 12". The goal is to determine if park picnic areas and athletic fields can be kept green all summer without any irrigation. More such experimental lawns will be done until this theory is either proven or disproven.
New Turf Tests at Colorado State University: Given the need to know reliable application rates and projected water savings, WPI has given a grant to CSU's turf grass expert, Dr. Tony Koski, for detailed rate studies. These tests were started in May 1989 on seeded plots, and should yield some preliminary data by September 1989. Several smaller related studies are underway at other universities. Some of this research will deal with use of the polymer to open up tightly-compacted soils and to predict the polymer's behavior in sandy soils. Some work with the polymer's relationship to fertilizer, growth-retardants and pesticides is also planned.
Application Equipment: Olathe Manufacturing Company, a niche company with Toro,
is developing a series of three reasonably-priced polymer-injection machines for
established golf courses, parklands and home lawns, plus a 24-lb. compressed-air gun for
tree work. Once these four machines come into common use, the landscape industry will have
the capability to retrofit existing landscapes to provide significant water savings:
A.) Olathe Model 831 Polymer Planter: This $4500, 42"-wide, PTO-powered machine slices into the ground 2 1/2 to 4 1/2" deep, and deposits the polymer via hollow knives at the bottom of grooves. It requires a 25-35 hp tractor (hp depending on depth desired) with a 3-point hitch. Since no one yet knows application rates with this type machine, Olathe has given Kansas State University a $20,000 grant to determine proper rates and projected water savings by circa August 1989. The machine has already been field tested in Texas, Arizona, Colorado, California and Kansas.
B.) Olathe polymer injector for lawns: Currently in the design stage, a walk-behind polymer planting machine for lawns is scheduled to be ready for market circa September or October 1989.
C.) Olathe polymer attachment to Toro Groundsmaster: A 24" attachment to the Toro Groundsmaster is being considered for development by Olathe for use by golf courses and other owners of these versatile Toro machines.
D.) Olathe Model 801 (compressed air-injection tree gun): This versatile 24-1b. $1500 compressed-air, earth-fracturing tree gun will likely have a significant impact on tree treatment and planting vis-a-vis Xeriscape during coming years. The gun (coupled to a large 100-150 psi, 150-200 cfm compressor) digs its own hole up to 4' deep with three high-pressure digger jets aided by three small blades on the probe. After the probe has penetrated to sufficient depth, the directional blast jets are used to fracture an area 2-3' deep and 8-12' in diameter. Each time the blast valve is opened, the ground over the entire fracture zone quickly rises and falls 2-4".
Cross-linked polyacrylamide (or fertilizers, sand, Styrofoam pellets, etc.) can be siphoned into the fractured underground area at the rate of one pound every 20 seconds, and this capability to provide excess water storage capacity in tree root systems offers tremendous potential for the general Xeriscape field.
It appears the Olathe Model 801 polymer injection gun will allow Xeriscapers more flexibility in the range of plant materials used, while still creating low-maintenance, low-water landscapes. Basically. it will allow us to do things we've never done before except with certain types of irrigation systems.
For example, we have already planted 34 seedlings at the Little Sahara Recreation Area (a 6" annual precipitation site in Western Utah) by injecting two pounds of polymer (which provides 50 gallons of extra water storage capability) into each tree planting hole. In addition, we are planning to use the Olathe Model 801 to plant seedlings at two harsh (6" or less annual precipitation) roadside park sites in Utah and Wyoming.
The gun also appears useful in fracturing poorly drained lawn and golf course sites, producing normal drainage. By using a rotary jackhammer to open 24" deep holes, we have used the gun to fracture a shale-outcropping home site to allow drainage for trees, and are planning to aerate an old-style, highly-compacted golf course green as an alternative to rebuilding the green.
Survival Tree Planting by the Colorado State Forest Service: The CSFS is now entering its fifth year of using cross-linked polyacrylamide for survival planting of tree seedlings, and several nearby states in the Midwest and Rocky Mountain regions are adopting similar programs with the polymer. The goal with these plantings is to ensure survival at the lowest cost possible. The procedure consists of dipping the bareroot stock in a slurry made from pulverized cross-linked polyacrylamide, then planting the seedlings with one cup to one pint of hydrated crystals into the backfill.
Given the frequent drought periods in Colorado, the CSFS recommends planting with pre-hydrated material unless the planter has the capability to water each hole sufficiently to achieve hydration of the crystals immediately after planting. Cost generally runs 5-10 cents/seedling for the crystals and less than one cent for bareroot-dipping.
Living Snow Fences: Colorado leads the nation with more than 130 Living Snow Fences already planted, and is serving as a model for other states wishing to adopt similar Living Snow Fence programs. Host of the Living Snow Fences are planted with a tree planter using the polymer application rates above for survival planting. Survival rates are high (90-95% or higher), but we have no comparison tests to show how much of the success can be attributed to the cross-linked polyacrylamide which was first introduced into the Living Snow Fence program at a Fall 1987 planting near Kiowa, Colorado. Complicating this assessment is the fact that DeWitt Weed Barrier, a UV-resistant, woven polypropylene material was introduced about the same time into the Living Snow Fence Program.
