Effect of Season and Nitrogen Fertilization on the Agronomic Traits and Efficiency of Piatã Grass in Brazilian Savanna

The aim of the present study was to evaluate the agronomic traits in the pre- and post-grazing and the nitrogen use efficiency of Piatã grass that was subjected to nitrogen fertilization throughout the seasons of the year. The experiment was performed in a randomized block design with four treatments (0, 150, 300, and 450 kg ha −1 N). Grazing was performed with sheep when the forage canopy reached 95% light interception up to 20 cm height of post-grazing. The pre-grazing forage mass of the Piatã grass showed a behavior ( p < 0.05) linear to nitrogen fertilization, with higher and lower values in spring and winter, respectively. The post-grazing forage mass responded linearly ( p < 0.05) to nitrogen fertilization, with an increase of 43.12% for the dose of 450 kg ha −1 N in relation to pastures without nitrogen fertilization. When the non-fertilized pasture was compared with the highest nitrogen dose, a reduction of 21.79% dead tissue was observed in the post-grazing forage mass. The highest nitrogen use efficiency was obtained with the dose of 450 kg ha −1 N. The forage mass production of the Piatã grass in the pre- and post-grazing conditions are positively influenced by nitrogen fertilization and the seasons of the year, with lower values in winter.