Características morfogênicas, estruturais, produção e composição química do capim-elefante cv. carajás adubado com ureia convencional e protegida

Abstract

The objective in this study was to evaluate the morphogenic, structural and production characteristics, and chemical composition of Elephant-grass cultivar Carajás, fertilized with conventional and polymer-protected urea. The experimental design adopted was randomized blocks with factorial arrangement 5x2, where the treatments consisted of five nitrogen doses (0, 100, 200, 400 and 800 kg ha-1 year-1) and two nitrogen sources (conventional and polymer-protected urea). The leaf elongation rate (LER), leaf appearing rate (LAR), stem elongation rate (SER), phyllochron, total senescence rate (TSR), height, population density of tillers per clump (PDTC), leaf/stem ratio (L/S), live material/dead material ratio (LM/DM), total forage biomass (TFB), green leaf biomass (GLB); green stem biomass (GSB), dry matter content (DM), mineral matter (MM), crude protein (CP), ether extract (EE), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were evaluated. LAR, LER, SER, TSR, height, PDTC, TFB, GLB, GSB and DM presented increase of 0.0002 leaves/day, 0.0041 cm•tiller-1•day-1, 0,0004 cm•tiller-1•day-1; 0,0007 cm•tiller-1•day-1; 0,0148 cm; 0,0274 tiller/linear meter; 0,0223 ton•DM•ha-1•year-1; 0,0094 ton•DM•ha-1•year-1; 0,1214 ton•DM•ha-1•year-1 e 0,0017%, respectively for each nitrogen unit applied. Phyllochron and LM/DM presented decrease of 0,0024 days and 0,0026 respectively, for each kilogram of nitrogen applied. For phyllochron and TSR the plants fertilized with protected urea presented higher values than plants fertilized with conventional urea, whereas for MM the plants fertilized with conventional urea presented higher contents than those fertilized with protected urea. For the L/S ratio only at 400 kg N•ha-1•year-1, there was difference between the sources, where protected urea presented higher L/S ratio than conventional urea. The NDF presented maximum value at the dose 437.63 kg N•ha-1•year-1. The ADF showed no effect on the interaction, sources or doses of nitrogen. The EE showed difference between the sources only for the dose 800 kg of N•ha-1•year-1, where protected urea presented a higher content than conventional urea. For PB only at doses 100 and 800 kg of N•ha-1•year-1 there was difference between the sources, where at the dose 100 kg of N•ha-1•year-1 the conventional urea was superior to the protected urea and at the dose 800 kg of N•ha-1•year-1 the protected urea presented higher CP content. The morphogenic, structural and production characteristics and chemical composition of elephant grass cv. Carajás are positively influenced by the increase of the nitrogen dose. The use of protected urea is recommended because of it slow release and single dose application.