Chainsaw-Driven Planting Augers: These lightweight, portable augers appear destined to play an important future role in dryland tree planting, especially when used in conjunction with cross-linked polyacrylamide. For example, the CSFS office at Woodland Park (in the mountains west of Colorado Springs) has two portable augers which have greatly speeded up plantings. In a typical planting, 30 holes 4" in diameter and 2" deep can be drilled in less than 15 minutes. The holes are partially filled with water, and the polymer mixed with the backfill as the seedling is planted. The chainsaw, gearbox and auger cost about $1000, but the units are proving durable.
Assessment: An estimated 500,000-1,000,000 seedlings are planted annually in Colorado alone (both by CSFS and private purchasers of CSFS-grown trees), and most longtime CSFS Foresters are convinced the polymer has significantly improved dryland survival planting. Just how much, no one seems to know. However, a Colorado company recently converted to polymer after achieving only 65% survival for the 8000 seedlings they planted in 1988 without polymer. In contrast, we expect similar dryland plantings with polymer to achieve perhaps 90% survival, and eliminate the need for drip irrigation in many situations.
Tree Planting in the Desert: We have growing evidence that certain types of tree plantings heretofore impossible in the desert without supplemental watering may now be possible with cross-linked polyacrylamide. Several tests underway already show promise:
A.) Central Arizona Project: While the official survival count has not been made, a May 1989 walk-through of an Arizona desert site with 125 seedlings planted 1 December 1988 showed a survival rate of about 85% despite one of the driest winters in Arizona history. The following were planted with 0, 1, 4, 8, 12 and 16 oz. of dry polymer hydrated onsite in holes planted primarily with a tractor-mounted posthole digger: Palo Verde, whitethorn acacia, false mesquite, and two species of mesquite-all native to the area.
B.) Little Sahara Recreation Area (NW of Delta, Utah): On 6 and 7 April 1989 a combined
U.S. Bureau of Land Management (BLM) and WPI team planted 268 seedlings at a 6"
annual precipitation desert site. Rates varied from 1/4 oz. to 4 lbs of polymer, with
onsite watering providing one quart to 125 gallons
of water storage/seedling at time of planting. After two months with little natural precipitation, a field inspection showed "more than 85% survival". A wide variety of planting techniques were used, but what makes this test more significant than the Arizona project is that many of the species planted are found in areas with 7"-13" annual precipitation, not normally growing at 6" rainfall sites. Due to time constraints, no controls were planted without polymer, but as a BLM officer clearly pointed out, "We've been attempting to plant trees without follow-up watering for decades at such sites. Just look at the surrounding desert; that is our control."
The "Capping" Theory: One effect of cross-linked polyacrylamide which will have significant impact on landscape applications was first theorized by California tomato farmers (who've realized up to 30% yield increases in canner tomatoes using the polymer). They believe one of the polymer's most important functions in crops may be stress reduction and not simply increased water-holding capacity. They also suggest that distribution of the crystals uniformly in the 4" deep tomato beds may help retard the normal upward capillary action which causes soil moisture loss through evaporation.
To test this theory at the Little Sahara Rec. Area (Utah) we rototilled 50 lbs. of polymer into a 1000 sq. ft. area, raked in one lb. of Ponderosa pine seed (for a Forest Service test), and soaked the area to hydrate the polymer. We plan to dig test holes periodically both under the bed and in the nearby desert (which initially had moisture down 2 1/2' from spring snows). Test holes done in late May 1989 showed significantly less drying under the bed, though this may have been due to our watering. Further research is needed to examine this "capping" theory, in part for the potential impact it may have on turf grass management.
Summary: Considerable interest has been generated in adapting cross-linked polyacrylamide to a wide variety of landscape (and agricultural) applications. Its early promise appears to be borne out by the preliminary results seen so far. Both formal and informal research indicates that the polymer will have considerable impact in reducing watering requirements for plants when applied at the proper rates. WPI continues to sponsor research into both application rates and the machines with which to apply the polymer. All current focus is on cross-linked polyacrylamide due to its long life.
For future research, we are searching for a naturally occurring systemic game-repellent which could be hydrated with the polymer and placed in the planting holes of small trees. The idea is to turn the taste of the tree off to repel various animals.
Another promising project already begun on a limited basis is to mix the polymer in the soil mix for seedling trees. Based on transplant work being done with vegetables we believe that the crystals attached to the root systems of small seedlings will someday significantly improve bareroot plantings.
This modern cross-linked polyacrylamide was developed in 1982 but gained little popularity during its first five years due to high prices, and lack of research. However, the combination of retail prices dropping below $5/1b. (in 50-# bags) plus extensive research programs (WPI alone has research projects at 24 universities, primarily in agriculture) has apparently generated the momentum needed to make this fine product practical and affordable for a wide range of uses. The development of a line of polymer-injecting equipment by Olathe and others is expected to further popularize the use of cross-linked polyacrylamide.
NOTE: This abstract is based on a talk presented to the Central California Xeriscape Conference on 4 May 1989. For additional details on the Olathe Equipment, please contact Olathe Manufacturing Company, 100 Industrial Park, Industrial Airport, KS 66031, telephone: 1-800-255-6438 or 1-913-782-4396.
Copyright 1989 by Daniel J. Wofford, Jr, and Dale Greenwood.