Perspective: Impacts of dairy forage management on soil carbon change and net zero accounting

Authors: Gamble, Joshua; Alexander, Jonathan

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/3/2025
Publication Date: 4/29/2025
Citation: Gamble, J.D., Alexander, J.R. 2025. Perspective: Impacts of dairy forage management on soil carbon change and net zero accounting. Journal of Dairy Science. 108(5):4479-4484. https://doi.org/10.3168/jds.2024-25796.
DOI: https://doi.org/10.3168/jds.2024-25796

Interpretive Summary: The US Dairy Industry has pledged to achieve net zero greenhouse gas emissions (GHG) by 2050, but reliance on silage corn as a primary forage source undermines progress toward this goal. Previous research showed that soils managed for silage corn production are a significant source of carbon (C) emissions to atmosphere and result in considerable declines in soil C. These emissions from soil C change are not typically counted in the GHG or C-footprint of milk or other agricultural products. We argue that when soils under forage management are losing carbon, the associated emissions should be considered as part of the C-footprint of milk as some of lost soil C is potentially decades to centuries in age. Using an example dairy farm, we demonstrate that including emissions from soil C loss under silage corn management increases the C-footprint of milk nearly twofold. We suggest that this approach represents a more accurate estimate of the real emissions impact of production. The C balance of silage corn can be improved through greater return of manure C to the soil, but expanding the role of perennials and winter annual crops in forage rotations will also be required to reduce soil C loss.

Technical Abstract: The US Dairy Industry has pledged to achieve net-zero greenhouse gas emissions (GHG) by 2050, but reliance on corn silage as a primary forage source undermines progress toward this goal. Soils managed for silage corn production are a significant source of biogenic carbon (C) emissions to the atmosphere, with the potential for as much as 17.9 Mg CO2 ha-1 yr-1, indicating a considerable decline in soil C. However biogenic emissions from soil C change are not typically counted in C-footprints or life cycle inventories for agricultural products. We argue that when soils under forage management are below an equilibrium C balance, associated biogenic emissions should be considered as part of the C-footprint of milk because much of this soil C is decades to centuries in age. Moreover, these losses reduce soil fertility and compromise future productivity. Using an example dairy farm, we demonstrate that including emissions from soil C loss under silage corn management increases the C-footprint of milk nearly twofold. We suggest that this approach represents a more accurate estimate of the true emissions impact of production, and that gains in the GHG efficiency of milk have come, in part, at the expense of soil C. The C balance of silage corn can likely be improved with advanced manure management technologies and application strategies that return more manurial C to the soil while minimizing N and P loading. However, more extensive changes to forage cropping systems will be required if we are to balance soil C budgets and achieve net-zero emissions.