Nitrogen Source and Concentration Affect Growth and Performance of Bedding-plant Impatiens

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  • 1 Iowa State Univ., Horticulture, Ames, Iowa
  • | 2 Iowa State Univ., Horticulture, Ames, Iowa
  • | 3 Iowa State Univ., Horticulture, Ames, Iowa

Impatiens (Impatiens wallerana Hook. f.) is the most important annual bedding plant in the US, based on wholesale dollar volume. Production of high-quality plants requires optimization of the nutrition regimen during growth, especially the total nitrogen (N) concentration and the ratio of N sources. Our objective was to determine the N concentration and ratio of N sources that optimize bedding-plant impatiens growth and development. We used four N concentrations (3.5, 7, 10.5, and 14 mmol·L-1 of N) in factorial combination with four ratios of nitrate-N (NO3--N) to ammonium-N (NH4+-N) (4:0, 3:1, 1:1, and 1:3). Application of treatments began at day 30, and every-other-day applications were conducted until day 60. From day 60 to day 70 only deionized water was applied. N concentration and source displayed interation for most growth parameters. When N was supplied at a concentration ≤7 mmol·L-1, the NO3--N to NH4+-N ratio did not affect growth. When N was supplied at a concentration ≥10.5 mmol·L-1, a 1:3 NO3--N to NH4+-N ratio yielded the greatest shoot dry weight, shoot fresh weight, plant diameter, and number of flower buds per plant. With a NO3--N to NH4+-N ratio of 4:0, these growth parameters decreased. To produce high-quality, bedding-plant impatiens, N should be applied at NO3--N to NH4+-N ratios between 1:1 and 1:3 in combination with an N concentration of 10.5 mmol·L<-1 at each fertigation from day 30 to day 60 of the production cycle.

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