Calcium and bicarbonate effects on the growth and nutrient uptake of burley tobacco seedlings: Float system

High levels of bicarbonate (HCO₃^-) alkalinity have been shown to affect the growth and nutrient uptake of tobacco seedlings in solution culture. The objective of this study was to determine the effect of HCO₃^- on the nutrient uptake of burley tobacco seedlings grown in a float system. Float bays of a size to accommodate individual float trays were filled with 40 L of deionized water. A commercial 20-10-20 (20% N, 10% P₂O₅, 20% K₂O) water soluble fertilizer was added to give 100 mg N L^-1. Sodium bicarbonate and calcium chloride were added to provide a factorial combination of 5 levels of HCO₃^-(0, 122, 244, 366, and 488 mg L^-1 and three levels of calcium (Ca²⁺) (25, 50, and 75 mg L^-1). Pelleted burley tobacco seed (var. KY 907) were sown into 200-cell float trays filled with peat-vermiculite medium. Plants in all treatments appeared normal. HCO₃^- alkalinity above 244 mg L^-1 limited the growth of tobacco seedlings. Total nitrogen (N), phosphorus (P) and potassium (K) concentration in the shoot portion of tobacco seedlings the lowest at 244 mg L^-1 HCO₃^-, as compared t lower or higher HCO₃^- levels. Calcium concentration in shoots increased with increased HCO₃^-, but zinc (Zn) decreased and magnesium (Mg) and iron (Fe) were not significantly changed. Added Ca²⁺ had no significant effect on transplant growth. High nitrite-N concentrations were observed in the float water solution three weeks after seeding. Nitrite-N accumulation increased at high levels of HCO₃^-. Increased HCO₃^- alkalinity resulted in lower shoot nutrient concentrations, but the growth restriction due to HCO₃^- did not appear to be related to nutrient deficiency. However, transient levels of nitrite-N may have been sufficiently high to result in stunting of the tobacco seedlings.