WORLDWIDE RESEARCH SUGGESTIONS FOR CROSS-LINKED
POLYACRYLAMIDE IN AGRICULTURAL RESEARCH

Daniel J. Wofford, Jr.
Western Polyacrylamide, Inc.
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Presented to: The 1992 International Conference for Agricultural Research Administrators – September 13-19, 1992, McLean, Virginia, U.S.A.

Introduction

This paper is a discussion of some of the more promising research options which are emerging in the field of water-absorbing soil polymers. Many include the use of water-harvesting techniques, to maximize cross-linked polyacrylamide’s water-storing capability, and minimize irrigation costs. The paper is based on my extensive work in running a nationwide, research oriented cross-linked polyacrylamide company for over four years. Most of our work has been done in rainfall zones ranging from 10 to 50 cm of rainfall annually. Precipitation patterns vary from summer-long drought to frequent, brief, summer, monsoon-type showers.

Cross-linked polyacrylamide (CLP) is a synthetic water-absorbing polymer made from natural gas, capable of absorbing 400 times its weight in deionized (pure) water, or 150-300 times its weight in irrigation water in most soils. In practical terms this means one kilogram will absorb and store 18 deciliters of rainwater, or 6-12 deciliters (16-30 gallons) under most irrigation circumstances. CLP has an estimated effective lifespan of seven to ten years. Under normal conditions of use it is not adversely damaged by minerals or fertilizers in the soil. However, soluble salts temporarily cut down on hydration capacity of the granules at a predictable rate. We consider cross-linked polyacrylamide to be the “Rolls Royce” of the water-absorbing soil polymers because of high general performance, longevity, and the fact that it is gel-forming.

Cost of Polymer Storage of Water

One kilogram of cross-linked polyacrylamide costs about US$ 6-8 in bulk ($2.75-3.60 per pound). It will not likely prove economical in the majority of conventional farming operations, but a number of intensive small farm/water-capture possibilities are emerging in the Western United States which should be explored worldwide. In addition to some techniques already proving successful in U.S. test plots, we are including some new ideas which we would like to see tested by interested researchers.

AGRICULTURAL/IRRIGATED USES FOR CLP

Intensive Vegetable Raising with High Polymer Rates

This is perhaps the most promising usage for cross-linked polyacrylamide, and U.S. research has barely started in this field. With high rates of CLP (i.e., 3 to 20 kg per 100 square meters – 12 to 45 lbs. per 1,000 square feet), numerous home gardeners across the United States have reported yield increases of 50-200% or even higher for many vegetables (especially tomatoes, sweet corn, etc.). While these tests have not yet been replicated or otherwise documented scientifically, it is obvious that something unusual is happening which causes rapid growth, early maturity and high yields.

We now believe the answer may lie in the fact that the polymer minimizes plant stress by allowing constant uptake of nutrient-loaded water. It appears that even frequent irrigations may not be as effective as the polymer as a mechanism for stress-free even distribution of nutrient-loaded water to the plant. How does this work?

The amount of water-loaded polymer apparently must be sufficient to prevent water stress and allow uninterrupted growth. Insignificant amounts of polymer appear unable to provide necessary water to influence the steady, (relatively) stress-free growth of the plant.

Another key, related explanation may have been discovered by Thomas Hopen, a Lawrenceville, Georgia, microscopist. Hopen’s 32X photomacrograph of a three-week-old tomato root growing through a hydrated granule reveals a proliferation of hair roots growing out from the root – giving the root the appearance of a hairy arm – while the root outside the hydrated granule remains bare and devoid of hair roots.

Photomacrograph of the HydroSource granule showing 3-week-old root growth in the interior of the granule. (Total magnification = 32X)

Vegetable Gardens in Refugee Camps

Any country with refugee camps should experiment with development of a small, standardized refugee garden in which individual refugee families could raise vegetables in the camp on very small plots. This would not only help alleviate costs of imported food for the camps, but would help teach a valuable skill (gardening). For example, each refugee family could be issued seeds, 2 kg of cross-linked polyacrylamide, a water bucket, some fertilizer and a shovel.

