Progress 03/04/05 to 01/14/09
Outputs
Progress Report Objectives (from AD-416) To document silicon accumulation in various tissues of bedding plant species, to determine the silicon content of production growing media, to determine the best silicon source as an amendment, to assess the effects of silicon on horticultural traits, to determine the ability of silicon to suppress disease and pest attack, and to evaluate the effects of silicon on reducing rate or numbers of required pesticide applications. Approach (from AD-416) Screen the most popular bedding plant species to determine extent and location of silicon accumulation using SEM/X-ray dispersion and ICP analysis. Determine silicon content of production growing media using acetic acid extration and ICP. Evaluate the effect of silicon in accumulator species on horticultural traits and disease/pest protection. Determine the best silicon amendment sources and fertigation protocol. Evaluate the feasibility and potential benefit of silicon use in production settings. Significant Activities that Support Special Target Populations This report provides the final summary of research conducted by the cooperator to determine the uptake, accumulation, and potential benefit of silicon in bedding plant crops. An in-depth study of four representative horticultural crops has been conducted utilizing three comparative methodologies (SCM-EDXA, ICP, and colorimetric) to determine the silicon content of each crop grown in the presence of several levels of either mineral or solubilized formulations containing elemental silicon. Results were consistent between research locations and with comparative analytical methodologies to characterize the crops into three classes based on the amount of silicon detected. Dicotyledonous test crops Begonia sp., Impatiens sp., and Tagetes sp. (marigold) and a monocotyledon, Thysanolaena maxima (tigergrass) were evaluated utilizing two sources of calcium silicate (Wollastonite W-20 and Excellerator) or a liquid formulation of potassium silicate (AgSil 25) applied to soilless growing medium at different rates up to 1.87 kg elemental Si/m3. Of the four crops, only tigergrass demonstrated a statistically significant uptake of silicon but the dry weight of the plants supplied the highest rate of silicon (1.87 kg/m3) was lower than control plants not receiving silicon amendment. Tigergrass plants amended with Excellerator and Wollastonite had 4.9 and 4.4 times the percent silicon relative to control plants and plants amended with AgSil 25 had 2.1 times the amount of silicon as control plants but there was no significant difference in dry weight between the different treatments. These results support and confirm findings in the parent project which utilized a hydroponic approach to evaluate silicon uptake and accumulation with a larger group of ornamental crops. Evaluation of the beneficial role of silicon in disease suppression utilizing two high-accumulator crops is on-going in the parent project to elucidate the mechanism of action which will provide potential for reduced fungicide application in achieving acceptable disease control. Evaluation of fertigation, using soluble silicon, and media amendment using both mineral and organic materials, are being compared to determine a commercially acceptable approach to fortify bedding plants with silicon during production. These accomplishments address NP-305, Component I, Problem C. This project has been monitored primarily by periodic email and phone exchanges and an annual face-to-face meeting with the PI in conjunction with attendance at a national or international scientific meeting.
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Progress 10/01/05 to 09/30/06
Outputs
Progress Report 4d Progress report. This report serves to document research conducted under a Specific Cooperative Agreement between ARS and the University of Florida. Additional details of the research program can be found in the report for the parent CRIS 3607-21000-011-00D Develop Improved Technologies for Soilless Greenhouse Plant Production to Minimize Water, Labor, Agrochemical Inputs and Environmental Impacts. Experiments have been designed to determine the optimal conditions to grow four ornamental bedding plant crops (Begonia, Dianthus, Impatiens, and Marigold) in a soilless medium to which silicon (Si) amendments are added to determine Si uptake and accumulation in the various plant tissues. Initial results were inconsistent so further studies were undertaken which documented that a significant amount of the available Si was leached out of the growth medium in as little as one week. Both sources of Si (Wollastonite and Silical) tested were leached whether
watering was done from above or through subirrigation. Water management was determined to be critical in determining Si accumulation in the test plants. In initial studies with Salvia (S. gregii), the highest Si amendment rate (4000 kg Si/ha) resulted in tissue accumulation of Si of 0.235% compared to 0.089% without Si addition. Si accumulation was determined by colorimetric analysis following digestion of plant tissues. These studies will be compared to research being done on the parent CRIS Project in which these plant species are exposed to Si in a hydroponic system or through fertigation using a similar soilless growing medium. Comparison of Si accumulation using comparative analytical methods (colorimetric, ICP, SEM/EDXA) will be undertaken using exchanged tissue samples.
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Progress 10/01/04 to 09/30/05
Outputs
4d Progress report. This report serves to document research conducted under a Specific Cooperatiave Agreement between ARS and the University of Florida Gainesville. Additional details of this research project can be found in the report for the parent CRIS 3607-21000-008-00D Develop New or Improved Methods of Hydroponic and Greenhouse Production and Pest Protection. This SCA officially began in March 2005 and since that time a graduate student, Asha Brunnings, has been selected and enrolled in a PhD program at the University of Florida. Experiments have been initiated towards finding a plant growth medium that will attain the correct pH (5.8-6.5) for ornamentals after addition of wollastonite, CaSiO3, as a Si source and/or CaCO3. Based on a preliminary test, an acidic peat (80%v/v) mixed with vermiculite (20%v/v) and 100 ml osmocote was chosen for the growth medium. Ornamental species (Begonia, Dianthus, Impatiens, Marigold, and Salvia gregii) were used in these
experiments with increasing levels of wollastonite (0, 2000, and 4000 kg/ha). Pots were equilibrated with respect to calcium by adding CaCO3, to pots with 0 or 2000 kg Si/ha. Salvia showed increased silicon content in both stems and leaves with increasing levels of wollastonite. The other species have been harvested, dried and ground in preparation for Si analysis. Ongoing experiments in the greenhouse involve Begonia, Dianthus, Impatiens, and Salvia spp. with the equivalent of wollastonite at 0, 1000, 2000 and 4000 kg/ha added to the growing medium. These studies will be compared to research being done on the parent CRIS in which the same species of bedding plants are exposed to Si in a hydroponic system or through fertigation using a similar soilless growing medium. Comparison of Si content using comparative analytical methods (wet chemistry, ICP, and SEM/SCA) will be undertaken using exchanged tissue samples.
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