Eficiência nutricional e aproveitamento do nitrogênio pelo capim-marandu de pastagem em estágio moderado de degradação sob doses e fontes de nitrogênio

Abstract

This study was accomplished under field conditions, to evaluate the use and efficiency of nitrogen uptake, through various indexes, in pasture of Brachiaria brizantha. The experiment was conduced at the Model Farm of the Goiás State University in a distrophic Dark Red Latosol, from 2003 July to 2006 March. The experimental design was randon blocks, with three replicates. The treatments were placed in parcels characterized by a 2x4 factorial, with two sources of N (ammonium sulfate and urea) and four doses of N (0, 100, 200 and 300 kg/ha/year). In sub - parcel, the treatments were represented per years (2004, 2005 and 2006) refering to time of pasture recovery. The use of nitrogen was divided in three times, after each cut evaluation of the forage pasture. Three cuts were made per year, evaluating dry mass and N accumulation in the tissue. Nitrogen Utilization Efficiency, Recovery from the N Applied, Agronomic Efficiency from the N Applied, Physiological or Biological Efficiency indexes were evaluated. The results showed that EUN increased, while RNA, EA and EF reduced with the increase in the N doses applied. In all cases, the indexes were influenced by the years of recovery the herbage, and not by the sources of N.