Influence of ammonium,nitrate, and chloride on solution pH and ion uptake by ageratum and salvia in hydroponic culture

The influence of nitrogen (N) forms and chloride (Cl) on solution pH and ion uptake in the hydroponic culture of Ageratum houstonianum [ammonium (NH₄ ⁺)‐tolerant] and Salvia splendens (NH₄ ⁺‐sensitive) for a period of 216 hours was investigated. The pH of the hydroponic solution (initially 6.50) containing either NH₄ ⁺ or NH₄ ⁺+nitrate (NO₃ ^‐) was drastically lowered (3.08), whereas that of the same solution containing NO₃ ^‐ was raised (7.74). Solution pH changed more by ageratum than by salvia. The solution Cl^‐ concentration did not influence pH significantly. However, addition of Cl^‐ in the solution lowered transpiration rate in both NH₄ ⁺ and NO₃ ^‐ treatments. Total N uptake was the greatest in the NH₄ ⁺ + NO₃ ^‐ treatment and the lowest in the NO₃ ^‐treatment. In the NH₄ ⁺ + NO₃ ^‐ treatment, NO₃ ^‐ uptake was suppressed by NH₄ ⁺ (to about 50%), while NH₄ ⁺ uptake was not affected by NO₃ ^‐. The rate of Cl^‐ uptake was the lowest in the NH₄ ⁺ treatment, but was similar in the NH₄ ⁺ + NO₃ ^‐ and NO₃ ^‐ treatments. Uptake of potassium (K⁺), dihydrogen phosphate (H₂PO₄ ^‐), sulfate (SO₄ ^‐2), manganese (Mn⁺²), and zinc (Zn⁺²) was significantly enhanced in the NH₄ ⁺ treatment. The uptake rate of calcium (Ca⁺²) and magnesium (Mg⁺²) was the highest in the NO₃ ^‐ treatment. Absorption of copper (Cu⁺²) and boron (B) was not affected by N source. Ion uptake was more stable in the solution containing both NH₄ ⁺ and NO₃ ^‐ than in the solution containing either NH₄ ⁺ or NO₃ ^‐. The uptake rate of total N, NH₄ ⁺, NO₃ ^‐, Mn⁺², Cu⁺², and Zn⁺² was higher, whereas that of Cl^‐ and molybdenum (Mo) was lower in ageratum than in salvia. Amounts of total anion (TA) and total cation (TC) absorbed, the sum of TC and TA, and the difference between TC and TA (TC‐TA) were affected by N source, Cl^‐ level, and their interactions. The NO₃ treatment, as compared to the NH₄ ⁺ or the NH₄ ⁺ + NO₃ ^‐treatment, reduced total cation and anion uptake while increasing TC‐TA, especially in the absence of Cl^‐. Plant tissue ion contents were also affected by N source and Cl^‐ level.