Quantificação de amônia volatilizada de fontes nitrogenadas aplicadas em cobertura na pastagem

Abstract

Nitrogen (N) is one of the most limiting nutrients for vegetative growth and one of the most demanded by forage plants. However, the application of urea on the soil surface can cause N losses by volatilization of ammonia (NH3), which reduces the efficiency of N use by grasses. The objective was to quantify the volatilization of NH3 after the application, in coverage in Brachiaria brizantha cv Marandu, of nitrogen sources. The experiment was conducted at the Federal University of Mato Grosso, in the city of Barra do Garças - MT, in randomized blocks, with eight treatments (1-Urea (46N); 2-Ammonium nitrate (34N); 3-Ammonium nitrate ( 34N) and potassium sulfate as a source of sulfur (18S); 4-Ammonium nitrate (34N) and calcium chloride as a source of calcium (24Ca); 5-Ammonium nitrate with calcium and sulfur (27N; 5Ca; 3, 7S); 6- Ammonium nitrate with calcium and magnesium (27N; 4Ca; 2Mg) 7-Urea NBPT (32N); 8-Control); and four repetitions. The applied dose was 60 kg ha-1 of N, on December 4, 2022. Each plot had an area of 30 m2 . The capture of volatilized NH3 was carried out using a SALE-type collector, which consisted of a transparent plastic bottle (PET) with a capacity of 2 L and an area of 0.008 m2 . Inside the bottle, there was an 80 mL plastic pot containing a solution of sulfuric acid plus glycerin and a strip of polyethylene foam soaked in this solution. The soaked foams were the means of capturing the volatilized NH3, these were collected 1, 2, 5, 9, 14 and 20 days after the treatments were applied, later the data from each collection were added to obtain the total capture of volatilized ammonia . The data were subjected to analysis of variance and when the F test was significant, they were analyzed using the Skott knott mean test at 5% probability. The losses of N-NH3 occurred mainly with the urea sources and with the NBPT source, being 4.57 and 4.05 kg ha-1 of NH3 in the sum of the six collections. However, the use of urea with urease inhibitor did not provide reductions in ammonia losses by volatilization in relation to common urea, applied at a dose of 60 kg ha-1.