PANSY FLORAL DEVELOPMENT AND NUTRIENT ABSORPTION AS INFLUENCED BY TEMPERATURE, NITROGEN FORM, AND STAGE OF PLANT DEVELOPMENT

Abstract

Production temperatures can affect the marketability of pansies (Viola × wittrockiana Gams.) by influencing plant growth, the presence of nutrient disorders, and the rate of floral development. The choice of nitrogen (N) form in fertility can also influence pansy growth and nutrition, but the effect of fertility on pansy flowering is not clear. Whether or not temperature and N fertility work together to influence nutrient absorption at different stages of the pansy life cycle is unknown. Our objectives were to determine the influence of temperature and N form on pansy floral development, and to identify the peak nutrient demand periods at different temperatures and ratios of NO₃ ⁻ to NH₄ ⁺ in fertility. Pansies cv. ‘Crown White’ were grown in nutrient solution cultures until lateral branches had open flowers. Treatments consisted of two temperatures (12°C and 22°C) and three stages of floral development (five true leaf stage until visible bud, visible bud until first flower, first flower until flowering on lateral branches), and three NO₃ ⁻ :NH₄ ⁺ molar % ratios (100:0, 62:38, 25:75) with a total concentration of 100 mg N L⁻¹. A modified Hoagland's solution was used with NO₃ ⁻−N supplied as Ca(NO₃)₂ and KNO₃ and with NH₄ ⁺−N as (NH₄)₂SO₄. The effects of temperature and N form on the time required for development of different floral stages were assessed. In addition, the influence temperature and N form on nutrient absorption was determined for three pre‐determined stages of floral development to identify peak nutrient demand periods. The timing of flower bud development and first flower was not influenced by treatments. At 22°C, pansies flowered earlier on lateral branches than at 12°C, but these plants also suffered a loss in quality due to unfavorable growth characteristics and the development of nutritional disorders. Individual absorption of plant nutrients at different stages of development varied with temperature and N regime. Overall, pansies absorbed the greatest quantity of magnesium (Mg) before flower bud development, calcium (Ca) after flower bud development, and NH₄ ⁺, NO₃ ⁻ phosphorus (P), and potassium (K) after anthesis. In addition, pansies absorbed more NO₃ ⁻, Ca, Mg, and P at 12°C than at 22°C. At times, the absorption of NO₃ ⁻ was dramatically decreased with increasing NH₄ ⁺ in solutions. Results suggest that nutrient absorption by pansy in different stages of development is influenced by production temperatures and the choice of N form in fertilization. Adjusting fertility programs according to peak demand periods and production temperatures will help prevent periodic nutrient disorders during the life cycle, and may reduce fertilization costs.

Acknowledgments