Pot experiments were conducted on three soils differing in their ammonium (NH4+) fixation capacity [high = 161 mg NH4-nitrogen (N) kg(-1) soil; medium = 31.5 mg NH4-N kg(-1) soil; and no = no NH4-N was additionally fixed], and the effect of N fertilizer forms and doses on wheat (Triticum aestivum L.) was investigated. Grain yields responded to almost all forms of N fertilizer with 80, 160, and 240 kg N ha(-1) in the high, medium, and no NH4+ fixing soil process, respectively. Agronomic efficiency of applied N fertilizers was significantly greater in the no NH4+ fixing soil. Thousand grain weights (TGW) of wheat grown on the high and medium NH4+ fixing soil decreased with increasing N. Grain protein increased with increasing NH4+ fixation capacity. Nitrogen doses and the forms of N fertilizers affected grain protein at a significance level. The combination of urea + ammonium nitrate (NH4NO3) was most effective in increasing grain protein content.