USING POLYMERS TO ENHANCE
SHRUB TRANSPLANT SURVIVAL
AND SEED GERMINATION FOR
REVEGETATION OF DESERT LANDS
Garn A. Wallace
Arthur Wallace
areas, especially where the annual precipitation is erratic
in amount and timing, both germination and survival are
problems. To achieve required revegetation under such
conditions it is often necessary to transplant. Transplanting is not always successful, and additional procedures
are needed to increase success.
Irrigation can increase the chances for success of seeding, but in wildland arid areas it is not usually convenient. The amount of water needed is higher than can
easily be applied by tank or by hand. The use of watersoluble polymers to improve water relations and soil
structure in desert soils was discussed at the last shrub
symposium (Wallace and Wallace 1989).
ABSTRACT
Polymer soil conditioners can be useful for several different purposes in the management of arid lands. Among
these is the very inexpensive procedure of applying watersoluble polymers in solution into transplant holes when
trees and shrubs are transplanted. The procedure allows
for the addition of water without destroying any soil structure. Some gypsum is used with the polymer. Good soil
aeration results, and there is no soil interface problem.
Another use is a combination of water-soluble and gel
polymers, which are predissolved and swollen so that some
of the slurry (200 mL to 2,000 mL or more) can be added
to a small depression, seeds are applied on top, and then
the seeds are covered with as much soil as desired. The
polymer mixture supplies water for the germinating seeds
and is well aerated. The water is released slowly, is not
rapidly dissipated into hot, dry soil, and the linear polymer prevents adjacent soil from crusting. The procedure
can enhance seed germination and survival in areas with
very low rainfall.
POLYMERS IN TRANSPLANT HOLES
A solution of water-soluble polymer has been successfully used in the landscape industry to improve transplant survival and subsequent growth of the transplants
(Wallace 1988). The reason for inclusion of solution of
the polymer is to preserve the stability of the soil aggregates, which results in better aeration around the roots
of the transplants. The solution should contain some
gypsum. The soil does not slake and lose its structure
when wet with polymer solution like it will with water
(Wallace and Nelson 1986). The procedure works on sodic
soils, especially if some gypsum is used to provide soluble
calcium (Wallace and others 1986a). The landscape
industry has previously used large amounts of organic
amendments in the soil with transplants to improve
soil aeration (Morgan and others 1986). The procedure
often leads to interface problems in which water will not
easily move across the organic soil-regular soil boundary
(Morgan and others 1986). The use of water-soluble polymer with a very small amount of organic amendment,
if any, gives more satisfactory results and results in no
interface problem (Morgan and others 1986; Wallace and
Nelson 1986).
The concentration in solution of water-soluble polymer
usually used in transplant work with shrubs varies from
200 to 500 ppm. For every liter of polymer solution used
in transplanting a shrub or tree with each 100 ppm of
polymer costs are about 0.1 cent for materials. If 5liters
of 500-ppm solution were used for a single shrub, the cost
would be 2.5 cents. This is relatively small compared
with the total cost of the transplant, which could be $1
or $2.
INTRODUCTION
Environmental regulations currently require that disturbed lands be returned to reasonably close to natural
condition. In areas such as the Nevada Test Site, where
average rainfall is near 100 to 120 mm per year with
a coefficient of variation of around 100 percent, revegetation is difficult. Ifleft alone, the disturbed sites may not
recover for decades (Wallace and others 1980), although
2 successive years of much higher-than-average rainfall
such as experienced at the Nevada Test Site in 1983-85
(Romney and others 1989) will give natural revegetation
with a high incidence ofburrobrush (Hymenoclea salsola),
which has a deep taproot character (Groeneveld and
Manning this proceedings).
Ih ecosystems where rainfall is 300 mm or more per
year, it is usually possible to plant seed in the appropriate
season and expect reasonable emergence. In low-rainfall
Paper presented at the Symposium on Cheatgrass Invasion, Shrub Dieoff, and Other Aspects of Shrub Biology and Management, Las Vegas, NV,
April 5-7, 1989.
Garn A. Wallace is Plant Biochemist and Research Director, L L Company, 1647 Manning Ave., Los Angeles, CA 90024. Arthur Wallace is
Research Plant Physiologist, Laboratory of Biomedical and Environmental
Sciences, University of California at Los Angeles, 900 Veteran Avenue, Los
Angeles, CA 90024-1786, operated for the U.S. Department of Energy by
the University of California under contract No. DE-AC03-76-SF00012.
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The concentration of 500 ppm would be used for clay
soils with less for loam and loamy sand (Wallace and
others 1986b). For soil without structure, such as disturbed subsoil, it is important that aeration be improved
with water-soluble polymers and cultivation where necessary to create aggregates. The polymers used are food
grade (Wallace and others 1986c).
REFERENCES
Azzam, R. A. I. 1985. Tailoring polymeric gels for soil
reclamation and hydroponics. Communications in Soil
Science and Plant Analysis. 16: 1123-1138.
Henderson, J. C.; Hensley, D. L. 1986. Efficacy of a hydrophilic gel as a transplant aid. HortScience. 21: 991-992.
