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Rhuanito S. Ferrarezi, Arun D. Jani, H. Thomas James III, Cristina Gil, Mark A. Ritenour, and Alan L. Wright

-drained soil in Central Florida showed that CRF and microsprinkler fertigation resulted in similar foliar N concentrations in young sweet orange orchards ( Morgan et al., 2009 ). In our study, fertilization rates followed the UF/IFAS recommendation on a per

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Xiaojie Zhao, Guihong Bi, Richard L. Harkess, Jac J. Varco, Tongyin Li, and Eugene K. Blythe

due to a dilution effect by greater amount of reserve N from the previous year. ‘Immortality’ TB iris is capable of repeat blooming in a growing season; however, the second bloom was largely influenced by N fertilization rate in the year of flowering

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Juan C. Díaz-Pérez, Albert C. Purvis, and J. Thad Paulk

Bolting causes significant economic losses in sweet onion (Allium cepa L.) production. Although temperature and photoperiod are considered to be the main factors that initiate bolting in onions, preliminary results suggested that low N fertilization rates increased bolting. The objective of our study was to determine the relationships of bolting, yield and bulb decay with N fertilization rates. The N fertilization rates applied ranged from the infraoptimal to the supraoptimal (from 102 to 302 kg·ha-1 N). Shoot and bulb N content increased with increasing N rates, but there were no differences in the respective shoot and bulb N contents among cultivars. Bolting incidence declined steadily with increasing N fertilization rates up to 197 kg·ha-1 N. Bolting incidence was among the highest in the cultivar Pegasus. The percent of decayed bulbs also increased at a steady rate with the rate of N applied. Total (14.7 t·ha-1) and marketable (0.8 t·ha-1) yields at the lowest N rate (102 kg·ha-1 N) were lower (P ≤ 0.01) than those at higher N rates. Rates of N ≥145 kg·ha-1 had no significant effect on either total (mean = 33.6 t·ha-1) or marketable (mean = 21.6 t·ha-1) yields. Losses in marketable yield were primarily a combination of bolting and bulb decay and were minimized at 162 kg·ha-1 N. Yield losses at low N rates were mostly due to bolting while yield losses at high N rates were mostly due to decay. Thus, excess applications of N fertilizer should be avoided since they have little effect on yields or bolting but they increase bulb decay.

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Brian E. Whipker and P. Allen Hammer

`Supjibi' poinsettias (Euphorbia pulcherrima Willd.) were grown hydroponically for 15 weeks in nutrient solutions with 100-15-100, 200-30-200, or 300-46-300 (in mg·L-1 of N-P-K) to determine nutrient uptake patterns and accumulation rates. Results indicate that increasing fertilization rates from 100 to 300 mg·L-1 of N and K did not significantly influence the plant dry mass or the nutrient concentration of P, K, Ca, Mg, Na, B, Cu, Fe, Mn, Mo, and Zn in poinsettias. NH4-N concentration in the leaves, stems, and roots were lowest with the 100-mg·L-1 N fertilization rate and increased as the N application rate increased to 200 and 300 mg·L-1. Leaf P concentration levels from 1 week after potting through anthesis were above 1.3%, which exceeds the recommended level of 0.9%. When the plant tissue dry mass for each fertilizer rate was transformed by the natural log and multiplied by the mean tissue nutrient concentration of each fertilizer rate, there were no significant differences among the three fertilization rates when the total plant nutrient content was modeled for N, P, or K. Increasing the fertilizer application rate above 100 mg·L-1 N and K and 15 mg·L-1 P decreased total plant content of Ca, Mg, Mn, and Zn and increased the total plant Fe content. The results of the weekly nutrient uptake based on the total plant nutrient content in this study suggests that weekly fertilization rates should increase over time from potting until anthesis. Rates (in mg) that increase from 23 to 57 for N (with 33% of the total N supplied in the NH4-N form), 9 to 18.5 for P, 19 to 57 for K, 6 to 15 for Ca, and 3 to 8 for Mg can be applied without leaching to poinsettias and produce adequate growth in the northern United States.

