Solution pH, temperature, nitrate (NO3-)/ammonium (NH4+) ratios, and inhibitors effects on the NO3- and NH4+ uptake rates of coffee (Coffea arabica L.) roots were investigated in short-term solution culture. At intermediate pH values (4.25 to 5.75) typical of coffee soils, NH4+ and NO3- uptake rates were similar and nearly independent of pH. Nitrate uptake varied more with temperature than did ammonium. Nitrate uptake increased from 0.05 to 1.01 micromol/g FW/h between 4 and 16°C, and increased three-fold between 16 to 22°C. Between 4 to 22°C, NH4+ uptake rate increased more gradually from 1.00 to 3.25 micromol/g FW/h. In the 22-40°C temperature range, NH4+ and NO3- uptake rates were similar (averaging 3.65 and 3.56 micromol/g FW/h, respectively). At concentrations ranging from 0.5 to 3 mM, NO3- did not influence NH4+ uptake rate. However, NO3- uptake was significantly reduced when NH4+ was present at 3 mM concentration. Most importantly, total uptake(NO3- + NH4+) at any NO3-/NH4+ ratio was higher than that of plants fed solely with either NH4+ or NO3-. Anaerobic conditions reduced NO3- and NH4+ uptake rate by 50 and 30%, respectively, whereas dinitrophenol almost completely inhibited both NH4+ and NO3- uptake. These results suggest that Arabica coffee is well adapted to acidic soil conditions and can utilize the seasonally prevalent forms of inorganic N. These observations can help optimizing coffee N nutrition by recommending cultural practices maintaining roots in the temperature range optimum for both NH4+ and NO3- uptake, and by advising N fertilization resulting in a balanced soil inorganic N availability.