Hunter, R. B.; Wallace, A.; Romney, E. M. 1980. Fencing
enhances shrub survival and growth for Mojave Desert
revegetation. Great Basin Naturalist Memoirs. 4:
212-215.
Morgan, W. C.; Wallace, A.; Wallace, G. A. 1986. Soil
conditions that restrict plant growth. Landscape and
Irrigation. March: 32-36.
Pryor, A. 1988. Pretty poly: Water-absorbing polymers
have been shown to improve yields in processing tomatoes. California Farmer. 269: 12.
Romney, E. M.; Hunter, R. B.; Wallace, A. 1981. Revegetation management and recovery at sites disturbed
for solar thermal power systems development. Report
UCLA 12-1281. 21 p.
Romney, E. M.; Wallace, A.; Hunter, R. B. 1989. Pulse
establishment of woody shrubs on denuded Mojave
Desert land. In: Wallace, Arthur; McArthur, E. Durant;
Haferkamp, Marshall R., compilers. Proceedingssymposium on shrub ecophysiology and biotechnology;
1987 June 30-July 2; Logan, UT. Ogden, UT: U.S.
Department of Agriculture, Forest Service, Intermountain Research Station: 54-57.
Wallace, A. 1987. Anionic polyacrylamide treatment
of soil improves seedling emergence and growth.
HortScience. 22: 951.
Wallace, A. 1988. Daylily success begins with good soil.
Daylily Journal. 43: 258-263.
Wallace, A.; Nelson, S.D. 1986. Soil conditioners. Soil
Science. 141: 311-397.
Wallace, A.; Romney, E. M.; Hunter, R. B. 1980. The
challenge of a desert: revegetation of disturbed desert
lands. Great Basin Naturalist Memoirs. 4: 216-225.
Wallace, A.; Wallace, G. A.; Abou-Zamzam, A.M. 1986a.
Amelioration of sodic soils with polymers. Soil Science.
141: 359-362.
Wallace, A.; Wallace, G. A.; Abou-Zamzam, A.M.; Cha,
Jong Whan. 1986b. Soil tests to determine application
rates for polymeric soil conditioners. Soil Science. 141:
390-394.
Wallace, A.; Wallace, G. A.; Cha, Jong Whan. 1986c.
Mechanisms involved in soil conditioning by polymers.
Soil Science. 141: 381-386.
Wallace, G. A.; Wallace, A. 1989. High-tech polyacrylamides as soil conditioners in the reclamation and
stability of desert lands. In: Wallace, Arthur; McArthur,
E. Durant; Haferkamp, Marshall R., compilers.
Proceedings-symposium on shrub ecophysiology and
biotechnology; 1987 June 30-July 2; Logan, UT. Ogden,
UT: U.S. Department of Agriculture, Forest Service,
Intermountain Research Station: 58-63.
GELS FOR SEED PLANTING
Cross-linked polymers swell in the presence of
water from 50 to 400 times their weight (Azzam 1985;
Henderson and Hensley 1986). Depending on the degree
of cross linking and the base material in the polymers,
as much as 95 percent and as little as 40 percent of the
water in the gels can be available to plant roots. Crosslinked polymers do not combine with clay in soil like the
water-soluble ones do. They contain water that can be
available to plants. Many products are commercially
available, including biodegradeable polymers made from
starch. They have been promoted for many purposes in
agriculture, especially horticulture. Most of these uses
are of minor importance, but one of some interest is that
of drilling from 5 to 50 kg/ha into seed rows of tomatoes
for the purpose of preventing soil crusting, which prevents
or inhibits seed emergence (Pryor 1988). The procedure
does work reasonably well and has been validated by us
with no problem. There is some reported concern that
swelling gels applied to seed rows can fracture roots
of seedlings. We have not seen any indication of this.
Rather than using gels to prevent soil crusting, we
prefer to sprinkle irrigate with water-soluble polymer
(Wallace 1987).
We have done preliminary testing with gel-linear polymer plus gypsum mixtures to promote germination of
seed in dry soil, both in containers and in the field. From
200 mL to 2,000 mL of previously swollen gel with linear
polymer per seed spot has been placed in the soil with
various seed types, then placed on top, and then covered
with a thin layer of soil.
Seeds have readily germinated and emerged. Especially when the gels have been treated to slow their release of water, the gel applications have sustained the
seedlings for 3 or more weeks after seeding into previously dry soil with daytime temperature reaching 38 oc
(100 °F) for several of the days.
In disturbed soils at the Nevada Test Site that have
had no vegetation for a few years, the subsoils contain
adequate soil moisture. to support vegetation, but the
surface soil due to high temperatures is too dry for seed
germination (Romney and others 1981). It is with such
conditions that preswollen polymer mixes can be extremely useful in the establishment of new vegetation.
The seedlings germinating in 2 to 3 weeks would have
time to develop tap roots that are deep enough to penetrate into soil with adequate moisture to promote enough
growth before dormancy in summer. In following seasons
with reasonable rainfall, the new plant can survive, consistent with lack of competition from herbivores. Rabbits
are a regulator of seedling survival at the Nevada Test
Site (Hunter and others 1980).
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