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Yan Chen, Regina Bracy, and Allen Owings

Annual vinca, Catharanthus roseus, is exceptionally adaptive to the summer heat and the sandy loam or clay soil in the southeastern region and provides season-long blooms once established in landscape plantings. A wide variety of colors, sizes, and applications are available for landscape use. However, diseases such as alternaria leaf spot and phytophthora leaf blight are prevalent in this region in vinca plantings. Effective disease control requires frequent fungicide application that is expensive and may pose negative effects on the environment. Proper planting techniques including date of planting, fertilization rate at planting, and variety selection may improve plant growth, reduce disease severity, and save landscape service business labor in disease management. Plants of three varieties: open-pollinated `Cooler Hot Rose', F1 hybrid `Titan Rose', and trailing variety `Mediterranean Lilac' were planted on 1 Apr. or 1 May in landscape plots. Plants were at the same growth stage at the time of planting and were fertilized with Osmocote 14–14–14 (3 months) at 0, 35, 70, or 140 g·m2. Plant growth index indicates that plant growth increased significantly at increasing fertilization rates; however, plant overall quality ratings were not significantly different among fertilized plants. Disease incidence in July suggests that late planting may reduce alternaria leaf spot in open-pollinated and hybrid upright type vinca. Disease severity in August was more pronounced on trailing vinca and more severe when plants were not fertilized or fertilized with the highest fertilization rate. Tissue analysis indicates that trailing vinca `Mediterranean Lilac' may require less fertilization than upright type.

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George H. Clough

In a 3-year study on a fine sandy loam soil, potato (Solanum tuberosum) cvs. `Atlantic' (1989), `Frontier' (1990, 1991) and `Russet Burbank' (1989-1991) response to rate and time of Ca fertilization was evaluated. Calcium was applied preplant at 0, 90, 180, and 270 kg·ha-1 as CaSO4 and side-dress at lay-by at 0, 67 and 134 kg·ha-1 as Ca(NO3)2, with treatments combined in a complete factorial. Preplant Ca fertilization increased soil Ca each year. Calcium fertilization had little effect on yield or grade distribution. Tuber P, K and S concentrations increased with increasing preplant and sidedress fertilization rates in 1989. Concentrations of S and Ca in Russet Burbank and Frontier increased linearly with preplant CaSO4 application rate in 1990 and 1991. Little or no internal brown spot (IBS) occurred in Atlantic or Russet Burbank, but in Frontier IBS was reduced both years by pre-plant and/or side-dress Ca application. The incidence of IBS did not change after storage for 4 months for any cultivar. In 1990, Russet Burbank fry color improved as pre-plant Ca fertilization rate increased.

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John Seliga, Vernon Shattuck, and Russel Johnston

A study was conducted from 1989 to 1991 to examine the effects of continuous tomato cropping, short-term crop rotation and, nitrogen fertilization rates on processing tomato quality. Research was conducted at two sites in southwestern Ontario, Leamington and Dresden, in split-plot experimental design. The rotations included tomato (Lycopersicon esculentum) - winter wheat (Triticum aestivum) (underseeded with red clover (Trifolium pratense), tomato-winter wheat-soybean (Glycine max), tomato-alfalfa (Medicago sativa), and tomato-rye (Secale cereale). Nitrogen fertilization rates of 0, 45, 90 and 135 kg/ha were used. Processing tomato cv. Heniz 9230 and Nabisco Brands Ltd. 7107 were assessed for colour, % soluble solids and total solids, and blossom end rot [BER]. In most instances, continuous tomato [C-T] had significantly poorer colour, soluble solids, and total solids than fruit from the various crop rotations. High nitrogen rates for C-T at Leamington, resulted in improved soluble solids and total solids, but had no significant effect on colour. A lower incidence of BER consistently occurred with low rates of nitrogen. Our results indicate that short-term crop rotation and nitrogen management in processing tomatoes can enhance fruit quality when compared to C-T.