(Note: As part of your experiments to develop a “refugee garden,” attempt to grow a number of vegetables [i.e., corn, beans, tomatoes] at extremely high densities. For example, grow sweet corn in a grid pattern 7.5 cm (3 in) apart with a polymer rate of 32-64 kg per 100 sq. m (66-131 lbs./1,000 sq ft). Carefully monitor fertilizer requirements, and keep polymer hydrated. We have some evidence that very high densities of certain vegetables may be grown in this manner.) I have a small (native American) Indian corn (Mandan Bride) test in my personal garden in which I am attempting to raise 60-70 stalks of corn on a plot only 30 cm by 2 meters (1’X6′). Growth as of September 8, 1992 appears identical with the Mandan Bride grown at normal spacing. The corn was planted in late June 1992, but yields appear to be normal for Mandan Bride whether raised with the usual 23-cm (9-in) spacing or at densities exceeding 100 plants per square meter.

Continuem Nutra-Gel (CNG)

A North Logan, Utah, company (Pan-Agro Inc.) headed by a Utah State University professor has developed a patented process for loading cross-linked polyacrylamide with 16-16-16 (or any other combination) fertilizer and micronutrients for a complete growing package. Growth results from the CNG are extremely good, and we are using this fertilizer-loaded polymer as another form of control during tests – -to demonstrate what growth would be if we applied correct amounts fertilizer with ordinary cross-linked polyacrylamide. The current cost of the CNG is almost double ordinary cross-linked polyacrylamide, but it has a promising future – especially in greenhouses, nurseries, gardens etc., because it promotes high growth rates.

During tests, please note that CNG initially hydrates only 30 times its weight in water due to the fact that it is loaded with fertilizers. Slowly the fertilizer is removed from the granules by plant roots, and some leaching occurs, eventually reaching the point where their hydration capacity is equal to that of the original cross-linked polyacrylamide. We suggest researchers experiment with a mixture of CNG (for the fertilizer) and cross-linked polyacrylamide (standard) for vegetable growing. (Contact: Pan-Agro Inc., 2084 North 1200 East, North Logan, Utah 84321, tel: (801)752-5610, FAX: (801)752-5645.)

Vegetable/Polymer Rate Tests

Each type vegetable appears to achieve optimum growth at a specific cross-linked polyacrylamide rate, and we suggest the following rates in a test garden with (for example) eight vegetables:

a.) Control row (no polymer)

b.) 1 kg per 100 sq. m (100 kg per ha) (2 lbs./1,000 sq ft – 89 lbs./ac)

c.) 2 kg per 100 sq. m (200 kg per ha) (4.1 lbs./1,000 sq ft – 178 lbs./ac)

d.) 4 kg per 100 sq. m (400 kg per ha) (8.2 lbs./1,000 sq ft – 356 lbs./ac)

e.) 8 kg per 100 sq. m (800 kg per ha) (16.4 lbs./1,000 sq ft – 712 lbs./ac)

f.) 16 kg per 100 sq. m (1600 kg per ha) (33 lbs./1,000 sq ft – 1424 lbs./ac)

g.) 32 kg per 100 sq. m (3200 kg per ha) (66 lbs./1,000 sq ft – 2848 lbs. /ac)

h.) 64 kg per 100 sq. m (6400 kg per ha) (131 lbs./1,000 sq ft – 5696 lbs./ac)

Incorporate the above rates of polymer in equal rows 20 cm (8 in) deep across the 100 sq. m (1076 sq ft) bed, and plant eight types of vegetable perpendicularly across the bed – through each of the rates. Fertilize normally and water when required (as a peasant farmer might do). Fertilizer requirements will be higher because of larger plants, but high polymer rates significantly lower fertilizer leaching. A tests at Penn State showed that 66% of normal nitrogen was required to raise a tomato crop of equal yield when soil polymers were used.

In addition, at 2 and 8 kg rates per 100 sq. meters (4.1 and 16.4 lbs./1,000 sq ft), also incorporate bars of Continuem Nutra-Gel. At the 4 and 16 kg per 100 sq. meter (8.2 and 33 lbs./1,000 sq ft) levels with HydroSource Standard, add test rows using the seedrow method to help determine where broadcast or seedrow methods are the most effective.

This type test should help establish approximate proper rates for specific vegetables, and allow researchers to better understand the results from both underdosing and overdosing. Ideally, this test bed should be maintained for several years, with different vegetables and flowers grown across the various rates each year. Small fruits and grapes should be grown in permanent plots under similar circumstances.

