AMMONIUM AND NITRATE NUTRITION OF 11 BEDDING PLANT SPECIES

An experiment was conducted to determine the best NH₄⁺:NO₃^- ratios for the growth of 11 bedding plant species in a greenhouse with daily average air temperatures 14–22C and CO₂ enrichment at 600–1,000 ppm. Seedlings were grown in cellpacks (5.5 cm x 6.0 cm x 5.5 cm) containing the Colorado State Univ. soil mix (1 soil:3 sphagnum peat:2 pearlite, v/v, steamed) with nutrient solutions (pH 6.50) containing 0, 25, 50, 75 and 100% NH₄⁺ in combination, respectively, with 100, 75, 50, 25 and 0% NO₃^-. In all solutions, nitrogen and total ion concentration were fixed at 16 and 50 meq·l^-1, respectively.

Most species grew best with mixtures of NH₄⁺ and NO₃^-: begonia, coleus, impatiens, marigold, petunia, salvia and zinnia at 50:50 (%), and snapdragon at 25:75 (%). However, ageratum grew best with 100% NH₄⁺, celosia with 100% NO₃^-, and lobelia with either 100% NH₄⁺ or 100% NO₄^-, NH₄⁺ toxicity symptoms were observed only in marigold and salvia grown with 100% NH₄⁺. Number of plants flowered in begonia, lobelia, petunia and salvia was not significantly different among treatments.