ABOVEGROUND AND TOTAL ROOT BIOMASS COMPONENTS OF Brachiaria PASTURES IN DIFFERENT AGES AFTER RENOVATION AS A PRODUCTION INDICATOR UNDER SAVANNA VEGETATION

Abstract

This study aimed to evaluate the production components of aboveground and total root stock biomass of Brachiaria pastures of different ages after renovation. Three B.brizantha pastures, with one, seven, and nine years after renovation through the Barreirão system, and one B. decumbens pasture twenty years after traditional renovation were evaluated. The areas were located at Goiânia, Brazil (16º35'12";S, 49º21'14";W, 730 m). The one year after renovation pasture showed the highest productivity, 197% higher than the twenty year after renovation pasture. With increasing pasture renovation age, there was a production and regrowth rate decrease due to the degradation process. This aspect may be observed in the root system development, since the total root productivity to 100 cm depth was reduced as pasture age increased, with 9.14 Mg ha-1, 4.87 Mg ha-1, and 2.90 Mg ha-1 for pastures of seven, nine, and twenty years after renovation, respectively. The one year pasture did not show appreciable root contribution. The Brachiaria regrowth pasture was found to be dependent on system N availability; hence, the litter production showed to be a good pasture degradation indicator. The N stocks down to 100 cm depth were of 7.54 Mg ha-1, 8.70 Mg ha-1, and 9.47 Mg ha-1, in the pastures with one, seven, and twenty years, respectively. These values were much lower than those in the nine year after renovation pasture (14.2 Mg ha-1).

KEY-WORDS: Brachiaria; pastures; roots; litter.