2019 ASHS Annual Conference

Silicon (Si) can alleviate abiotic and biotic stresses in plants. Substrate components and amendments, liquid fertilization, and foliar sprays can provide supplemental Si. Substrate amendments may supply an extended release of Si during production, but incorporation rates are not well elucidated. Our objective was to evaluate substrate amendments as potential Si sources for potted roses (Rosa ×hybrida). Amendments added to the peatmoss substrate included parboiled rice hulls at 5%, 10%, or 20% (by volume); ground parboiled rice hulls at 5%, 10%, or 20% (by volume); rice hull biochar at 1.5%, 3%, or 6% (by volume); steel slag (PlantTuff) at 2.37, 4.75, or 7.12 kg∙m^-3; hydrous potassium silicate (AgSil) at 0.38, 0.76, or 1.14 kg∙m^-3; and calcium silicate (wollastonite) at 0.39, 0.78, or 1.17 kg∙m^-3. A non-amended control and a non-amended control fertilized with 2 mM potassium silicate at each irrigation were also evaluated. Initial substrate pH of each treatment was adjusted to 6.2 – 6.5. Rooted liners of rose ‘Daniela’ were transplanted into 11.5-cm pots, arranged in a completely randomized design with five pots per treatment, and grown for six weeks. Greenhouse air temperatures were 20.4 ± 1.0 °C day/16.3 ± 1.4 °C night, with a daily light integral of 12.2 ± 1.1 mol·m^-2·d^-1. Plants were fertilized with 20N-2.2P-12.4K at a concentration of 150 mg∙L^-1 N at every irrigation. Plant growth and quality (height, dry mass, root rating, and relative chlorophyll content) of all treatments were similar to the non-amended control. Leachate Si concentrations for the non-amended control and the 2 mM liquid potassium silicate treatments were 4.4 and 54.0 mg∙L^-1 after 2 weeks, 1.2 and 76.8 mg∙L^-1 after 4 weeks, and 0.3 and 83.3 mg∙L^-1 after 6 weeks, respectively. Leachate Si concentrations of the amendment treatments ranged from 12.1 to 42.7 mg∙L^-1 after 2 weeks, 10.9 to 31.1 mg∙L^-1 after 4 weeks, and 3.2 to 15.4 mg∙L^-1 after 6 weeks. Foliar Si concentration ranged from 180 mg∙kg^-1 in the non-amended control to 4732 mg∙kg^-1 in the 2 mM liquid potassium silicate treatment, but between 500 and 2051 mg∙kg^-1 for the substrate amendment treatments. Foliar Si increased as incorporation rate increased.