Estimación de la huella de carbono de dos granjas lecheras portuguesas

Introduction: Dairy products constitute an important food source for human consumption; however, their production entails an environmental cost associated with the emission of greenhouse gases.
Many studies have been carried out to estimate the carbon footprint of dairy production. However, the analyzes conducted for standardized farms often do not represent the individual variability and complexity of each farm, which complicates the adoption of greenhouse gas mitigation measures for each particular case.
This study aimed to determine the carbon footprint of two distinct Portuguese dairy farms, one of conventional production and the other one of organic production.

Materials and Methods: We conducted a partial life cycle assessment of the two systems for the year 2022 using a “from cradle to farm gate” approach. The carbon footprint was calculated using the functional unit of 1 kg of energy-corrected milk (ECM, with 3.3% fat and 4.0% protein). System expansion was performed to consider the impact of meat.
The conventional farm is located in the district of Setúbal and has a herd size of 637 Holstein cows, producing 37.2 kg of ECM per cow per day. Manure undergoes solid-liquid separation with storage of the liquid fraction in a covered tank. Cows are fed with mostly imported feed as well as maize and grass silage produced on farm.
The organic farm is located in the district of Portalegre and has a dairy herd size of 771 mostly Jersey cows, producing 12.5 kg of ECM, as well as 553 beef cows. Animals spend most of their time on pasture. The period of the day when they are confined, they are fed with Total Mixed Ration made with forage produced on farm and supplemented with imported feed. The manure is stored in an open-air tank.
The Intergovernmental Panel on Climate Change (IPCC) guidelines were used to calculate gases associated with enteric fermentation, manure storage, and nitrogen application to soils. We estimated emissions associated with food imports, and the consumption of fossil fuels and electricity with emissions factors values from literature. The Rothamsted Carbon Model was used to estimate the amount of carbon sequestered in the soil of natural pastures of the organic farm.

Results: The results indicated a carbon footprint of 1.43 kg CO2-eq/kg ECM for the conventional farm and 2.82 kg CO2-eq/kg ECM for the organic farm. When sequestration was included, the carbon footprint of the organic farm was reduced to 2.06 kg CO2-eq/kg ECM.
For farm A imported feed accounted for most of the emissions (55% or 0.79 kg CO2-eq/kg ECM), followed by enteric methane (27% or 0.39 kg CO2-eq/kg ECM). For farm B the highest was enteric methane (58% or 1.63 kg CO2-eq/kg ECM), followed by feed import (28% or 0.79 kg CO2-eq/kg ECM).
We estimated 1.59 tons C/ha sequestered in pastures of the organic farm for the area of 800 hectares of pasture.

Discussion: Regarding conventional farm A, feed import constituted the largest source of emissions. Emissions from food production, effluent management and fertilizer production usually prevail in intensive systems. However, this value was higher than in literature, which can be due to lower crop production on farm and to the large import of feed such as soybean meal from South America.
Enteric methane was the largest source of emissions for organic farm B. Particularly for pasture-based systems, this is usually the case. Considering feed import, the value was also higher than found in literature for pasture-based systems. This could be explained by the necessity to import feed due to lack of quality and quantity of pasture, intensified by severe drought in 2022.
The high value of carbon sequestration per hectare obtained for the natural pastures in farm B was expected due to the regenerative agriculture practices with holistic grazing.
Increased productivity on the organic farm would reduce its carbon footprint since the unit in dairy systems is usually given per kilograms of milk. The carbon footprint could be decreased by reducing its herd size, as well as improving pasture quality, which would also reduce individual enteric methane emissions.

Conclusions: This study can constitute a starting point for the implementation of tailored mitigation measures on these two farms.
For the conventional farm, this study illustrated the importance of productivity, which can be achieved through genetic selection and improvement of nutrition, reproductive management and herd health. On the other hand, the results for the organic farm showed the impact of carbon sequestration on the farm footprint, thanks to regenerative agriculture practices which increase organic matter of the soil.
By exclusively estimating the carbon footprint and presenting the result in kilograms of milk produced, other environmental impacts were not reflected and would have certainly led to other results.

This work was supported by Fundação para a Ciência e a Tecnologia project UIDB/00276/2020 (CIISA) and LA/P/0059/2020 (AL4AnimalS).

  • vetoquinol
  • analítica veterinaria
  • delaval
  • innogando
  • Secure Cattle
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  • DML Datamars Livestock
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