Frequent Root and Polymer Examination

It is imperative that roots with respect to polymer be examined frequently during the growing season. If necessary, establish some sacrificial plants during each test, examine the roots periodically, and dig up a selective sample at the end of each growing season.

For example, I once pulled up and examined 300 corn roots from a Northrup sweet corn plot which had yielded an average of 3-4 ears per plant. I discovered that stalks with less than 20 granules attached to the roots were much smaller and often had only 1-2 ears per plant. But roots on which I found 20-200 hydrated granules had much thicker stalks with 3-4 ears. This was a seedrow application at about 1.5 kg per 100 sq. m (3.1lbs./1,000 sq ft), and the conclusion I reached was that any number of granules above 20 was enough to make a significant yield and plant size difference under those particular watering conditions at that Colorado garden site.

Early Maturity

Early maturity of 7-21 days is often reported by gardeners and farmers alike using CLP in a wide variety of vegetable crops. This includes 10-14-day early maturity in California field canner tomatoes treated at 20-30 kg per ha (18-27 lbs./ac), 7-10-day early maturity for fall cauliflower at Penn State University treated with 9-18 kg per ha (8-16 lbs./ac), and 14-21-day early maturity with Early Cascade table tomatoes (Massachusetts) grown organically at rates between 400 and 1600 kg per ha (356-1424 lbs. /ac).

For all tests with polymer, please record maturity dates, because it can prove very useful. For example, I would expect that certain vegetables could be grown farther north in Russia due to this shortening of the growing season. In southerly areas with much longer growing seasons, researchers should examine the possibility of squeezing an extra crop into the season (i.e., from 2 crops to 3).

Evaporation Control in Polymer-Loaded Beds

Cross-linked polyacrylamide worked into bare soil often suffers from a natural drying process (loss of performance) in the top 0-8 cm (3.2 in) of the soil profile, and some type of mulch greatly increases performance due to the significant reduction in soil evaporation loss.

The best possible combination is probably DeWitt Sunbelt (polypropylene weed barrier) with at least 5 cm (2 in) or more of bark mulch over the Sunbelt. A 1990 and 1991 test in Wyoming by the USDA Agricultural Research Service, Wyoming State Forestry Division and Laramie County (Wyoming) Conservation District showed that Sunbelt (without polymer) maintained moisture levels at the 85% level or above, while under fallow soil moisture fell to about 3% during the summer and essentially stayed there.

If the DeWitt Sunbelt is unavailable for tests, some type of local bark mulch will accomplish the task in a somewhat acceptable manner. Use of the DeWitt and/or bark mulch will also virtually eliminate the problem of hydrated granules popping out of the top 2-3 cm (0.8-1.2 in) of the soil profile after a hard rain. And both mulching methods dramatically reduce the problem of weeds, including water loss to the weeds.

Garden loaded with 15 kg of HydroSource standard per 100 sq. meters at 35 cm annual rainfall site, and covered with DeWitt Sunbelt (weed barrier). This cut watering cycles from 20-30 per season down to about 10, and also reduced weeding very significantly. With a much higher rate of polymer we can probably eliminate all irrigations. (Littleton, Colorado)

In addition, the high rate of polymer in such a vegetable bed will allow rapid absorption of water from a heavy rain with little water soaking through or running off the surface. For these three reasons, water efficiency is much higher than with conventional gardening systems.

Use of Cross-linked Polyacrylamide in Field Crops

Many of our early experiments with the use of CLP for field crops have been outlined in a November 8, 1989 paper for AgFRESNO titled, “Use of Cross-Linked Polyacrylamide in Agriculture for Increasing Yield or Reducing Irrigation.” Please refer to that paper for field crop test information. The information is somewhat dated (1989), but still considered quite accurate. Results for field crops at low rates (i.e., 40 kg per hectare) have been inconsistent, but with more successes than failures. The best results have been with high-water-using irrigated vegetables such as tomatoes, lettuce, bell peppers and onions. Based on a limited number of tests with San Joaquin Valley (California) farmers, it appears that it may be possible to obtain consistent yield increases of 15-30% with application rates of 25-30 kg per ha (23-27 lbs./ac).

