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Liang Cheng, Ning Zhang, and Bingru Huang

The accumulation of 1-aminocyclopropane-1-carboxylate (ACC), which is a precursor for ethylene production, in plant roots exposed to salinity stress can be detrimental to plant growth. The objectives of this study were to determine whether inoculating roots with bacteria containing deaminase enzymes that break down ACC (ACC-deaminase) could improve plant tolerance to salinity in perennial ryegrass (Lolium perenne) and to examine growth and physiological factors, as well as nutrition status of plants affected by the ACC-deaminase bacteria inoculation under salinity stress. Plants of perennial ryegrass (cv. Pangea) were inoculated with either Burkholderia phytofirmans PsJN or Burkholderia gladioli RU1 and irrigated with either fresh water (control) or a 250 mm NaCl solution to induce salinity stress. The bacterium-inoculated plants had less ACC content in shoots and roots under both nonstressed and salinity conditions. Salinity stress inhibited root and shoot growth, but the bacterium-inoculated plants exhibited higher visual turf quality (TQ), tiller number, root biomass, shoot biomass, leaf water content, and photochemical efficiency, as well as lower cellular electrolyte leakage (EL) under salinity stress. Plants inoculated with bacteria had lower sodium content and higher potassium to sodium ratios in shoots under salinity stress. Shoot and root nitrogen content and shoot potassium content increased, whereas shoot and root calcium, magnesium, iron, and aluminum content all decreased due to bacterial inoculation under salinity treatment. ACC-deaminase bacteria inoculation of roots was effective in improving salinity tolerance of perennial ryegrass and could be incorporated into turfgrass maintenance programs in salt-affected soils.

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Timothy K. Broschat

Hong Kong orchid tree is an outstanding flowering tree for tropical and subtropical areas, but in south Florida’s nutrient-poor sand soils, it typically develops moderate to severe K and Mg deficiency symptoms during the fall, winter, and spring months. A 3-year field experiment was conducted to determine if flowering was responsible for the development of these deficiencies and to determine if these deficiencies could be prevented by fertilization with medium or high rates of a 24N–0P–9.2K turf fertilizer (24–0–11) an 8N–0P–10K–4Mg plus micronutrients palm fertilizer (8–0–12) or a 0N–0P–13.3K–6Mg plus micronutrients palm fertilizer (0–0–16). Onset of deficiency symptoms coincided with the beginning of flowering, but leaf nutrient concentrations of N, P, K, and Mg continued to decline after flowering ceased in late January, presumably because of movement of these elements from the leaves to stem tissue. Leaf nutrient concentrations were poorly or negatively correlated with all measured plant quality variables and were poor indicators of plant quality or nutritional status. Although fertilization with a high rate of 24–0–11 or either rate of 8–0–12 increased tree height, caliper, and number of flowers, no treatment significantly decreased the severity of K and Mg deficiencies.

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R.S. Mylavarapu, J.P. Smith, and F. Munoz

High temperature and humidity during summer months in the southeastern U.S., in addition to crop nutritional status, are suggested to be the primary reasons for tipburn incidence in collards (Brassica oleracea Acephala Group) adversely affecting their marketability. A 2-year study was conducted to evaluate the efficiency of grower's standard practice (GSP), GSP + gypsum, and a programmed-release fertilizer (PRF) under conventional and deep tillage on collard yield and tipburn incidence. Subsoiling significantly increased yield over conventional tillage. Nutrient supply through PRF did not increase the yields; however, it resulted in either similar or higher levels of macro- and micronutrient levels both in soils and collard tissue compared to GSP and GSP + gypsum treatments. The occurrence of tipburn in collards is dependent on several factors, including nutritional, physiological, and environmental stresses. Regression analyses of tipburn ratings at harvest time and the soil and tissue nutrient content suggested that 47% of the variation could be attributed to soil and tissue levels of sulfur (S), zinc (Zn), and phosphorus (P). It is important, therefore, to ensure an optimum supply of nutrients to the plants to maintain the quality of the yields. The advantage of PRF in sandy soils, and identification of other factors affecting the tipburn in collards should be further investigated.

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Harvey J. Lang

Analysts of potting media for pH and electrical conductivity (EC) can be a useful tool for monitoring the nutritional status of greenhouse grown plants. This research examined the variability associated with procedures involved in the determination of pH and EC in greenhouse potting media. Three commonly used methods, the 1:5 dilution, the 1:2 dilution and the saturated media extract, were examined on several different commercial potting media. Because of the different dilution volumes used, there were significant differences in pH and EC between the three methods for all media tested. Within each method, results varied baaed on whether readings were taken in the slurry, solution phase, or extract, with extracts resulting in consistently higher pH, but lower EC values. There was a significant effect of medium-solution equilibration time on both pH and EC, with variability decreasing after 30 minutes of equilibration. Samples taken from the upper half of pots had higher EC readings than those collected from the bottom half of pots only on plants fertilized with N concentrations greater than 200 ppm. There was also slight variability between the different calibrated instruments used in determining pH and EC. Details of each study along with grower recommendations will be discussed.

