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James M. Spiers

In a sand culture study, increasing Na levels increased leaf concentration of Na, Mg, Ca, Mn, and Zn, and reduced leaf K and plant dry weight. Magnesium fertilization did not affect leaf concentration of Ca, K, Mn, Fe, or Zn. High Ca fertilization increased leaf Ca. At high Mg levels, Ca fertilization had a synergistic influence on Mg uptake. Ca and Mg fertilization did not independently influence plant vigor, chlorosis symptoms, or dry weight production of leaves and stems. As levels of Na fertilization increased, plant vigor and leaf production decreased and chlorosis symptoms increased. With low Na fertilization levels, high Mg fertilization reduced leaf production but with high Na fertilization, plants receiving high Mg levels produced twice the weight of leaves as those with low Mg fertilization. High Mg fertilization reduced the detrimental effects of high Na fertilization on plant growth. This effect may be due to the antagonistic influence of Mg fertilization on Na uptake at high Na fertilization levels.

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James M. Spiers

The effects of varying potassium and sodium fertilization levels on 'Shawnee' blackberry (Rubrus, subgenus Eubatus, spp.) plant growth and leaf elemental content were studied in sand culture experiments. Increasing K fertilizer levels linearly increased K, but decreased Mg and Zn in the leaves. Concentrations of Na, Ca, Cu. Fe, and Mn were not significantly influenced by K fertilization. Plants contained six times more Na with high than with low Na fertilization. Na fertilization did not significantly affect leaf K, Ca, Mg, Fe, Cu or Zn, but leaf Mn was linearly reduced by increasing Na fertilization. Leaf K and Na were directly influenced by the amounts of supplied K and Na. 'Shawnee' blackberries readily take up Na but exhibit some salt tolerance at low to moderate Na fertilization levels. At high Na levels, they appear to lack a mechanism to reduce Na uptake, which results in reduced plant growth.

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James M. Spiers

In a 1989 field study, `Gulfcoast' southern highbush blueberry plants were subjected to irrigation [8 liters per week (low) and 30 liters per week (high)], mulching (none and 15 cm height), row height (level and raised 10-15 cm), and soil incorporated peat (none and 15 liters in each planting hole) treatments at establishment. Plants were grown on a well-drained fine sandy loam soil that contained < 1.0% organic matter. Plant volume was increased by either mulching, high irrigation, incorporated peat moss or level beds. Fruit yields were not significantly affected by irrigation levels but were highest with either mulching, level beds or incorporated peat moss. The bed height X mulching interaction indicated that mulching increased yield more with level beds than with raised beds. Plants grown with the combination of mulching, level beds, incorporated peat moss, and high irrigation levels yielded 1.1 kg per plant or approximately 10 times more than plants grown without mulch, with raised beds, without peat moss, and with the low rates of irrigation. Of the 4 establishment practices evaluated, mulching had the greatest influence on plant growth and fruiting.

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James M. Spiers

Five muscadine grape (Vitis rotundifolia) cultivars (`Carlos', `Doreen', `Magnolia', `Pineapple' and `Summit') were grown in sand-peat-pine bark (1:1:1) medium and fertilized with a complete marco- and micronutrient solution plus added Na. Plant growth plus mineral uptake in 4 plant parts (leaves, terminal stems, basal stems and roots) were measured. Top growth (leaves plus stems) was highest in `Pineapple' and lowest in `Doreen'. Root growth was higher in `Carlos' and `Doreen' and lowest in `Magnolia'. Plant part X cultivar interactions were significant for elemental Ca, Mg, Na, Fe, Zn, Cu, and Mn. Iron tended to be concentrated in the roots and leaves. Leaves and upper stems contained more K than the lower stems and roots and K concentrations were higher in `Carlos' and `Magnolia' than the other cultivars. Sodium content tended to be higher in the leaves than in the other plant parts. Little differences were present in Na uptake by the 5 cultivars.

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James M. Spiers

A sand culture study arranged in a 3 × 3 factorial was used to determine the influence of Al and Mn levels on leaf nutrient content and plant growth of `Tifblue' rabbiteye blueberry (Vaccinium ashei Reade). Aluminum fertilization increased leaf Al content but did not affect plant vigor, leaf dry weight, or chlorosis. Manganese fertilization resulted in increased Mn in the leaves and a decrease in all growth parameters measured. The Al × Mn interactions were significant for Mn concentration in the leaves and vigor ratings. At the highest Mn fertilization rate, increasing Al fertilization had a synergistic influence on leaf Mn. Plant vigor at the highest Mn rate was lowest when no Al fertilizer was added. Increasing Al fertilization resulted in better plant vigor in plants grown with a high rate of Mn fertilization.