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Robert H. Stamps

Established leatherleaf fern was grown for one year in a glasshouse in intact soil columns (Astatula fine sand, 21 × 61 cm) contained in drainage lysimeters. Columns were fertilized at rates of 224, 448, or 672 kg N ha-1 yr-1 using controlled-release (CR) fertilizer, either 360-day (360CR) or 180-day (180CR) term, or weekly applications of liquid (L) fertilizer. Water use, yield (number of harvestable fronds) and average frond weight increased linearly with increasing fertilization rate and more fronds were produced using L than CR fertilizers. Frond color measurements paralleled yield results. During cool weather when vase life is greatest, fronds from L fertilizer lysimeters lasted longer than fronds from CR treated plots. During warmer weather, treatments had no effect on vase life. Nitrate nitrogen (NO3-N) leaching increased with fertilization rate and exceeded 10 ppm in leachate from the L and 180CR treatments at all application rates. NO3-N in leachate from 360CR lysimeters never exceeded 8 ppm at any application rate.

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Shravan K. Dasoju and Brian E. Whipker

Pot sunflowers (Helianthus annuus cv. `Pacino') were fertigated on ebband-fl ow benches with 100 or 200 mg·liter–1 of N to determine the influence of fertility level on plant growth and postharvest quality in interior conditions. The fertilization rates were held constant from potting until day 45, then the fertilization rates were continued, decreased, or ceased on day 45 and day 55, giving a combination of nine fertilization subtreatments. At bloom, the number of days from potting to flowering, plant height, plant diameter, flower diameter were recorded, and the root medium of five replicates per treatment were analyzed to determine the nutrient status. Five replicates of each treatments also were moved into interior conditions with artificial lighting and were graded 5, 10, and 15 days after moving to evaluate the postharvest quality. There was no significant difference among fertilizer treatments for the number of days to flower, plant height, or flower diameter. Plants fertilized with 100 mg·liter–1 N from potting until day 45, in combination with a ceasing of fertilization on day 55, had significantly better plant grades when compared to plants grown with 200 mg·liter–1 N. Plants fertigated with 100 mg·liter–1 N also had a longer postharvest life and the number of days before the flowers wilted were significantly longer. Good-quality plants with longer postharvest life were produced with 100 mg·liter–1 N and by terminating fertilization 55 days after potting.

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Peter C. Andersen, Fred M. Rhoads, Steven M. Olson, and Brent V. Brodbeck

`Colonial' tomato (Lycopersicon esculentum Mill.) plants were grown on raised beds with black polyethylene mulch, drip irrigation, and preplant-N rates of 0, 67, 134, 202, or 269 kg·ha-1. Petiole sap was collected 7 and 13 weeks after transplanting. Concentrations of NO3-N, free amino acids, total amino acids, and total-N (the sum of NO3-N and amino acid-N) were examined as functions of the rate of N fertilization. Also, each of these compounds was used as an independent variable as a predictor of fruit yield. Seven weeks after planting, the concentrations of NO3-N and 15 of 18 of the free amino acids were correlated with the rate of N fertilization, but concentrations of bound or total amino acids were not. The amount of NO3-N accounted for 37% of the total-N in the 0 kg·ha-1 treatment, and up to 83% in the 202 kg·ha-1 treatment. NO3-N was highly correlated with total-N for both nonhydrolyzed and hydrolyzed sap (R 2 = 0.98). Thirteen weeks after transplanting, neither the concentration of NO3-N nor that of amino acids, other than asparagine, glutamine, and proline, were significantly related to the rate of N fertilization. On both dates, concentrations of glutamine plus glutamic acid were correlated with rate of N fertilization whether expressed as absolute values or as percentage values. N fertilization rate and the concentration of NO3-N or total-N were related to total fruit yield (R 2 = 0.69 to 0.74), and marketable fruit yield (R 2 = 0.78 to 0.82). N-fertilization rate and petiole sap concentrations of NO3-N or total-N were also correlated with the N contained in total or marketable yield. Petiole sap variables measured 13 weeks after transplanting were not significantly correlated with fruit yield or the quantity of N contained in the fruit. Free, bound, or total amino acids in petiole sap were not as well correlated with fruit yield parameters as were N-fertilization rate, NO3-N, or total-N in petiole sap.