Nutritional Quality of Brachiaria Under Two Contrasting CO2 Environment Conditions.

Beef cattle production in Brazil is grounded in Cerrado land grazing Brachiaria species and little data exists on potential changes in chemical composition and nutritional quality of tropical forages for livestock production under the scenario of CO2 enriched atmosphere. The aim of this work was to determine the effects of elevated CO2 concentrations upon the total biomass production and fibre quality of Brachiaria decumbens. FACE facility was established in twelve 10-m-diameter octagonal rings: six rings being the control treatment, were left under untreated conditions (current atmosphere), whereas other six rings have been treated with pure CO2 to achieve the concentration of 200 ppm above ambient concentration. Within each ring, two plots have been established with Brachiaria decumbens and after a cut for standardization; forage availability was estimated every 28 days throughout 2012 and 2013. Samples of 0.25m2 were collected from each plot, through cutting with scissors the grazing portion of the stand (at 20 cm height). Collected samples have been evaluated for determining the biomass availability, plant fractions, chemical determinations and fiber degradability. Data was statistically analysed by GLM (model = co2 season year plot block). Elemental C, N and S composition (%) were not altered by enriched CO2 atmosphere. Biomass available (0.29 vs 0.25 Kg DM / m2, (SE 0.01)) and ADF content (326 vs 321 g/Kg DM (SE 1.9)) for enriched vs ambient respectively were statistically affected by CO2 conditions. The in vitro organic matter degradability (DMO) tended to be lower (P = 0.09) for the enriched conditions (599 vs 609 (SE 4.4) g/Kg DM), while there were no differences (P = 0.229) for the fibre degradability (42 ± 10.1 g/Kg). The increase in pasture biomass available, in ADF content and reduction on DMO with CO2 enrichment atmosphere suggest studies to improve ruminal availability of nutrients for the sustainability of the ruminant production whilst ambient CO2 concentration maintain its increasing.