Caracterização agronômica e químico-bromatológica da Brachiaria híbrida spp. sob adubação nitrogenada e potássica

Abstract

Under the hypothesis that new options of forage grass should be studied with relationship to the behavior of the determinant variables so much of the production, as of the quality of the forage, it were evaluated the morfogenetic, structural, and of the dry mass accumulation characteristics, besides the accumulation and the morphologic and chemical compositions of the forage of Brachiaria hybrid spp. (Brachiaria decumbens x Brachiaria ruziziensis) fertilized with nitrogen and potassium, and managed under light interception criterion, during the seasons. The treatments consisted of a control (without fertilizer) and of three doses of nitrogen and potassium (120, 240 and 360 kg/ha/year of N and K2O), done during the seasons. The completely randomized block design was used with four treatments and five replications, under split-plot arrangement, with doses allocated to the plots and seasons, to the subplots. The morphogenetic, structural, and of the dry mass accumulation variables, besides accumulation and morphologic and chemical compositions of the forage of Brachiaria hybrid were influenced, in an united way, for the nitrogen and potassium fertilization and for the environmental conditions of the seasons. The phyllochron and leaf elongation rate responded quadratically, while the stem elongation rate of Brachiaria hybrid responded quadratically during the summer one and a linear increase during the second summer in response to nitrogen and potassium.The densities and percentages of birth and mortality tiller rates and the specific leaf area increased linearly with the nitrogen and potassium fertilization, determining similar effect in the leaf area index during the spring and summer. The leaves accumulation rates were the basic determinant of the linear behavior the forage accumulation rates, while the linear increase of the senescent rates determined the quadratic behavior of the liquid forage and leaves accumulation rates during the summer, in response to the nitrogen and potassium fertilization. The nitrogen and potassium fertilization increased the crude protein content and reduced levels of neutral detergent fiber and acid detergent and lignin of forage. The Brachiaria hybrid constitute as forage grass of high potential of forage production during the summer, with high seasonal production in relation to the autumn/winter, and it presents linear increase in the forage accumulation during the summer, and improvement in the chemical composition during the spring and summer, in response to nitrogen and potassium fertilization.