Conclusions
Although the value of comparison among milk C-footprints resulting from studies analysing other production systems and countries is very limited since methodologies and assumptions are often very different, the global warming potential resulting from the production of 1 kg of milk in the Basque Country (northern Spain) was within the range of existing studies. This study showed that cow diet choice (source and origin) is an important management factor controlling C-footprint of milk and may have a strong influence, sometimes positive, on competing human resources as food. Confinement dairy farms in locations with land limitation import large amounts of nutrients via feed and not so much through mineral fertiliser. Therefore, it becomes critical that the nutrients that do not result in animal product (manure) are most efficiently recycled in the soil–plant system. By doing so, farmers are likely to improve their net margins and lower their milk C-footprint. Although a comprehensive uncertainty analysis is beyond the scope of this study, it can be speculated through the different examples used in this study that the predictions for GHG emissions from milk production are still subject to large uncertainties driven by methodology choice and input data availability. Insufficient information on land management history is for example the main limitation for improving the estimation of soil C dynamics from commercial dairy farms. Therefore, until this limitation is overcome, milk C footprint studies will not be able to fully account for the potential role of soil grasslands as C sinks.
Conclusions
Although the value of comparison among milk C-footprints resulting from studies analysing other production systems and countries is very limited since methodologies and assumptions are often very different, the global warming potential resulting from the production of 1 kg of milk in the Basque Country (northern Spain) was within the range of existing studies. This study showed that cow diet choice (source and origin) is an important management factor controlling C-footprint of milk and may have a strong influence, sometimes positive, on competing human resources as food. Confinement dairy farms in locations with land limitation import large amounts of nutrients via feed and not so much through mineral fertiliser. Therefore, it becomes critical that the nutrients that do not result in animal product (manure) are most efficiently recycled in the soil–plant system. By doing so, farmers are likely to improve their net margins and lower their milk C-footprint. Although a comprehensive uncertainty analysis is beyond the scope of this study, it can be speculated through the different examples used in this study that the predictions for GHG emissions from milk production are still subject to large uncertainties driven by methodology choice and input data availability. Insufficient information on land management history is for example the main limitation for improving the estimation of soil C dynamics from commercial dairy farms. Therefore, until this limitation is overcome, milk C footprint studies will not be able to fully account for the potential role of soil grasslands as C sinks.
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