Quantifying methane and ammonia emissions from beef cattle finishing systems under sorghum and corn diets

The rising demand for animal products globally underscores the need to diversify feed grain inclusion in beef finishing systems while reducing the environmental footprint of animal agriculture. The primary objective of this study was to quantify and compare the effects of grain sorghum- versus corn-based finishing diets on methane (CH 4 ) and ammonia (NH 3 ) emissions from different groups of cattle in a feedlot. The study was conducted at the Kansas State University Southeast Research-Extension Center in Mound Valley, Kansas, USA for approximately six months. The cattle in this study consisted of black-hided, crossbred yearling steers. We simultaneously monitored CH 4 and NH 3 emissions using open-path dual-comb spectroscopy (DCS) from five paired cohorts of steers, with one fed dry-rolled corn diet and the other fed a ground sorghum diet. Line-averaged gas concentrations, obtained using DCS along with wind statistics and atmosphere stability parameters, were used in an inverse dispersion model to determine CH 4 and NH 3 fluxes. The use of a single DCS system eliminates potential biases occurring when using multiple instruments to measure concentration differences. The prevailing wind direction at the site and the east-west layout of the pens maximized data retention at the site. However, our touchdown analysis demonstrated that screening flux data using solely wind direction is insufficient to prevent contamination from other neighboring source areas in the feedlot. The median hourly NH 3 fluxes in this study ranged from 14.4 to 212.3 µg m –2 day –1 for NH 3 and from 144.9 to 513.4 g CH 4 head –1 day –1 for CH 4 , respectively. NH 3 fluxes showed a pronounced diurnal variation relative to CH 4 fluxes. Overall, the sorghum diet resulted in a 12% reduction (95 CI: 1% to 21%) in CH 4 fluxes relative to the corn diet. Median hourly NH₃ fluxes were typically higher under the sorghum diet, but the statistical analysis did not confirm NH 3 emission differences between diets.