The objectives of this study were to examine the influence of nitrate, ammonium and ammonium + N-Serve on ionic balance and N uptake by maize plants. Maize plant were grown in calcareous soil supplied with 100 and 200 mg N kg^-1 soil in the forms of KNO₃, (NH₄)₂SO₄ (AS) and (NH₄)₂SO_{4 +} Serve (AS+NS) and sampled at 30 and 60 day after sowing (DAS). Results revealed that at different growth stages, the combination of ammonium sulfate with nitrapyrine (N – Serve) gave the highest value of dry matter and N uptake as compared with other treatments. Application of N – Serve with ammonium sulfate resulted in  decreasing the accumulation of NO^-₃ in maize leaves. NO^-₃ concentration was higher at 60 DAS than that found at 30 DAS and at 200 mg N/kg soil than 100 mg N/kg soil except when N–Serve was applied. Ratio of (K⁺/Ca²⁺ + Mg²⁺) was constant with all treatments which increased with ammonium sulfate + N–Serve treatments (AS + NS). Total uptake of inorganic cations and anions were determined by analysis of tissue for K⁺, Ca²⁺, Mg²⁺, Na⁺, total N, NO^-₃, SO⁼₄, PO⁼₄ and Cl^-. Differences in total inorganic cations (C) and anions (A) in plant tissue were used to estimate total carboxylate (C-A). Internal OH^- generation resulting from excess cation uptake (net H⁺ excretion) by the roots. The (C-A) of plant supplied 100 mg N/kg soil ranged from 85 to 116 at 30 DAS and 130 to 149 at 60 DAS. The increments in nitrogen levels tended to increase total cation uptake especially, with plants fed with ammonium + N-Serve. The increase in cation uptake was paralleled by an increase in anions uptake.  The C to A uptake ratio for plants supplied with 200 mg / kg soil ranged from 2.9 to 3.4 at 30 and 60 DAS, respectively, indicating that the internal OH^‑ was generated both by excess of cation uptake and by NO^-₃ and SO⁼₄ reduction. On a seasonal basis, only 15 % of the OH^- generated during NO^-₃ and SO⁼₄ reduction was associated with OH^- efflux (excess anion uptake), and 85 % was associated with carboxylate accumulation.