Abstract

Two separate experiments were conducted to investigate plant growth and mineral composition of potatoes (Solanum tuberosum L.) at varied solution concentrations of nitrate (NO₃ ^‐) and ammonium (NH₄ ⁺). Each experiment evaluated five nitrogen (N) concentrations of 0.5, 2, 4, 8, and 12 mM, which were maintained with a non‐recirculating nutrient film system in controlled environment. Plants were harvested on day 42 with NO₃ ^‐ and day 35 with NH₄ ⁺ after transplanting of tissue culture plantlets, and growth measurements were taken as leaf area, tuber number, and dry weights of different parts. With NO₃ ^‐, plant growth was greatest and similar at 2, 4, and 8 mM of N whereas with NH₄ ⁺, plant growth was best only at 2 and 4 mM of N. At 12 mM of N, plants exhibited interveinal ammonium toxicity with NH₄ ⁺ nutrition, but healthy growth appearance with NO₃ ^‐ nutrition. With either N form, total N concentrations in tissues tended to increase with increased N concentrations, and tissue phosphorus (P) concentrations were reduced at 0.5 and 2 mM of N. Tissue concentrations of calcium (Ca), magnesium (Mg), and sulfur (S) changed only slightly at particular N concentrations, yet changed substantially with different N forms. The data indicate that the optimal ranges of N concentrations in both solution and tissues are wider and higher with NO₃ ^‐ than with NH₄ ⁺ nutrition, and thus a careful control of NH₄ ⁺ concentrations is necessary to minimize possible ammonium toxicity to potato plants.