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Amy J. Compton and Paul V. Nelson

Many plug seedling growers complain about the inadequacy of substrate testing as a measure of nutritional status because results are too variable. We conducted two experiments to test a model system of sampling substrate at a set time after fertilization. Petunias (Petunia×hybrida Hort. ex Vilm. var. multiflora `Primetime White') were grown in 288-cell plug trays. Six fertilizer regimes were used consisting of a factorial arrangement of three fertilizer cycles (at each, every other, and every third irrigation) and two leaching fractions (0% and 20%). Fertilizer or water was applied at 0900 HR daily, and then 24 hours later in Expt. 1, and 1 hour later in Expt. 2, substrate solutions were sampled and analyzed. Samples taken after waterings were used to assess the dilution and leaching effects of water on substrate nutrient concentrations. In Expt. 2, additional substrate samples were taken at various hours after fertilizing to test the effect of plant depletion of the substrate. Substrate nutrient concentration curves constructed from data drawn at a fixed time after fertilizations, but not after waterings, were logical and could be interpreted. When data from a fixed time after fertilizations and waterings were plotted together, the curves could not be interpreted. Data from samples taken at various hours after fertilization in Expt. 2 revealed large reductions in concentrations, often after only 4 hours. Overall, leaching and dilution effects from watering in combination with the increased time span from fertilizing to sampling resulted in nutrient concentrations that could not be interpreted. Substrate testing can be effective for plug seedling production, but samples need to be taken 1 to 2 hours after fertilizations.

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Yan Chen, Kimberly A. Williams, Brent K. Harbaugh, and Michelle L. Bell

Host-plant nutritional status may affect the incidence and development of western flower thrips (WFT; Frankliniella occidentalis Pergande). Two greenhouse experiments were conducted to determine the responses of WFT population levels on impatiens (Impatiens wallerana Hook.f.) when plants were fertilized with commercially practiced rates of nitrogen (N) and phosphorus (P). Impatiens `Dazzler Violet' were grown with nutrient treatment combinations of 2 N rates (8 and 20 mm) by 2 P rates (0.32 and 1.28 mm). Individual plants grown in thrips-proof cages were inoculated with WFT at 2 or 4 weeks after transplant, in separate experiments, representing vegetative or reproductive stages of plant growth, respectively. Plants were destructively sampled weekly for 4 weeks following inoculation. Plant tissue N and P concentrations were significantly different across treatments: 8 and 20 mm N resulted in 4.9% and 6.3% N in tissue, respectively; 0.32 and 1.28 mm P resulted in 0.37% and 0.77% P in tissue, respectively. Nitrogen rates had no effect on WFT population levels. However, 4 weeks after inoculation with adult female WFT during the vegetative growth stage, plants fertilized with 1.28 mm P had more adult WFT than those fertilized with 0.32 mm P. Feeding damage varied depending on whether plants were inoculated in the vegetative stage with adult WFT or during reproductive growth with immature WFT. Plant size and number of flowers were lower in plants inoculated during the vegetative growth stage with adult WFT but were not affected when inoculation with immature WFT occurred during the reproductive stage, as most WFT were found feeding inside the nectariferous spurs of the flowers. Tissue N was lower in WFT-inoculated plants compared to noninoculated plants in both experiments.

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Wenhe Lu, Kathleen Haynes, Eugene Wiley, and Beverly Clevidence

The yellow pigment in potato (Solanum L. sp.) tuber flesh is caused by various carotenoids that may protect against cancer, cardiovascular disease, and macular eye degeneration. The objectives of this research were to 1) identify and quantify the carotenoids present in 11 diploid clones from a hybrid population of Solanum phureja ssp. phureja Juz. & Bukasov-S. stenotomum ssp. stenotomum Juz. & Bukasov and two tetraploid potato cultivars (the yellow-fleshed `Yukon Gold' and the white-fleshed `Superior'), and 2) determine the relationship between tuber yellow intensity and carotenoid content. Yellow intensity was measured by a colorimeter programmed to calculate a yellowness index, YI E-313. Carotenoid analyses were performed on an automated high-performance liquid chromatography system with software for integration and quantitation with detection at 450 nm using a diode array detector. Six major carotenoids were detected: neoxanthin, violaxanthin, lutein-5,6-epoxide, lutein, zeaxanthin, and an unknown carotenoid. Total carotenoid content in the yellow-fleshed diploid clones was 3 to 13 times higher than `Yukon Gold' and 4 to 22 times higher than `Superior'. Both total and individual carotenoid contents were positively correlated with tuber yellow intensity. There was an exponential relationship between total carotenoid content and tuber yellow intensity. This suggests that selecting for more intense yellow flesh will result in higher levels of carotenoids. These specific diploid clones were selected for this study because they produced at least five percent 2n pollen; they have the potential to make significant contributions to improving the nutritional status of tetraploid potatoes through 4x-2x hybridizations.

