Date of this Version
McPhillips, L. J. 2021. Greenhouse gas emissions from two contrasting beef systems from birth to slaughter in eastern Nebraska. PhD Dissertation. University of Nebraska-Lincoln.
Over the last 15 years, the increase in land use for corn and soybean has come at the expense of acres of grasslands and perennial forages employed in conventional beef-production systems. Implementing alternative cow-calf production systems into existing cropping systems may be a solution for reduced land availability and reducing total greenhouse gas emissions (GHG). Therefore, GHG from a conventional (CONV) pasture-based cattle production system with cows wintered on corn residue and summer grazing of brome pasture were compared to partial-confinement system (ALT) with cows and calves in a drylot during the summer and grazing cover crops and corn residue over the fall and winter. Eddy covariance and pen chambers were used to measure emissions from grazing and confinement scenarios. Measured CH4 and modeled N2O emissions totaled 7.5 ± 0.3 and 7.4 ± 0.3 kg CO2e kg-1 HCW for CONV and ALT production, respectively. There was a measured uptake of 233 g C m-2 and 98 g C m-2 from brome pasture and cover crop, respectively. Accounting for CH4 and N2O emissions using global warming potential (GWP) of 23 and 298 resulted in a net sink of 0.7 ± 0.2 kg CO2e kg-1 HCW for CONV and a net source of 16.7 ± 1.5 kg CO2e kg-1 HCW for ALT. The same calculations using global warming potential (GWP) of 4 and 234 resulted in a net sink of 10.9 ± 1.0 kg CO2e kg-1 HCW for CONV and a net source of 7.1 ± 1.5 kg CO2e kg-1 HCW for ALT. Carbon sequestration from perennial grasslands in the CONV was enough to offset all emissions and biogenic CO2. Annual forage grazed in the ALT system offset 42 to 72% of systems emissions depending on GWP metric used. These net carbon results open new horizons to livestock carbon balance research and give evidence that grazing systems sequester carbon emissions from cattle and in some cases are a carbon sink.
Advisors: Galen E. Erickson and Andy Suyker