ARS | Publication request: Boron distribution and the effect of lime on boron uptake by pansy, petunia, and gerbera plants

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 15, 2010
Publication Date: May 19, 2011
Repository URL: http://hdl.handle.net/10113/50045
Citation: Krug, B., Whipker, B., McCall, I., Frantz, J. 2011. Boron distribution and the effect of lime on boron uptake by pansy, petunia, and gerbera plants. Acta Horticulturae. 891:135-140.

Interpretive Summary: Greenhouse growers will be interested in this research because it addresses the importance of proper chemical distribution to minimize high pH which leads to Boron deficiencies. Inadequate substrate mixing and plug cell-to-cell variation are not the cause of variable plug quality within a plug tray. Reports of boron (B) deficiency have become more prevalent in pansy, petunia, and gerbera plug production. When symptoms are observed, the presence and severity of symptoms have no pattern, with symptomatic plants located adjacent to asymptomatic plants in the same plug flat. It has been observed by many that the availability of B in the soil decreases as soil pH increases. Therefore, pansy, petunia, and gerbera seedlings were grown in a peat:perlite substrate that was amended with finely ground limestone at a rate of 6, 8, 10, or 20 lbs per cubic yard. As the rate of lime incorporated into the substrate increased so did soil pH and shoot tissue concentrations of Ca while shoot tissue concentrations of B decreased. Many commercially available germination substrates are amended with macro and micro nutrient fertilizers. Relatively small amounts of each element are incorporated into the substrate and uneven mixing could result in varying amounts of nutrients in individual cells of a plug flat. This variability could lead to nutrient deficiencies early in the crop cycle. Six commercially available germination substrates were used to fill plug flats and individual cells were sampled and analyzed for B concentrations. Of the substrates tested, there was no variation in B concentration from cell to cell. While the pH-caused boron suppression or deficiency was observed in this study, variable limestone mixing or substrate incorporation does not appear to be the cause of the variable symptoms during production.

Technical Abstract: Reports of boron (B) deficiency have become more prevalent in pansy (Viola ×wittrockiana), petunia (Petunia ×hybrida), and gerbera (Gerbera jamesonii) plug production. When symptoms are observed in production the presence and severity of symptoms have no pattern, symptomatic plants can be located adjacent to asymptomatic plants in the same plug flat. The availability of B in the soil decreases as soil pH increases. 'Yellow Dynamite' pansy, 'White Storm' petunia, and 'Festival Apricot' gerbera seedlings were grown in a peat:perlite substrate which was amended with pulverized dolomitic limestone at a rate of 6, 8, 10, or 20 lbs/yd3. As the rate of lime incorporated into the substrate increased so did soil pH and shoot tissue concentrations of Ca while shoot tissue concentrations of B decreased. Many commercially available germination substrates are amended with macro and micro nutrient fertilizers. Relatively small amounts of each element are incorporated into the substrate and uneven mixing could result in varying amounts of nutrients in individual cells of a plug flat. This variability could lead to nutrient deficiencies early in the crop cycle. Six commercially available germination substrates were used to fill plug flats and individual cells were sampled and analyzed for B concentrations. Of the substrates tested, there was no variation in B concentration from cell to cell.