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

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Abstract
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.