For instance, it appears we can consistently get 20-30% yield increases with canner field tomatoes treated with 20-30 kg per ha (18-27 lbs./ac) broadcast and incorporated into the tomato beds. Most recently a June 1992 article entitled “Pay Dirt” in California Farmer notes that a lettuce grower obtained a yield increase of 15% (973 cartons per 0.4 ha (1.0 ac) for the treated and 845 cartons for the control). This was accomplished with a rate of 30 kg HydroSource Standard per ha (27 lbs./ac) with uniform fertilizer and irrigation cycles. Another California canner tomato test using about 20 kg per ha (18 lbs./ac) (broadcast and incorporated) showed it was possible with polymer to obtain the same yield with 5 irrigations during the season, rather than the normal 7 irrigations.

In 1989 University of California/Davis produced a consistent 7% (4 ton per ha – 9.9 tons per ac) yield increase in replicated tomato trials with low seedrow application rates of 2.3 kg and 22 kg per ha (2-4.5 lbs./ac). The HydroSource Standard was banded with the fertilizer 5 cm (2 in) below the tomato seed, and the researcher credits the fertilizer retention by the relatively light rate of CLP for the yield increase.

Seedrow vs. Broadacre (Incorporated) Applications

Most early CLP successes in the Western United States were achieved by broadcasting and incorporating the polymer to a depth of 10-20 cm (4-8 in), while most failures were with the seedrow method. Yet some universities (notably Pennsylvania State University) have had excellent results with the seedrow technique, and point out that seedrow applications of polymer lessen weed growth between the rows. We have seen few scientific comparisons of the two techniques, and in reality both might have their place under specific circumstances.

For instance, it is possible that cool season vegetables (i.e., cauliflower) with a long taproot and smaller, bunched root system near the surface, might respond better to the seedrow method – whereas tomatoes might perform better with the broadcast/ incorporated method, due to the nature of their extensive root systems. We suggest that each test at lower field crop rates (i.e., less then 50 kg per ha) include both seedrow and broadcast methods until it can be determined which is correct for specific circumstances/crop. (These suggestions deal with field crop applications of CLP, as it is difficult to use the seedrow polymer application method at very high rates [i.e., above 200 kg ha] due to significant swelling of the polymer in the seedrow.)

DRYLAND/WATER HARVESTING TECHNIQUES WITH CLP

Many of the techniques described below are in the most preliminary stages of exploration, yet they all merit consideration. Even if only a few of them prove worthwhile, they could be of great help to people living in arid or semi-arid lands. Ideas for designing catchment systems are included further on.

No-(Irrigation)Water/No-Weed Flowers

In Colorado at 38-cm (15-in) annual rainfall sites, we are currently raising beautiful marigolds (Tagetesspp.) and petunias (Petunia spp.) which do not have to be watered or weeded. This eliminates the normal 25-75 waterings and 8-20 weedings per year. The key to success is that we absorb and store the normal 2.5 to 4.5 cm (1 to 1.75 in) of monsoon-type rains which fall monthly during the hot, Colorado summer.

This photo of the NO-WATER/NO-WEED marigold bed was taken August 5, 1992. (Castle Rock, Colorado)

By covering the bed with DeWitt Sunbelt and pine bark mulch, we control weeds, moisture and erosion. Sawdust could also be used, but we prefer the DeWitt polypropylene weed barriers (which contain an ultraviolet blocker) to achieve our goal of 100% elimination of weeds. This NO-WATER/NO-WEED technology is new and the first 3-4 beds of which we are aware were built by WPI and its customers in Colorado in the spring of 1992.

We do not know if the concept can be used to store water from California’s six-month wet season for use in its dry summer season, but we plan such a trial bed this fall with a University of California/Davis researcher. We know we can store sufficient rainwater for the dry season, but will the various plants be able to survive and thrive in very high polymer-to-soil ratios?

This is the single most important research question with the NO-WATER flower technology yet to be answered. One solution may be to spread extra polymer (i.e., 5 kg per 10 sq. m) on the soil surface after incorporating that much or more into the top 20 cm (8 in) of the bed, and before covering it with DeWitt Sunbelt. This would allow above ground storage of 10 cm (4 in) of extra water which could be tapped into by plant roots running out of the soil into the hydrated surface polymer. Our goal is to trap at least 20 cm (8 in) of water in the bed prior to the onset of summer.

