Comparison of hydroponic solutions for poinsettia nutritional studies1

Abstract

Poinsettia cultivars Supjibi and Freedom were grown in eight hydroponic solutions to develop a baseline solution for further nutritional studies. Four solutions contained nitrogen (N) from Ca(NO3)2‐4H2O and KNO3 (denoted as ‐NH4) and four contained Ca(NO3)2‐4H2O, KNO3, nitric acid, and NH4NO3 as the N sources (denoted as +NH4). The four ‐NH4 and +NH4 solutions were further divided by an IX or 2X rate of micronutrients [boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn)] (denoted as IX or 2X). A factorial of these four solutions at 2 concentrations (100 mg L1 of N and potassium (K) and 15 mg L1 phosphorus (P), or 300 mg L1 of N and K and 46 mg L‐1 P) was studied. Greater leaf and stem dry weight for both ‘Supjibi’ and ‘Freedom’ was observed in plants grown with the +NH4 solutions, with a larger increase occurring with’ Supjibi’. Leaf NH4‐N content for both cultivars was higher for both the 100 and 300 mg L‐1 N and K fertilization rates when NH4‐N was included. The leaf K content was highest for the plants grown with the +NH/2X solution for ‘Supjibi’, for both fertilization rates, and leaf K content increased as the K application rate increased. Results indicate that for nutritional studies with poinsettias, hydroponic solutions should include between 12.5% to 33% of the N in the NH4 form, a calcium magnesium (Ca:Mg) ratio of 2:1, and a micronutrient concentration of (mg I/1) 0.5, 0.02, 6.6, 0.5, 0.1, and 0.05, respectively, for B, Cu, Fe, Mn, Mo, and Zn, for adequate plant growth.