Case Study: Assessment of greenhouse gas intensities on exemplary small and mid-sized US dairy farms

Abstract

Objective

Our objective was to estimate greenhouse gas (GHG) intensities for 4 dairy farms representing the Northeast, Great Lakes, West, and Southeast US regions using the Farmers Assuring Responsible Management: Environmental Stewardship (FARM ES) life-cycle analysis model.

Materials and Methods

Four herds with <1,000 lactating cows, on farms selected as excellent environmental stewards, were assessed, with mean (±SD) production of 10,782 ± 2,037 kg/yr fat- and protein-corrected milk (FPCM). Data from 2021 were gathered from management software, interviews, and on-farm evaluations. Soil OM data for ≥7 yr were available on 3 farms. Emissions intensity was quantified as net CO₂ equivalents (CO₂e) emitted per unit of FPCM sold.

Results and Discussion

Mean (±SD) GHG emissions intensity was 0.97 ± 0.16 kg of CO₂e/kg of FPCM. In terms of point sources, FARM ES attributed 42 ± 6% of the farms’ emissions to enteric methane and 28 ± 9% to manure emissions. The remaining emissions were associated with feed production and energy use. Two farms that used manure separation had an average emissions intensity 0.20 kg of CO₂e/kg of FPCM less than farms that did not. Average annual soil carbon sequestration rates ranged from −0.82 to 3.52 Mg of carbon/ha, decreasing mean net GHG emissions intensity by 18% on these farms (0.81 vs. 0.99 kg of CO₂e/kg of FPCM).

Implications and Applications

Management practices have wide-ranging implications for dairy farm emissions intensities, and quantifying soil carbon sequestration is key for estimating net GHG emissions for a dairy farm.