Impermeable Plastic-Covered Vegetable Beds

A word of caution! We are aware of three university tests (cantaloupe, tomatoes, and bell peppers) in which poor results occurred when the impermeable plastic was used to cover a vegetable bed containing cross-linked polyacrylamide. Does the incorporated polymer somehow duplicate some of the functions of the impermeable barrier in retarding the normal, upward capillary action of water with some type of “capping effect?”

This “capping” phenomenon has been verified when higher polymer rates have been used in soil without the impermeable plastic. This assumption that impermeable plastic duplicates the effect of the polymer is based on only three examples, and we do not understand what is happening in these cases. Therefore, we are using this occasion to alert researchers to this potential problem, and would like any information on the subject.

Dryland Berry Farm

In April of 1992 in Colorado we constructed a dryland raspberry (250 plants), blueberry (50) and blackberry (10) farm in a 2286-meter (7500-ft) elevation, 33-cm (13 in) annual precipitation site. We started by building 213 meters (700 ft) of large polymer-loaded contours (1.5 m – 4.5 ft wide) staggered 4.5 meters (15 ft) apart alongside an 8% slope on a south-facing hill. The soil around each plant was loaded with 0.2 kg to 2 kg (0.4-4.4 lbs.) of (dry) cross-linked polyacrylamide worked into the soil 30 cm (12 in) deep, thus giving each plant a water storage capacity ranging from 57 liters to 454 liters.

Initial construction of the dryland, polymer-loaded raspberry contour beds. April 6, 1992. (Peyton, Colorado)

Same dryland raspberry beds as of September 8, 1992. Controls (not pictured) were only 10-15 cm tall due to lack of moisture. (Note cover crop of beans between first and second rows).

The raspberry row in the background was treated with HydroSource cross-linked polyacrylamide, but not mulched. The larger growth of the mulched row in the foreground clearly illustrates the advantages of mulching. (Peyton, Colorado)

Despite the fact that the contours were constructed on April 7, 1992, thus denying us the opportunity to fully charge the storage polymer with winter snowmelt and early spring rains, the 300-plus plants have grown well without any supplemental irrigation water. We predict this water-collection and storage system will allow us to successfully raise small berries (raspberries, blueberries and blackberries) as dryland crops without any irrigation at sites receiving as little as 30 cm of annual rainfall. Not only does the system collect and store most of the rainfall at the site, but we may be able to double or even triple the amount with careful water harvesting in the contours.

Part of the contours are covered with DeWitt Sunbelt (retail cost U.S.$ 1.00 per square meter – yard) and other portions with (free) sawdust. These two types of mulch help control weeds, moisture and erosion.

Will this system prove economical for a Colorado dryland grower? The answer is probably “YES,” as (for example) the typical wholesale price of blueberries is more than US$ 2 per kg ($0.90/ lbs.). Bed construction per plant cost is US$ 12 for the 2 kg of cross-linked polyacrylamide and US$ 0.40 purchase price for each plant – with spare-time labor of the owner to construct the bed. Normal annual yield of a mature blueberry plant is approximately 6-8 kg (13-17 lbs.), which can be sold for US$ 15-20 wholesale or nearly double that price, retail. The HydroSource cross-linked polyacrylamide should remain effective for 7-10 years, so the wholesale profit for only one year may pay for the CLP. (The $12 cost mentioned does not include the fertilizer, insect control, harvesting, marketing, etc.)

(Note: As of September 8, 1992, the polymer-treated raspberry bushes averaged 1.2 meters high and were loaded with fruit, while the control bushes were barely above the 10-15-cm height they had been at planting.)

Dryland Orchards in Arroyos in Semi-Arid Regions

Traveling through northern Mexico’s Nuevo Leon State, I was struck by the number of young dryland apple orchards which produced only 0.4 to 1.6 hectoliters (1-4 bushels) of apples per tree per year while nearby irrigated trees were producing 8-16 hectoliters (20-40 bushels) per tree. Most of the 25-40 cm (10-16 in) annual precipitation falls in a 6-7-month period (winter to spring) during which runoff water occasionally flows down the arroyo. This opens the possibility of building stone catchments loaded with polymer/soil mix.

