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.

Canopy height and N affect herbage accumulation and the relative contribution of leaf categories to photosynthesis of grazed brachiariagrass pastures

“…Canopies kept at shorter heights often have smaller LAI compared with taller canopies (Silva et al., ). Barker et al.…”

“…brizantha × U. decumbens × U. ruziziensis )] is a Brachiaria hybrid, marketed in Brazil as Convert HD 364 (Dow AgroSciences, São Paulo, Brazil). This hybrid is an option for diversification in pasture‐based systems due to its high herbage accumulation (HA) and nutritive value (Pequeno et al., ; Silva et al., ).…”

Carbon assimilation, herbage accumulation, nutritive value, and grazing efficiency of Mulato II brachiariagrass under continuous stocking

“…Thus, the combination of increased LAI and leaf CER due to N fertilization contributed to increase the canopy CER, which resulted in greater HA. In fact, in a companion study the total annual HA of Mulato II was increased by 69% with 250 compared with 50 kg N ha -1 (SILVA et al, 2016). …”

“…In addition, there is an increased interest of pasture areas for other agricultural activities considered more profitable, such as sugar-cane and grain crops (ALKIMIM;SPAROVEK;CLARKE, 2015). If well managed, however, the actual pasture area could support a much greater number of animals, contribute to carbon sequestration, and help to mitigate greenhouse gas emissions (SILVA et al, 2016).…”

“…Net total HAR, however, was also increased indicating that the increase in senescence was not great enough to compromise the potential of HA in taller canopies. The combination of high senescence rates and herbage mass, however, can contribute to lesser grazing efficiency (SILVA et al, 2016). Additionally, increased senescence rates in taller canopies may be detrimental to the canopy structure in the long term.…”