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Sean M. Westerveld, Alan W. McKeown, Cynthia D. Scott-Dupree, and Mary Ruth McDonald

With the introduction of nutrient management legislation in Ontario, there is a need to improve the efficiency of nitrogen (N) utilization. One possibility is to use critical nutrient concentrations in plant tissue as an indicator of the N nutritional status of the crop. Plant tissue analysis was used to determine the total N and nitrate-N (NO3-N) concentrations of cabbage (Brassica oleracea var. capitata L.), carrots (Daucus carota L.), and onions (Allium cepa L.) grown in Ontario. The tissue samples were collected from plants as part of N fertilization studies from 1999 to 2001 on the organic soils in the Holland/Bradford Marsh area and the mineral soils near Simcoe, Ontario. Yield was assessed at harvest as an indicator of the N requirement of the crop. Testing the usefulness of critical NO3-N concentrations to indicate the N requirement of the crop was problematic because: 1) few published references were available to indicate a critical level of NO3-N in these crops; 2) tissue NO3-N concentrations were highly variable; and 3) field data rarely matched published references. Tissue total N concentrations from the trials corresponded to published critical N concentrations in some cases, however, the use of published critical N concentrations would have resulted in either over or under-application of fertilizer to the crops. Cultivar, soil type, and climate were shown to affect tissue N concentrations. Based on these results it was concluded that local research and field verification is required before tissue N critical nutrient concentrations become useful for determining fertilizer needs of cabbage, carrots, and onions grown in Ontario.

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Archana P. Pant, Theodore J.K. Radovich, Nguyen V. Hue, and Susan C. Miyasaka

Previous work has demonstrated the potential of compost tea to enhance plant growth and nutritional status. One factor thought to contribute to variability in the efficacy of compost tea is the amount of compost per unit volume of water. To address these gaps in our understanding, two greenhouse trials and two field trials were conducted to investigate the effects of various extraction ratios on the growth, mineral nitrogen (N), and phytonutrient content of pak choi (Brassica rapa, Chinensis) and on soil biological properties. In greenhouse experiments, plants were fertilized with a single rate of chicken manure-based thermophilic compost. In field trials, three fertilizer treatments: 1) rendered meat byproduct or Tankage (Island Commodities, Honolulu, HI); 2) soluble fertilizer (16:16:16); and 3) chicken manure-based thermophilic compost were applied. Aerated vermicompost teas were prepared using chicken manure-based vermicompost and water at various ratios. Pak choi plants were treated weekly for 4 weeks with 10%, 5%, 3%, and 1% vermicompost teas in the greenhouse experiments and 10% and 5% teas in the field trials. Applications of vermicompost tea significantly increased plant growth, N content, total carotenoids, and total glucosinolates in plant tissue; this response was greatest in chicken manure-fertilized treatments. Increases in yield and phytonutrient content were associated with increased N uptake. Vermicompost tea also increased soil respiration and dehydrogenase activity over the control (water). Plant growth, phytonutrient content, and microbial activities in soil increased with increasing concentrations of vermicompost tea. Within the range of concentrations evaluated (1%–10%), greatest plant growth response was observed with 5% and 10% vermicompost tea, indicating that the optimal water-to-vermicompost ratio for extraction is lower than 50:1 and is likely in the range of 10:1 to 20:1. The findings suggest that vermicompost tea could be used to improve plant nutrient status and enhance soil biological properties in vegetable production.

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Frank J. Peryea, Denise Neilsen, and Gerry Neilsen

The recommendations for boron (B) sprays in deciduous tree fruit orchards have changed little over the past 50 years. We conducted two 3-year field studies evaluating the effect of two modifications to the existing recommendation for B maintenance sprays on apple (Malus ×domestica) tree nutritional status. A widely recommended Na polyborate-based commercial B spray product was used as the B source. Postbloom sprays of B applied at the recommended annual B maintenance rate of 0.56 kg·ha-1 to `Scarlet Gala' apple trees consistently increased fruit B concentration but had a weaker effect on leaf B concentration in early August, the recommended timing for sampling leaves for mineral element analysis. Applying half or all of the annual B maintenance rate in a spray at the pink flowering stage increased flower cluster and early-season leaf B concentrations as well as having positive effects on fruit and leaf B concentrations. The pink sprays increased flower cluster Na concentration but had no effect on leaf and fruit Na concentrations. In the second study, one-quarter of the annual B fertilizer requirement was tank-mixed with each of four biweekly CaCl2 sprays applied starting in early June for bitter pit control. This treatment consistently increased `Scarlet Gala' fruit B concentration but had a lesser effect on August leaf B concentration. It did not interfere with fruit Ca status, and increased both fruit and leaf Na concentrations. Leaf Na concentration in all treatments was substantially lower than levels associated with specific Na toxicity of deciduous fruit trees. The results of these experiments indicate that applying B sprays at the pink flowering stage timing and tank-mixing B with CaCl2 sprays applied for bitter pit control are useful practices to enhance B spray efficacy and convenience of application.