Disponibilidad de forraje en praderas de pasto Xaraés en respuesta a fuentes de nitrógeno convencionales y tratadas con N-(n-butil) triamida tiofosfórica (NBPT)

The N-(n-butyl) thiophosphoric triamide (NBPT), a urease inhibitor, has been reported as one of the most promising compounds to reduce losses by volatilization, and to maximize the use of urea nitrogen (N) in agricultural systems. A field study was carried out to examine urease inhibitors' potential about volumetric density and forage mass grass (Brachiaria brizantha cv. Xaraés) to N application. The experiment was carried out from September 2017 to September 2018. The experimental design used was complete randomized blocks in the 3×2×4 factorial array, considering: three periods of the year (wet season, dry season, and the transition), two sources of urea (conventional urea and NBPT–treated urea), and four N rates (0, 80, 160 and 240 kg N ha-1 yr-1), replicated three times. Nitrogen sources promoted a positive effect (P<0.0001) on bulk density, forage mass, and in the grazing stratum during the wet season and the transition season, with increasing N rates in pastures. The leaf: stem ratio decreased linearly (P<0.0045) as increased N rates, and the higher ratio during the wet season and lower in the dry season of the year. For the rates of 80 kg N ha-1 yr-1, there was a significant difference (P=0.0042) between sources, with greater (P=0.0006) forage mass of 0–30 cm, post-grazing forage mass (P=0.0042) and forage volumetric density (P=0.0006), when utilized the conventional urea. The application of N, regardless of the source, provides an increase in forage mass and volumetric density in Xaraés grass pastures up to a dose of 240 kg N ha-1 yr-1, in the transition season and wet season.