Volatilização da amônia de fontes e doses nitrogenadas aplicadas sobre o capim-marandu

Abstract

The role of nitrogen (N) in pastures is fundamental to minimizing the effects of degradation, however, the problem with the use of nitrogen fertilizers, especially urea, is the volatilization of ammonia (NH3), with average losses of up to 50%. The objective was to quantify N-NH3 losses after application of N doses and sources on Brachiaria brizantha cv. Marandu in the second year of cultivation. The experimental design adopted was randomized blocks, with five doses of N: 0, 60, 120, 180, 240 kg ha-1 of N in the sources urea and ammonium nitrate, with four replications totaling 40 plots; and in parallel with this experiment, six sources of N were tested at a dose of 120 kg ha-1 of N, namely: urea, ammonium nitrate, ammonium nitrate plus calcium and magnesium, ammonium nitrate plus calcium and sulfur, ammonium nitrate more calcium and ammonium nitrate plus sulfur, in addition to the control with four replications, totaling 28 plots. Each experimental plot was 30 m². The applications were carried out by broadcast divided into four applications of 60 kg ha-1 of N, for the experiment with doses, and for the experiment with sources, two doses of 60 kg ha-1 of N were applied at a time. Volatilized ammonia was collected by SALE's chambers on days 1, 2, 5, 9, 14 and 20 after the application of each dose of fertilizers and quantified by distillationtitration. The data were subjected to analysis of variance and when significant at 5%, the Skott-knott mean test was performed for qualitative analyzes (sources) and regression for quantitative analyzes (doses). Urea obtained the highest NH3 volatilization averages compared to the other applied sources, and adjusted linearly in the regression model, that is, NH3 volatilization was greater with increasing N doses. The greatest loss of NH3 of urea was obtained at a dose of 240 kg ha-1 of N, with 38.55 kg ha-1 , corresponding to 29.50% losses in relation to the N applied, the losses of NH3 (%) of ammonium nitrate adjusted In the quadratic regression model, the greatest losses were observed at a dose of 133 kg ha-1 of N, with 6.41% loss in relation to the N applied. Urea showed greater volatilization compared to other sources.