Long-term ecosystem carbon losses from silage maize-based forage cropping systems

Authors: Gamble, Joshua; Feyereisen, Gary; GRIFFIS, TIMOTHY - University Of Minnesota; Wente, Christopher - Chris; Baker, John

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2021
Publication Date: 8/15/2021
Citation: Gamble, J.D., Feyereisen, G.W., Griffis, T.J., Wente, C.D., Baker, J.M. 2021. Long-term ecosystem carbon losses from silage maize-based forage cropping systems. Agricultural and Forest Meteorology. 306. Article 108438. https://doi.org/10.1016/j.agrformet.2021.108438.
DOI: https://doi.org/10.1016/j.agrformet.2021.108438

Interpretive Summary: The US dairy industry is increasingly reliant on corn silage as a primary forage source, which may affect the long-term field carbon (C) balances. We show that long-term C losses were over threefold greater from silage corn-based forage cropping systems than from the predominant grain cropping system in the region, the soybean-corn rotation even when alfalfa, a perennial forage legume, was included in rotation and liquid dairy manure was field-applied. Since 1980, over 800,000 hectares of alfalfa have been converted to annual crops across the Upper Midwest US, and C export in harvested corn grain and silage have increased dramatically. These changes imply a substantial and unsustainable reduction in soil carbon on forage-cropped hectares in the Upper Midwest US. There is an acute need for management strategies that retain more plant-derived C in forage-cropped soils. Increasing the frequency of alfalfa or other perennial crops in the rotation, leaving more standing corn stover, and field-applying a greater fraction of the manure solids after solid-liquid separation could all help accomplish this goal to a degree. The findings of this research will be of interest to researchers and agency personnel with interest in dairy sustainability, greenhouse gas emissions, and forage cropping, and also to producers/producer groups with interest in forage cropping and maintaining/improving soil productivity, soil quality, and soil carbon sequestration in dairy systems.

Technical Abstract: The US dairy industry is increasingly reliant on maize silage as a primary forage source, which may affect the long-term C balance of fields in dairy forage production. Using 29 site-years of eddy covariance, plant, and manure measurements, we calculated long-term net ecosystem C balances (NECB) for two silage maize-based forage cropping systems and an annual soybean-maize rotation. We found that C losses were over threefold greater from continuous silage maize (-486 g C m-2 yr-1) than from the predominant grain cropping system in the region, the soybean-maize rotation (-133 g C m-2 yr-1). Including alfalfa in rotation reduced C losses by 23% relative to continuous silage maize, but net losses of C were still observed (-382 g C m-2 yr-1) . For every ton of crop residue C left in-field, net C balances increased by +0.9 Mg C ha-1. Application of liquid dairy manure improved C-balances, but rates were insufficient to offset C losses in respiration and crop harvest. Manure C application rates equivalent to 31% and 73% of the harvest C removal, or 135 and 602 g C m-2 yr-1, are required to maintain a net equilibrium C balance for alfalfa and silage maize, respectively. However, increasing manure rates to this degree (94% and 370% increases, respectively) would result in N and P surpluses and unacceptable rates of environmental loss. Greater reliance on maize silage has increased C losses from forage production, implying a substantial and unsustainable reduction in soil carbon on forage-cropped hectares in the Upper Midwestern US.