Abstract

Understanding the action of the nitrogen (N) in grasses can aid in pasture management and increase the efficiency of this nutrient. The objective of this study was to determine the influence of N rates and of the available N from the previous crop on Brachiaria ruziziensis cv. Comum. The experiment was conducted in a greenhouse. The treatments were arranged in a 2×4 factorial design and were distributed according to a fully randomized block design with four replications. Two N rates (0 and 15 mg dm^-3) were applied at grass planting and four N rates were applied as topdressing after the first cutting (0, 15, 30 and 45 mg dm^-3). The grass was cut twice above-ground. The comparison between N rates applied at planting was made using F test, and the degrees of freedom of the N rates applied as topdressing were broken down into orthogonal polynomials. The N rate of 15 mg dm^-3 applied at planting the ruzi grass promoted increases in the numbers of leaves and shoot dry matter production. During the second growth, N rates (15, 30 and 45 mg dm^-3) applied as topdressing increased the number of leaves and the shoot dry matter production. The available N from the previous crop (soybean) was sufficient for the initial tillering of the ruzi grass. This study showed that the correct management of N fertilization is necessary for ruzi grass when grown after a previous crop (soybean).

Key words: Available nitrogen, forage plants, management of nitrogen, residual nitrogen.