Response of Potatoes to nitrogen concentrations differ with nitrogen forms

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.