Growth Suppression and Raised Tissue Cl- Contents in NH4+-fed Marigold, Petunia, and Salvia

in Journal of the American Society for Horticultural Science
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  • 1 Department of Horticulture, Colorado State University, Fort Collins, CO 80523

Ageratum houstanianum Mill. (tolerant), Tagetes patula L. (French marigold, very sensitive), Petunia hybrida Vilm. (sensitive), and Salvia splendens F. Sellow et. Roem & Schult. (very sensitive) were grown with NO3-, NH4+NO3-, or NH4+ as the N source to examine whether NH4+-related growth suppression (NH4+-RGS) in the NH, -sensitive species was associated with excessive Cl- absorption from the nutrient solution. Amounts of Cl- applied were 4 or 11 meq·liter-1 (Expt. 1) and 0 or 4 meq·liter-1 (Expt. 2). When fertilized with NH4+ as a sole N source, marigold, petunia, and salvia showed NH4+-RGS symptoms with yield reduction regardless of altered Cl- levels in the nutrient solution, while ageratum showed no such symptoms. When grown with NH4+ solution, these sensitive plants had shoot fresh and dry weight reductions of ≈ 50% compared to those grown with the NH4+ + NO3- solution. Plants fertilized with NH4+ showed more severe NH4+-RGS symptoms when grown in rockwool (RW) than in peat-lite mix (PL). The NH4+-grown plants contained more NH4+ and much more Cl- in the tissue than plants fertilized with NO3- or NH4+ + NO3-, irrespective of the Cl- level in the nutrient solution. However; NH4+-RGS symptoms in marigold, petunia, and salvia appear to be caused by the uptake of NH4+, but not in association with Cl- from the nutrient solution.

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