I do not know of anyone who has constructed polymer-loaded systems for fruit, nuts, or grapes, much less studied the economics of these techniques. However, it is technically possible to make such systems work, and they should be tested with high value fruit/nut trees and grapevines. Each country and each area has high value fruits and nuts which might prove economical to produce with polymer-loaded rainfall-capture systems. The following sketches show three methods of rainfall/runoff capture for growing fruits, nuts and grapes:

Polymer-loaded, rock dam revetments for growing fruit trees in a small, normally dry stream bed which contains water from rains several times a year.

Fruit or nut trees grown in small, polymer-loaded, crescent-shaped stone revetments with V-shaped furrows to channel occasional runoff from rains into the tree root area for storage.

Rock dike catchment system with polymer-loaded soil for growing dryland grapes. In higher rainfall areas, these dikes could be staggered down a sloping hill.

Auguring To Inject Polymer for Fruit Tree Tests

Most of our handful of polymer-injection tests into grape vineyards, orchards, and parklands have been with compressed-air guns, but we have heard of several farmers who have augered 5-8 holes one meter (3 ft) deep and 1.5 cm (4 in) wide around a tree, and filled the hole with hydrated CLP. Then a small catchment basin is built to direct runoff water from small rains into these “wells of water.” Since this technology is easy to implement, researchers should try it for fruit trees, cutting off all water both to controls and treated trees to determine how long fruit trees can survive and produce fruit into the dry season.

These chainsaw augers cost about $US 1000, but one person can auger more than 150 holes per hour.

This crude system might allow economical fruit or nut production in marginal areas where fruit is expensive. The tree roots will soon permeate the wells of stored water in the augered holes. The polymer will not localize root growth, but the tree appears to use the water available to develop a larger root system both in the polymer and outside it.

Designing Rainfall Catchment Systems with Cross-linked Polyacrylamide

In order to design a rainfall catchment system with CLP it is imperative that one study monthly rainfall charts for the area in which the system is being designed. Then, during various rainstorms, walk through the area to study runoff and how it can be captured in small polymer storage beds and utilized later during dry spells for plants. Many of these systems will not be economical except for the highest value vegetables and fruits, but such small, high-yield garden plots should be researched to determine feasibility. In addition, rainfall capture systems also promote erosion control.

Water-Holding Capacity of Various Soils

With cross-linked polyacrylamide at high rates, we can dramatically increase the water-holding capacity of all types of soils. For instance, with the NO-(IRRIGATION)WATER/NO-WEED flowers we are growing in Colorado, we can physically store more than 10 cm of extra rainwater in the top one-third meter of soil. To more fully understand the implications of this, we offer the following chart with normal water-holding capacity of various soils:

SOIL TEXTURE READILY AVAILABLE MOISTURE PER 30 CM (1 FT)

Light, sandy: Coarse sand 1.8 cm (0.7 in)

Fine sand 2.3 cm (0.9 in)

Medium, loamy: Fine sandy 3.8 cm (1.5 in)

Silt loam 4.8 cm (1.9 in)

Heavy, clay: Clay 5.1 cm (2.0 in)

Clay loam 5.3 cm (2.1 in)

In summary, we are able to increase the water-holding capacity of various soils from two to five times, and probably even higher. And we are experimenting with newer, higher rate systems under DeWitt Sunbelt (weed barrier) in which we can increase the water-holding capacity of coarse sand by more than ten times! The cost is high, but it can be done!

Rooftop Rain Stored in Polymer-Loaded Soil

A light 0.6 cm (0.25 in) rain on a 190 sq. meter (2,000 sq ft) roof will capture 118 deciliters (310 gallons) which can be absorbed and stored in polymer-loaded vegetable beds located near a building. For instance, collection of rainfall from a 200 sq. meter roof into a 50 sq. meter (2150 to 540 sq ft)vegetable bed will not only increase overall annual rainfall by 400%, but the polymer storage will allow its use as needed through the growing season. A one-month dry period might require considerable irrigation for a traditional garden, but a polymer-loaded bed of equal size connected to a rooftop collection system could be designed to hold enough water to carry the vegetable garden through the one-month drought.

