Herbage Accumulation and Grazing Efficiency of Mulato II Brachiariagrass Under Contrasting Growth Rates and Canopy Height Maintained By Continuous Stocking.

Grazed pastures are the backbone of the Brazilian livestock industry and grasses of the genus Brachiaria are some of most used tropical forages in the country. Mulato II brachiariagrass (Convert HD 364^®), a new Brachiaria hybrid, was released as an option for a broad range of environmental conditions. There is no scientific information, however, on specific management practices for Mulato II under continuous stocking. The aim of this research was to describe and explain herbage accumulation and grazing efficiency responses of hybrid Convert HD 364 (cv. Mulato II) in response to growth rate and canopy height under continuous stocking. A field study was carried out in Piracicaba, SP, from December 2012 to April 2013, corresponding to the summer rainy season. A RCB design was used, with a 3 x 2 factorial arrangement, corresponding to three steady-state canopy heights (10, 25 and 40 cm) maintained by continuous stocking and two growth rates (“low” and “high”) imposed by two N rates (50 and 250 kg N ha^-1 yr^-1), with three replications. Herbage accumulation was calculated based on the results of the evaluations of the morphogenetic and structural characteristics of marked tillers (30 per paddock), which were replaced every 28-d.  Grazing efficiency was calculated as the percentage of total forage mass that was harvested during 28-d periods, discounting forage losses (by grazing and senescence). Data were analyzed using PROC MIXED of SAS, and treatment means compared by Tukey-test at the 5% level of probability. Herbage accumulation and grazing efficiency were affected by height (P=0.00891 and P=0.0002, respectively) and growth rate (P=0.00186 and P=0.0352, respectively). Taller canopies (40-cm) accumulated more forage  (12650 kg DM ha^-1) than short canopies (10-cm) (9190 kg DM ha^-1), although with lower grazing efficiency (40.3 % for 40-cm compared to 61.2 % for 10-cm). The 25-cm height resulted in intermediate herbage accumulation (11310 kg DM ha^-1), and greater grazing efficiency (53.1%) than 40-cm canopies.  Herbage accumulation increased with increased growth rate (8130 to 13790 kg DM ha^-1), but grazing efficiency was lower under higher (46.2%) than lower (55.7%) growth rates. Intermediate levels of grazing efficiency and herbage accumulation suggest that the 25-cm canopy height is best for Mulato II under continuous stocking, and that herbage accumulation and grazing efficiency are inversely related.