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James M. Spiers

The effects of varying rates of a complete fertilizer and irrigation on the growth and fruit yields of `Tifblue' rabbiteye blueberries (Vaccinium ashei Reade) established 3 years before treatment initiation were determined in a field study. Increased rates of irrigation resulted in increased plant growth and fruit yields. Five- and 6-year-old plants were more responsive to increasing irrigation rates than older plants. Irrigation water efficacy was greatest at lower rates and progressively less at higher rates of irrigation. Five- and 6-year-old plants fertilized with the lowest rate (14N–4P–7K; 150 g/plant) grew and yielded less than those fertilized with higher rates. Older plants did not respond to fertilization rates higher than 150 g/plant. Yearly rates of fertilization above 300 g/plant did not influence plant growth or fruit yields. Fertilization and irrigation responses were independent.

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James M. Spiers

A greenhouse study was conducted to evaluate the influence of substrate temperatures (16, 27, and 38C) on root and shoot growth of six blueberry (Vaccinium spp.) clones (three clones each of two types). Between types, southern highbush (primarily V. corymbosum L.) produced more roots and total growth than rabbiteye (V. ashei Reade). Comparing clones, `Gulfcoast' (southern highbush) was the most vigorous and `Tifblue' (rabbiteye) the least vigorous. Each clone had a negative linear response to substrate temperatures in all growth characteristics. Root and shoot growth was best at 16C. This study indicates that both rabbiteye and southern highbush blueberries would respond favorably to cultural practices that lower soil temperatures during the summer growing season.

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James M. Spiers

In a field study, `Gulfcoast' southern highbush blueberry plants were subjected to irrigation [7.5 L (low) or 30 L per week (high)], mulching (none or 15 cm depth), row height (level or raised 15 cm), and soil-incorporated peatmoss (none or 15 L in each planting hole) treatments, in a factorial arrangement, at establishment. Plants were grown on a well-drained fine sandy loam soil that contained <1.0% organic matter. Plant volume and fruit yield were greater with mulching, high irrigation, incorporated peatmoss, and level beds. Plants grown with the combination of mulching, level beds, incorporated peatmoss, and high irrigation levels yielded 2.4 kg per plant or approximately eight times as much as plants grown without mulch, with raised beds, without peatmoss, and with the low rate of irrigation. Of the four establishment practices evaluated, mulching had the greatest influence on plant growth and fruiting.

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James M. Spiers and John H. Braswell

The effects of varying N, Ca, and Mg fertilization levels on plant growth and leaf elemental content of `Sterling' muscadine grapes (Vitis rotundifolia Michaux) were studied in a 2 year sand culture experiment. Increased N levels reduced leaf K, Ca, and Mn and increased leaf N and P concentrations plus plant growth. Calcium fertilization increased leaf Ca, decreased leaf Mg, but did not affect plant growth. Mg fertilization reduced leaf K and Ca and increased leaf Mg plus plant growth. Visual symptoms, assumed to be Mg deficiencies, were decreased by Mg fertilization and highly correlated to leaf Mg content. Plants which received the highest Ca fertilizer level had fewer deficiency symptoms when treated with the highest rate of N. Calcium fertilization tended to slow both Mg uptake and deficiency symptoms reductions caused by increases in levels of applied Mg. Growth of `Sterling' muscadine plants was positively correlated to leaf N and Mg and negatively related to leaf K, Ca, Mn, Zn, and Cu concentrations.

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Creiehton L. Gunton and James M. Spiers

The role of phosphorus (P) in magnesium (Mg) translocation from roots to leaves of muscadines (Vitis rotundifolia Michx.) was investigated in shadehouse experiments. Vines of 13 clones were grown for two seasons in sand culture fertilized with nutrient solutions containing no P (-P), 20 PPM P (+P), and -P plus P added during the two weeks before harvest (-P+P). Leaves were sampled at the end of each growing season and in July of the second year and analyzed for P, potassium (K), and Mg content. Mg and K contents of roots were determined at the end of the second year. No interactions occurred between clones and P fertilization levels for Mg or K content, indicating no differences among clones in response of these minerals to P treatments. Leaf Mg content was slightly but significantly lower for -P than +P treatments in the `92 and July `93 samples but about rhe same in September `93. Root Mg content in September `93 was higher for +P than -P or -P+P. No evidence was found that Mg translocation from root to leaves was mediated by P. No Mg deficiency symptoms were visible on the leaves for any treatment.