Effect of different nitrogen fertilizers on nitrogen efficiency use in Nellore bulls grazing on Marandu palisade grass

Abstract

We evaluated the effects of different sources of nitrogen (N) applied to pastures of Urochloa brizantha cv. Marandu during the rainy season on the efficiency of N use in plants and animals. Continuous grazing with variable stocking rates was employed to maintain 25 cm pasture height, corresponding to 95% light interception. The experimental design consisted of randomized blocks with four treatments and three replications (paddocks per treatment). The applied N sources were urea, ammonium sulfate, and ammonium nitrate, at a respective dosage of 150 kg N per ha, in three treatments, in addition to a control treatment without N fertilization. N recovery by plants differed between fertilizers (p = 0.047) and was highest in the ammonium sulfate treatment. The proportion of retained N was higher in animals kept on fertilized pastures (p < 0.01). Different sources of N in pasture system, or its non-use, affected the efficiency of N use by animals, and ammonium sulfate and ammonium nitrate were more efficient with respect to the N balance.