Experimentation with such rooftop collection/polymer storage systems is just beginning in the American West, but it appears to hold considerable promise. Whether or not it will prove economical is not yet known, but I urge each agricultural research facility to design a small polymer-loaded test plot (i.e., 10 sq. m – 108 sq ft) to raise vegetables from water collected from a facility building rooftop. The goal in each case should be total dryland vegetable gardening, regardless of annual rainfall, with no supplemental irrigation. The following sketch shows a proposed polymer-loaded, dryland vegetable bed which absorbs and stores water from a rooftop collection system.

Rooftop water catchment supplies polymer-loaded garden bed.

ADDITIONAL AGRICULTURAL AND AGROFORESTRY USES FOR CLP

Drill Seeding Native Grasses

Some limited efforts have been made in the Western United States to use CLP (specifically HydroSource Standard, 2-4 mm -.08 to .16 inches – in size) mixed with the grass seed for drill-seeding. We are aware of more than 500 acres of this type seeding with rates ranging from 10 to 50 kg per ha (9-45 lbs./ac). As long as the seeder understands that the polymer must be hydrated (either with rain or irrigation water) to keep the seedrow moist during the roughly two-week germination window, the technique works well.

Some efforts with only limited success have been made to use a fine grind of CLP (i.e., HydroSource Fine) to mix with moistened seed as a form of seed-coating.

Possibly one of the most promising proposed techniques for stand establishment of native grasses has not yet been tried (to the best of my knowledge), but would be reasonably easy to test. With some type of squeeze pump or plastic bag, squeeze out a 3-cm-wide, 1/2-cm-deep (1.2 X 0.2 in) stream of hydrated gel (HydroSource Fine), and lay seeds on top of the gel before covering it with a thin layer of soil.

Russian olive (Elaeagnus angustifolia) seedling one year after being bareroot transplanted with 1/2 liter hydrated HydroSource Standard in the planting hole. (Castle Rock, Colorado)

Seedling Tree Survival Plantings with Polymer

Millions of seedlings are now planted in the Western United States by bareroot-dipping the seedling roots with a CLP slurry (made from powdered – 0.5mm (.02 in) – polymer) and mixing a cup to a pint of hydrated standard (2-4 mm – .08-.16 in) CLP in the planting hole around the root system. If no rain follows the planting, the seedling can survive for 1-2 months on the water in the polymer. Per seedling cost of this type planting US$ 0.03 (3 cents) for the standard polymer and $ 0.005 (1/2 cent) for the bareroot dip.

The seedling of the future will likely be grown in a polymer/soil mix (possibly 10% polymer to 90% soil?), bareroot-dipped after lifting and transplanted to the field with 100-200 hydrated granules (US$ 0.005 to $ 0.01 – 1/2 to 1 cent). In addition, the polymer granules will likely be pre-loaded with Ani-Pel, a systemic, biodegradable animal repellent. WPI is currently involved with at least five such projects to grow seedlings in a polymer mix (two with the U.S. Forest Service, two in Canada, one in Volgograd, Russia, and a planned project with the Ministry of Forestry in Ankara, Turkey.) (Ani-Pel contact: Amar Grewal, ASG Consultants, 7868 11th Avenue, Burnaby, British Columbia, V3N 2N3, Canada, telephone and FAX (604) 521-0864.)

Based on some preliminary experience with Ponderosa pine (Pinus ponderosa) seedlings, we believe the technique holds great potential for decreasing seedling transplant mortality worldwide. For this reason, we recommend each nation start such tests – using soil mixes containing 10%, 20%, and 30% hydrated polymer.

Direct Seeding and Aerial Reseeding

More than 100,000 pelletized seeds have been spread by aircraft and by hand in British Columbia, Canada, over the past three years, with success rates from 40% to as high as 70%. The small pellets contains 45% CLP, some phosphate as a crude germination trigger, and various types of conifer seed. The pellets are placed dry, but swell to 7.5 cm (3 in) in diameter after exposure to water during one of the very frequent rains there, thus providing the seeds with a growing medium which includes sufficient moisture. But using current technology, only a few rainy sites in the world would benefit from this type of seeding, which requires a moist climate.

