Effect of feeding strategies and cropping systems on greenhouse gas emission from Wisconsin certified organic dairy farms

Abstract

Organic agriculture continues to expand in the United States, both in total hectares and market share. However, management practices used by dairy organic producers, and their resulting environmental impacts, vary across farms. This study used a partial life cycle assessment approach to estimate the effect of different feeding strategies and associated crop production on greenhouse gas emissions (GHG) from Wisconsin certified organic dairy farms. Field and livestock-driven emissions were calculated using 2 data sets. One was a 20-yr data set from the Wisconsin Integrated Cropping System Trial documenting management inputs, crop and pasture yields, and soil characteristics, used to estimate field-level emissions from land associated with feed production (row crop and pasture), including NO and soil carbon sequestration. The other was a data set summarizing organic farm management in Wisconsin, which was used to estimate replacement heifer emission (CO equivalents), enteric methane (CH), and manure management (NO and CH). Three combinations of corn grain (CG) and soybean (SB) as concentrate (all corn = 100% CG; baseline = 75% CG + 25% SB; half corn = 50% CG + 50% SB) were assigned to each of 4 representative management strategies as determined by survey data. Overall, GHG emissions associated with crop production was 1,297 ± 136 kg of CO equivalents/t of ECM without accounting for soil carbon changes (ΔSC), and GHG emission with ΔSC was 1,457 ± 111 kg of CO equivalents/t of ECM, with greater reliance on pasture resulting in less ΔSC. Higher levels of milk production were a major driver associated with reduction in GHG emission per metric tonne of ECM. Emissions per metric tonne of ECM increased with increasing proportion of SB in the ration; however, including SB in the crop rotation decreased NO emission per metric tonne of ECM from cropland due to lower applications of organically approved N fertility inputs. More SB at the expense of CG in the ration reduced enteric CH emission per metric tonne of ECM (because of greater dietary fat content) but increased NO emission per metric tonne of ECM from manure (because of greater N content). An increased reliance on pasture for feed at the expense of grain resulted in decreased in milk production, subsequently leading to substantially higher emissions per metric tonne of ECM.

Life cycle assessment of carbon dioxide removal technologies: a critical review

“…However, some SCS studies showed a loss of soil carbon instead of SCS for a variety of cropping systems (e.g. 130,138,142 ). Further, most studies reported total carbon emissions for the entire product system, but not negative carbon emissions due to SCS as such.…”

“…123,124,135 ) or economic value (e.g. 117,130 ). For cropping systems, allocation was usually not required with gate-to-gate system boundaries, since the only function was to deliver the feedstock to the farm gate.…”

Symposium review: Comparisons of feed and milk nitrogen efficiency and carbon emissions in organic versus conventional dairy production systems

“…However, research on nutrition, genetics, and whole-farm systems is needed to guide farmers' decisions on how to best feed and breed to optimize forage DMI and milk production while reducing the environmental impact of organic dairies. Liang et al (2017), using the integrated farm systems model (Rotz, 2013), showed that greenhouse gas emissions per tonne of ECM, with or without accounting for soil carbon change, were greatest in organic dairy farms belonging to cluster 2 followed by clusters 4, 1, and 3. Their whole-farm modeling simulations indicated that more greenhouse gas was emitted into the environment the longer the cows had access to pasture during the grazing season (Liang et al, 2017).…”

“…Liang et al (2017), using the integrated farm systems model (Rotz, 2013), showed that greenhouse gas emissions per tonne of ECM, with or without accounting for soil carbon change, were greatest in organic dairy farms belonging to cluster 2 followed by clusters 4, 1, and 3. Their whole-farm modeling simulations indicated that more greenhouse gas was emitted into the environment the longer the cows had access to pasture during the grazing season (Liang et al, 2017). Grass-fed organic dairies use nutritional and management strategies that resemble those adopted by farms in cluster 2 (Hardie et al, 2014;Liang et al, 2017) except the lack of concentrate.…”

“…Their whole-farm modeling simulations indicated that more greenhouse gas was emitted into the environment the longer the cows had access to pasture during the grazing season (Liang et al, 2017). Grass-fed organic dairies use nutritional and management strategies that resemble those adopted by farms in cluster 2 (Hardie et al, 2014;Liang et al, 2017) except the lack of concentrate. Thus, it is conceivable that whole-farm greenhouse gas emissions could be greater in grass-fed dairies than in farms from cluster 2.…”