Canopy Height and Nitrogen Affect Herbage Accumulation, Nutritive Value, and Grazing Efficiency of ‘Mulato II’ Brachiariagrass

Abstract

Brachiaria sp. grasses are widely used in planted pastures in Brazil. ‘Mulato II’ is a productive Brachiaria hybrid (B. ruziziensis × B. decumbens × B. brizantha) with high nutritive value, but it has not been evaluated under continuous stocking in Brazil, despite this method being widely used by producers. The objectives of this research were to quantify the effects of three canopy heights (10, 25, and 40 cm), maintained by mimicking continuous stocking, and two N rates (50 and 250 kg ha–1 yr–1) on herbage accumulation (HA), grazing efficiency (GE), and nutritive value of Mulato II during two summer rainy seasons in Piracicaba, Brazil. The N rates were chosen so that canopy height effects could be evaluated under distinctly different grass growth rates. Grass HA increased linearly (8640 to 13,400 kg DM ha–1 yr–1), in vitro digestible organic matter (IVDOM) decreased linearly (652 to 586 g kg–1), and GE decreased (linear and quadratic; 65 to 44%) as canopy height increased. There were no height × N rate interactions for these responses. Mulato II was less productive (7940 vs. 13 380 kg ha–1 yr–1) and had lesser IVDOM (581 vs. 652 g kg–1) at the lower N rate. Thus, although GE and IVDOM were greatest for 10 cm, HA was 36% less for the 10‐ than the 40‐cm height, and despite greatest HA occurring at 40 cm, both GE and IVDOM were greater at shorter heights. These data suggest that ∼25‐cm canopy height is optimal for continuously stocked Mulato II.