Quantification of methane emissions from cattle farms, using the tracer gas dispersion method

Nathalia T Vechi,Johan Mellqvist,Charlotte Scheutz

doi:10.1016/j.agee.2022.107885

Nathalia T Vechi, Johan Mellqvist + Show 1 more

Open Access

https://doi.org/10.1016/j.agee.2022.107885

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Abstract

In Denmark, agriculture is the largest source of anthropogenic methane emissions (81%), mainly from cattle (dairy and beef) farms. Whole-farm methane emissions were quantified at nine Danish cattle farms, using the tracer gas dispersion method. Five to six measurement campaigns were carried out at each farm, covering a full year. Of the nine cattle farms, seven were home to dairy cows and two to beef cattle. The farms represented typical breeds, housing and management systems used in Denmark. Whole-farm methane emission rates ranged from 0.7 to 28 kg h−1, with the highest measurements seen at locations with the highest number of animals. Emissions tended to be higher from August to October, due to elevated temperatures and high amounts of stored manure during this period of the year. The average emission factor (EF) for dairy cow farms was 26 ± 8.5 g Livestock Unit (LU)−1 h−1, whereas it was 16 ± 4.1 LU−1 h−1 for beef cattle farms, i.e. 38% lower for the latter. The use of deep litter house management explained some of the differences found in the EFs for dairy cows. Methane emission rates estimated using IPCC models and national guidelines tended, on average for all farms and measurements, to be underestimated by 35% in comparison with the measured methane emissions, for all models and farms. The results suggest that future improvements to inventory models should focus on enteric methane emissions from beef cattle and manure methane emissions for both dairy cows and beef cattle, especially from deep litter management.

Highlights

Many countries have strengthened their greenhouse gas (GHG) reduction targets and are putting efforts into reducing associated emis sions with the goal of minimising climate change impacts
The results suggest that future improvements to inventory models should focus on enteric methane emissions from beef cattle and manure methane emissions for both dairy cows and beef cattle, espe cially from deep litter management
The lowest emission rates were recorded at beef cattle farm C8, which had only approximately 100 animals

Summary

Introduction

Many countries have strengthened their greenhouse gas (GHG) reduction targets and are putting efforts into reducing associated emis sions with the goal of minimising climate change impacts. Methane is the second most important emitted GHG and constitute 19% of the combined effective radiative forcing (relative to 1750) of the wellmixed GHGs (Forster et al, 2021). Due to the relatively short atmospheric lifetime of methane (IPCC, 2013), reducing its emissions will lead to cost-effective mitigation of climate change impacts in the short term (Johansson et al, 2008). In Denmark, 81% of all anthropo genic methane emissions come from agriculture, produced by both enteric fermentation and manure management (Nielsen et al, 2021). Of the methane emitted from cattle livestock, about 76% is due to enteric emissions from the ruminant digestive system and about 24% comes from degradation of animal manure, stored either under the animals’

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