Effect of two Nitrification Inhibitors on Nitrate Accumulation in grass “ Elefant” Pennisetum purpureum Schum. In the Mario Gonzalez Aranda farm, wich is a property of National University of Colombia (Palmira-Valle) was realireJ an experiment intended to quantify the pricess of conversion of ammonium into nitrate in the ground and the concentrations of this ion on the Elefante grass, Pennisetum purpureum Schum. It was compared the grade of inhibition of two inhibitors products of the nitrification (Sulfatiazol, N-Serve) and the tendencies on the studieJprocess depending on the source (Urea, Nitron 26) and the quantity of nitrogen (100, 200 Kg N/Ha) applied on the grass. It was found that the concentrations of nitrats on the grounds and the vegetal tissue stretched to intensity at the same time as were increase the levels of nitrogenious fertilization and in some cases for the present environment conditions.