Abstract
The objective of this study was to assess the agronomic and nutritional responses of the elephant grass cultivar Carajas when subjected to fertilization with protected and conventional urea. A randomized block design with 4x2+1 factorial arrangement was adopted. The treatments consisted of four doses (100, 200, 400, and 800 kg N ha(-1)), two nitrogen sources (conventional and protected urea), and one additional treatment without fertilization. The experiment was carried out from October 2015 to March 2016, in a semi-arid region with a dystrophic yellow latosol type soil. The application of conventional urea was done with each of the multiple cuts performed per year, whereas the protected urea was applied in a single dose. Total senescence rate (TSR), leaf and stem elongation, height, tiller density, total forage biomass, green leaf and stem biomass, and dry matter all increased with increasing N doses. However, the phyllochron, live material/dead material ratio, and agronomic efficiency all decreased with N increasing dose. Plants fertilized with protected urea presented greater TSR and phyllochron. Mineral matter content was higher in plants fertilized with conventional urea. Neutral detergent fiber content was maximized at a dose of 437.63 kg N ha(-1). The protected urea resulted in a higher value of leaf/stem ratio at the 400 kg N ha(-1) dose, whereas ether extract and crude protein at the 800 kg N ha(-1). With application of conventional urea, the highest crude protein value occurred at a dose of 100 kg N ha(-1). The morphogenesis, structure, production, and chemical composition of elephant grass 'Carajas' were all positively influenced when nitrogen doses were increased, with the recommended optimal dose for use being 400 kg N ha(-1) for both sources. The use of protected urea is recommended because of its slow release and need for only a single application.