Enteric Methane Emissions from Cattle in N-Fertilized Grass or Grass-Legume Pastures during Cool- and Warm-Seasons.

The objective of this project was to determine enteric CH₄ emissions, using the SF₆ tracer technique, from livestock grazing legume- or grass-based forage systems. The experiment was conducted at the University of Florida, North Florida Research and Education Center during the 2016 warm and cool seasons. Treatments were three forage production systems as follows: 1) N-fertilized bahiagrass (Paspalum notatum Flügge) pastures (113 kg N ha^-1) during the warm season, overseeded with a mixture (45 kg ha^-1 of each) of ‘FL 401’ cereal rye (Secale cereale L.) and ‘RAM’ oat (Avena sativa L.) during the cool season (BHF); 2) rhizoma peanut (Arachis glabrata Benth.)-bahiagrass pastures during the warm season, overseeded with the rye-oat mixture fertilized with 34 kg N ha^-1 plus a mixture of clovers (Trifolium sp.) during the cool season (BHR); and 3) unfertilized bahiagrass pastures during the warm season, overseeded with the rye-oat-clover mixture + 34 kg N ha^-1 during the cool-season (BH). No differences (P > 0.10) were observed in CH₄ emissions among treatments nor was there treatment × season interaction. During the cool-season, CH₄ emissions were 214, 180, and 184 g d^-1 for BH, BHF, and BHR, respectively. Enteric CH₄ emissions during the warm season averaged 243, 247 and 229 g d^-1 for BH, BHF, and BHR, respectively. No differences were observed (P > 0.10) in CH₄ emissions expressed per unit of area or per unit of forage intake among treatments or between seasons. Emissions of CH₄ per unit of average daily gain (ADG) did not differ (P > 0.10) among treatments, but they were greater in the warm vs. the cool season (P = 0.02). In conclusion, including legumes in cool- or warm-season pastures did not affect enteric CH₄ emissions by cattle, but CH₄ emissions per unit of ADG were less during the cool season.