A new type of direct seeding effort may hold greater promise. A 7.5-cm (3-in) wide polymer-loaded wafer containing a tree seed is physically dropped into a liter-sized hole and a liter of water is added. The wafer, which contains 5% CLP swells quickly (within 2-3 minutes) to provide a water-storing growth medium for the seeds. We have constructed some prototype pellets, and believe the technology is workable.

Loading Polymers with Pesticides and Herbicides

Cross-linked polyacrylamide is an excellent carrier for water-soluble pesticides and herbicides. Simple loading can be accomplished by using dry granules to hydrate the solution. For small basic tests, this loaded, hydrated polymer can be mixed in soil, and dehydration is not even necessary. For instance, in 1989, a Colorado State university researcher diluted liquid garlic 50% with water, placed it in infant wheat rows and got a 50% reductions in Russian aphid damage.

Liquid from the neem tree (Azadirachta indica), and other anti-insect natural compounds would likely work in this same manner. Researchers should also grind up allelopathic trees, shrubs or weeds to test as natural herbicides. Here in the U.S. ponderosa pine needles and the hulls of the black walnut (Juglans nigra) would be likely candidates for initial research. Such granules loaded with allelopathic liquids might be raked into the ground around a freshly-planted seedling to prevent grass and weed intrusion.

For those researchers interested in nematocides , bacteria, etc., the concept is the same. In addition, we are aware of 1-2 tests in which significant increases in mycorrhizal activity resulted from the use of cross-linked polyacrylamide, during planting.

Worms

Because polymer/soil beds retain moisture longer and keep soil loose, initial tests at 5 kg per 100 sq. m (10.3 lbs./1,000 sq ft)incorporated into the ground 20 cm (8 inches) in a Utah test apparently resulted in significant increases in worm production.

SUMMARY

Longevity

A good-quality, modern 400X sodium-based cross-linked polyacrylamide should last 7-10 years in a garden, and I have some which still perform fairly well after 5 years and 8 months in a Colorado garden. This high-quality polymer has been taken through 100 freeze/thaw cycles with little obvious deterioration in performance, and is relatively resistant to breakdown by fertilizer. UV damage is not a concern for polymer underground (but will slowly attack polymer in hydrated form on the surface).

Soluble salts in irrigation water and the ground will often reduce the hydration capacity from its 400X potential to 180-300X. This latter fact is important when building polymer collection systems, as performance will be highest in rainfall collection beds, and lowest when irrigating with water containing high concentrations of soluble salts.

Because of cross-linked polyacrylamide’s (400X product) exceptional longevity and durability, we continue to feel it will have an important place in agriculture of the future, especially in marginal rainfall areas where it’s difficult to utilize the small amount of rainfall that does reach the land. CLP is proving to be a very complex material in designing correct application rates and methods for the different plants. Tremendous research is still ahead in many aspects of CLP’s behavior, and we welcome your input and efforts.

WPI is a small, research oriented company with limited financial assets, but we have the experience, technical capability, and desire to assist foreign research facilities with considerable technical support. WPI now has more than 2500 pages of documents on the subject of cross-linked polyacrylamide – probably the largest such collection in the world – and serves as an informal clearinghouse to assist researchers both in the U.S. and abroad. Currently, we make copies of selected documents, but sometime in the future we plan to computerize our entire document collection.

We can supply very small amounts of CLP or Continuem Nutra-Gel, but request you either purchase larger amounts or approach major aid-providing organizations (i.e., U.S.A.I.D., or the World Bank) to obtain it on your behalf.

We cannot afford to pay for international travel, but if expenses can be covered I am interested in spending a week in specific countries, traveling and briefing on the subject of cross-linked polyacrylamide. In May 1992, for example, my 11-year-old daughter and I visited Turkey on behalf of a small Turkish company. I gave about 15 briefings and demonstrations to key university and government researchers, and we drove more than 800 miles through Turkey as part of the briefing process. We also gave the Turkish company approximately 600 pages of key documents, and hope to return in the future to attend a proposed national conference which will gather Turkish researchers working with CLP.

For researchers with questions, please FAX or airmail the queries to me. I will respond quickly with a letter and/or documents in the requested channel (FAX or airmail).

WORLDWIDE RESEARCH SUGGESTIONS FOR CROSS-LINKED POLYACRYLAMIDE IN AGRICULTURAL RESEARCH