Hydrogel as a Field Medium

Three field experiments were c effects of hydrogel mixed with peatmoss, m of blueberry. Rabbiteye blueberry cultiva and Climax, and southern highbush culti used as test plants. Hydrogel mixed with drogel with or without peatmoss or pine b of 3to 4-year-old ‘Delite’ and 2to 3-year‘Georgiagem’, grown in peatmoss + hydro those grown in peatmoss alone. Yield or b soil amendments. Genetic differences bet berry weight, but the cultivar x soil treatm the most effective soil amendment for rabbiteye blueberry plants (Brightwell, 1971; Spiers, 1983). Spiers (1986) found that incorporated peatmoss tended to concentrate roots near the crown area and at depths of 30 to 45 cm. Also, highbush blueberry plants grew better when soil was amended with peatmoss (Haynes and Swift, 1986). Hydrogel granules were introduced by Agricultural Systems, Union Carbide Corp., in the late 1970s. These water-absorbing polymers or soil conditioners seem well suited for water stress studies, because they can absorb up to 130 to 150 times their dry weight in water (Union Carbide Corp., 1977). Super slurper, a hydrolyzed polyacrylonitrite graft copolymer, has decreased crust strength and infiltration and increased water retention of several soils (Hemyari and Nofziger, 1981). Bedding plants (Gehring and Lewis, 1980) and tomato ( Lycopersicon esculentum Mill.) transplants (Willingham and Coffey, 1981) Received for publication 2 Dec. 1991. Accepted for publication 3 Apr. 1992. Supported by state and Hatch funds allocated to the Georgia Agricultural Experiment Station. We thank J.S. Mason, Dept. of Horticulture, for his technical assistance in field work. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact. 1Professor, Dept. of Horticulture. 2Professor, Statistical and Computer Services Dept. HORTSCIENCE, VO L. 27(9), SEPTEMBER 1992 eberry Plants xperiment Station, Tifton, types, organic matter, rabbiteye blueberry, ducted to determine shortand long-term led pine bark, or soil on growth and yield (Vaccinium ashei Reade) Delite, Tifblue, r ( V. corymbosum L.) Georgiagem were il was detrimental to plant survival. Hyk did not influence yield or berry weight d ‘Tifblue’ plants. The southern highbush, l, produced plants of larger volume than ry weight was not affected significantly by een cultivars affected growth, yield, and nt interaction was not significant. grew better in media mixed with hydrophilic polymers than in media alone. Less irrigation was required for Ligustrum lucidum Ait. grown in hydrophilic polymer-amended medium than for plants in nonamended medium (Taylor and Halfacre, 1986). Stomata1 conductance and leaf water potential of young grapefruit (Citrus paradisi Macfad.) trees were higher 2 months after planting for trees in hydrogel-amended soil than for control trees, but no differences existed 1 month later (Swietlik, 1989). Conversely, one study (Gupton, 1985) showed that when four Vaccinium genotypes and the V. ashei cv. Tifblue were treated with hydrogel either alone or in combination with peatmoss, ≈ 25% of the plants died during the first year after transplanting. The present study was undertaken to compare the effects of hydrogel alone and in a mixture with peatmoss and pine bark on yield, berry weight, and growth of several blueberry cultivars. Effects of plant age, cultivar, and their interactions with soil treatments on plant performance also were investigated. Three experiments were conducted to evaluate short-term (Expts. I and II) and longterm (Expt. III) effects of hydrogel on blueberry growth, berry weight, and yield. Short-term, amendments, and soil (Expt. I). Bare-rooted, 2-year-old nursery plants of ‘Delite’ rabbiteye blueberry were planted in Mar. 1978 in a Leefield loamy sand (loamy, siliceous, thermic, Arenic, Plinthaquic Paleudults). Furrows were opened with a middle buster, and treatments consisting of 3 liters of various moist soil amendments were applied at each plant location. Plants were spaced 1.5 m in rows with 3.0 m between rows. Treatments were six soil amendments: 1) 3 liters of peatmoss (PM); 2) 3 liters of peatmoss mixed with Viterra 2 Hydrogel (Union Carbide Corp., Tuxedo, N.Y.) (PM + Gel) at the rate of 3.2 g·liter-1; 3) 3 liters of milled pine bark (PB); 4) 3 liters of pine bark mixed with 10 g of hydrogel (PB + Gel); 5) 20 g of hydrogel mixed with 3 liters of soil, incorporated into the soil 2 days before planting; and 6) 20 g of hydrogel incorporated into the soil at planting. The volume of hydrogel we used per plant was 42% less than recommended by the manufacturer (Union Carbide Corp., 1977), but hydrogel with soil alone was applied at the recommended rate. Experiment I, consisting of four replications and three plants/plot, was continued for two harvest years (1979 and 1980). In addition to total yield and berry weight, plant growth of ‘Delite’ was rated (0 = dead to 5 = excellent growth) in Jan. 1979 and Feb. 1980. Short-term, amendments, no soil (Expt. II). A similar experiment with four replications and five plants per treated plot was initiated in Mar. 1979 using 2-year-old ‘Tifblue’ rabbiteye blueberry plants. Treatments were the same as in Expt. I, except the hydrogel-soil treatments (Treatments 5 and 6 in Expt. I) were omitted. The experiment was for two harvest years (1980 and 1981), but plant growth was rated only in Feb. 1980. In Expts. I and II, plants were harvested with a hand-held vibrator and catching assembly. Berries were weighed and graded and percent marketable yield calculated. In all studies, berry weight was determined from the number of berries in a 100-g sample. Long-term (Expt. III). An experiment to determine the long-term effect of hydrogel on yield, growth, and fruit size was initiated in Mar. 1979. There were four replicates of two plants for each soil amendment. The soil was a Tifton loamy sand (fine-loamy, siliceous, thermic Plintiic Paleudults). The cultivars were rabbiteye ‘Climax’ and southern highbush ‘Georgiagem’. Only two soil amendments (Treatments 1 and 2 of Expt. I), peatmoss and peatmoss with hydrogel at the same rate described in Expts. I and II, were included in this experiment. Plants were grown under uniform cultural conditions for 11 years, and growth data (height, width, and breadth in centimeters) were then obtained from each plant in June 1989. Plant volume was computed as cubic meters from height x width x breadth. Stem length (average of eight terminal stems) was measured, and the number of leaf nodes was counted. Berries were hand-harvested in 1990. Statistical analysis. Data were first analyzed for each experiment separately as complete randomized block designs with subsampling. For Expt. III, data were first analyzed for each cultivar separately, and then data from both cultivars were combined to analyze for cultivar comparisons. The experimental error was tested over the sampling (residual) error. In the absence of a significant experimental error, the sum of squares for the two error terms was pooled