Nitrogen is the mineral element that plants most require. Its deficiency quickly inhibits plant growth. Excessive nitrogen fertilization raises the cost of biomass production. Therefore, there is a need to find the appropriate dose of nitrogen fertilizer that provides greater efficiency in dry matter production. The objective of this study was to evaluate the effects of nitrogen and phosphate fertilizers on the chemical composition of the biomass of elephant-grass for energy use. A randomized-blocks experimental design in a split-plot arrangement was adopted. Three elephant-grass genotypes were evaluated (Guaçu/IZ.2, Cameroon-Piracicaba, and Capim Cana D’África) with five levels of nitrogen fertilization (0, 250, 500, 1,000 and 2,000 kg ha–1), as urea, and four levels of phosphate fertilization (50, 100, 200 and 400 kg ha–1), as single superphosphate. Results showed that the chemical composition, determined by the neutral detergent fiber (NDF), acid detergent fiber (ADF), cellulose (CEL), and lignin (LIG), contents displayed values that qualified the researched genotypes for energy use. Nitrogen applications had a quadratic effect on NDF and LIG contents in genotype Guaçu/IZ.2. A maximum dose of nitrogen fertilizer that will provide greater efficiency in the use of nitrogen for energy use varies among elephant-grass genotypes.
Key words: acid detergent fiber, cellulose, lignin, neutral detergent fiber.