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W.C. Fonteno and T.E. Bilderback

supported, in part, by erants from Industrial Services International and Aquatrols Corporation of America and the hydrogel used in this study is a commercial material distributed under the trade names “Terrasorb AG” and “SuperSorb C.” respectively. Technical

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Michael W. Olszewski, Marion H. Holmes and Courtney A. Young

suitable for 1.6- or 2.8-inch-deep substrates ( Getter and Rowe, 2009 ). Water-absorbent crystals, or hydrogels, expand into pliable gels when hydrated and are added to horticultural substrates to reduce plant stress and act as a water reservoir supply

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Max E. Austin and K. Bondari

Three field experiments were conducted to determine short- and long-term effects of hydrogel mixed with peatmoss, milled pine bark, or soil on growth and yield of blueberry. Rabbiteye blueberry cultivars (Vaccinium ashei Reade) Delite, Tifblue, and Climax, and southern highbush cultivar (V. corymbosum L.) Georgiagem were used as test plants. Hydrogel mixed with soil was detrimental to plant survival. Hydrogel with or without peatmoss or pine bark did not influence yield or berry weight of 3- to 4-year-old `Delite' and 2- to 3-year-old `Tifblue' plants. The southern highbush, `Georgiagem', grown in peatmoss + hydrogel, produced plants of larger volume than those grown in peatmoss alone. Yield or berry weight was not affected significantly by soil amendments. Genetic differences between cultivars affected growth, yield, and berry weight, but the cultivar x soil treatment interaction was not significant.

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Jennifer L. Boatright and J. M. Zajicek

Hydrogel (Hydrosource™, Western Polyacrylamide, Inc.) was incorporated into 102 cm × 122 cm landscape beds at 25, 50, 75, or 100 lbs per 1000 sq ft. Weed barrier and 2 cm of pine bark mulch were added to the top of each bed. Controls consisted of 1) no hydrogel with weed barrier and mulch and 2) no hydrogel with mulch but no weed barrier. Each treatment was replicated four times with ten plants of petunia, marigold, and vinca planted per bed, for a total of forty plants of each species per treatment. Flower number of vinca and petunia increased with hydrogel incorporation, 75 lbs of hydrogel having the greatest number of flowers. Petunia also had higher visual ratings with increased hydrogel rates. Soil temperatures directly under the mulch and 10 cm below the mulch, at 1400 hr, were 49C and 40C respectively for controls, compared to 42C and 36C for beds with hydrogel.

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Jeffrey H. Gillman*

Hydrogels are crystals that can suck up 600 or more times their weight in water. These gels are sold as additives for soils and container media for the purpose of reducing the frequency of watering. Five different hydrogels and a control were tested on geranium and 3 different hydrogels and a control were tested on ninebark to see how long plants could be kept healthy without watering. Growth was roughly similar among the control and the different hydrogels tested with the exception of Hydrosorb™, which stunted the growth of the ninebark. After plants reached a size that was considered saleable watering was stopped and the plants were allowed to dry out. None of the hydrogels kept the plants supplied with water for any longer than the controls. Hydrosorb™ did appear to keep ninebarks at a healthy water potential for longer than the other hydrogels and the control, however, this is almost certainly because of the smaller size of the plants.

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Daniel C. Bowman and Richard Y. Evans

Hydration of a commercial hydrophilic polyacrylamide gel in 20 meq Ca(NO3)2/liter was reduced to <10% of the maximum hydration in deionized water. Repeated soaking with deionized water to remove soluble salts restored hydration to ≈ 30% of maximum. Incorporating KNO3 at concentrations ranging from 5 to 40 meq·liter-1 with the Ca(NO3)2 in the hydration solution partially reversed the Ca2+ inhibition of hydration following repeated soaking. Potential hydrogel hydration increased to 50% of maximum with 40 meq K+/liter. Potassium nitrate supplied separately following hydration in Ca(NO3)2 was much more effective at reversing Ca2+ inhibition of hydrogel hydration than joint application. Potential hydrogel hydration (following repeated soaking) was doubled after treatment with 5 meq KNO3/liter and reached 77% of maximum at 40 meq KNO3/liter.

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Anthony Koski

The purpose of this study was to evaluate the effectiveness of soil-incorporated hydrogel to reduce irrigation requirements of transplanted Kentucky bluegrass (Poa pratensis) sod. The treatments included an untilled control, tilled soil, and tilled soil with incorporated hydrogel. Initial irrigation treatment were made daily, at various percentages of potential evapotraspiration (PET), to determine irrigation requirements of newly transplanted sod. Other irrigation treatments were later imposed on transplanted sod which had been established at 100% of PET, to determine irrigation requirements of established sod. Turf quality was measured weekly, and sod transplant rooting strength was also measured.

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Jonathan M. Frantz, James C. Locke, Dharmalingam S. Pitchay and Charles R. Krause

An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca2+ and Mg2+). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.

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Yin-Tung Wang and Lori L. Gregg

The levels of hydration of several hydrophilic polymers (hydrogels) varied greatly. Starch-based polymers had the fastest rate of hydration (<2 hours), followed by a propenoate-propenamide copolymer. Polyacrylamide materials required 4 to 8 hours to become fully hydrated. Maximum water retention in distilled water varied from 400 to 57 g of water per gram of dry material. All hydrogels retained less water in the presence of metal ions or fertilizers in the soaking solution, with substances releasing Fe+2 being the most detrimental. After exposure to fertilizers and ions, the water-holding capacity of a polyacrylamide with a high degree of cross linkage, but not that of hydrogels of the other structures, was fully recovered by subsequently soaking in distilled water. Pots amended with a polyacrylamide polymer but without Micromax (a micronutrient source) reached maximum water retention after six irrigations, while those with Micromax required 10 irrigations to reach peak water retention. The amounts of water being held in pots decreased after repeated fertilization. Medium volume increased with increasing levels of the polyacrylamide Supersorb C (0, 2, 4, or 6 g/pot). Micromax incorporated in medium amended with Supersorb C caused a depression in volume. Medium bulk density, total water retention, and water retention per unit volume of medium were increased by the incorporation of the hydrogel, regardless of the presence of Micromax. Noncapillary porosity measured at container capacity in medium amended with Micromax progressively decreased as the amount of hydrogel increased, but remained unchanged in medium without Micromax. Repeated drying and dehydration of the medium resulted in reduced water retention and increased noncapillary pore space.

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Patricia Newton Myers and Cary A. Mitchell

A copolymer acrylamide acrylate gel was investigated as the sole root matrix for dark-grown seedlings of soybean (Glycine max Merr. `Century 84'). Increasing Ca2+ in the hydrating solution of the hydrogel from 1 to 10 mm decreased its water-holding capacity from 97 to 46 mL·g-1, yet water potential of the medium remained high, sufficient for normal plant growth at all Ca2+ concentrations tested. Elongation rate of dark-grown soybean seedlings over a 54-hour period was 0.9, 1.5, and 1.8 mm·h-1 with 1.0, 2.5, or 5.0 mm Ca2+, respectively, but did not increase with further increases in Ca2+ concentration. Further study revealed that Na+ was released from the hydrogel medium and was taken up by the seedlings as Ca2+ increased in the medium. In dry hypocotyl tissue, sodium content correlated negatively with calcium content. Despite the presence of Na+ in the hydrogel, seedling growth was normal when adequate Ca2+ was added in the hydrating solution. Acrylamide hydrogels hold good potential as a sole growth matrix for short-term experiments with dark-grown seedlings without irrigation.