Effect of interactions between ammonium and nitrate on the growth physiology of groundnutPeanut is a crop of great importance for the Northeast region, as it is usually grown by small farmers, who on average, do not exceed 10 ha of cultivated area and aim to increase its profitability and diversify the production. This study aimed to evaluate the effect of the relationship between nitrogen forms (ammonium and nitrate) in the initial growth of peanuts. Complete nutrient solution was used with a single concentration of 210 mg N L -1 provided in five proportions of NH 4 + :NO 3 -: 100:0, 75:25, 50:50, 25:75 and 0:100. The experimental units were arranged in completely randomized design, with four replications. The variables evaluated were: shoot length, root length, leaf number, stem diameter, fresh and dry shoot and fresh weight and dry root. The 100:0, 75:25 and 50:50 ratio resulted in decreasing peanut phytomass by ammonium toxicity. However, the 0:100 ratio, nitrate caused a smaller decreased compared to reductions in the highest ammonium concentrations. In the 25:75 and 0:100 ratio, plants grow normally with higher phytomass. The supply of nitrogen in the NH 4 + form only is not a good option for the nutrition of peanuts in early growth stages.