Greenhouse gas and ammonia emissions from two floor types of naturally ventilated dairy barns in Denmark

Introduction<br/>Greenhouse gas (GHG) emissions from agriculture, particularly from livestock production, contribute significantly to global climate change. Dairy farming is a major source of methane (CH₄) and nitrous oxide (N₂O) emissions. In livestock systems, naturally ventilated dairy barns present unique measurement complexities due to spatial gas distribution and the inability to directly measure the ventilation rate, leading to higher uncertainty compared to mechanically ventilated barns. Accurate quantification of emissions from these systems is critical for establishing accurate emission values as well as developing mitigation strategies aligned with climate targets. This study focuses on GHG and ammonia (NH₃) emissions from naturally ventilated Danish dairy cubicle barns with either slatted floors above continuous slurry channel systems, where slurry is frequently circulated by pumping (frequently stirred slurry channels) or drained solid floors with frequent scraping of the floors and limited slurry stored inside the barn (drained solid floor). The barns were housing 200 – 300 dairy cattle. We will present preliminary results from an ongoing measurement campaign ending October 2025.<br/>Methodology<br/>Emissions are determined with the tracer gas ratio method using carbon dioxide (CO₂) produced by animals and manure as a natural tracer gas. CO2, CH4, N2O, and NH3 concentrations are measured with Cavity Ring-Down Spectroscopy (Picarro G2509). The air is sampled via a sampling line consisting of a partly heated and insulated FEP or PTFE tube with multiple sampling points. The sampling line is mounted in the middle of the barn along the length of the barn at circa 4 m above ground. Thus, a representative air sample with an average barn air concentration is taken. Measured are four barns with frequently stirred slurry channels and four barns with drained solid floor. The barns are measured six times over the course of a year for at least 72 hours. Additionally, the feed and the slurry are analysed for each measurement campaign.<br/>Results and discussion<br/>The results presented in this abstract are preliminary and incomplete. Barns equipped with frequently stirred slurry channels have on average, emission values of 0.38 kg CH4 livestock unit-1 (LU, 500 kg live weight) d-1 and 35 g NH3 LU-1 d-1. Conversely, the barns with drained solid floor exhibited 0.30 kg CH4 LU-1 d-1 and 30 g NH3 LU-1 d-1. This indicates that the CH4 emissions are ca. 30% and NH3 emissions are about 20% higher per LU for cattle housed in barns with frequently stirred slurry channels. This is attributable to the longer storage period of slurry and larger soiled surface in barns with frequently stirred slurry channels in comparison to that of a drained solid floor, where manure is removed on a daily basis to an outside storage. A positive correlation between the ambient temperature and the emission of CH4 and NH3 was observed. The preliminary findings align with current literature data: however, a significant portion of the measurements are still ongoing (23 out of 48 campaigns are completed). Further, the data have not yet been corrected for dry matter and nitrogen intake, slurry composition, and animal space. Additionally, some barns housed calves, heifers, dry cows, and lactating cows, whereas in other barns only cows were present. In barns with not only cows present, the ratio in LU of cows to calves and heifers was up to 1:0.44. This variation complicates the comparison of data, particularly in the absence of standardisation of dry matter and crude protein intake. While the trend in the emission data is anticipated to be consistent, the relative difference between the two systems may persist until the project’s conclusion in October 2025, as the absolute emission values are subject to change.<br/>Conclusion<br/>As this is an ongoing study with a scheduled conclusion in October 2025, the final results are not yet available but will be presented at the conference. Consequently, it is premature to draw any conclusions at this juncture.<br/>Acknowledgements<br/>The project is funded by the Danish Agricultural Agency, 33010-NIFA-21-766. The help of the technical staff at Campus Aarhus University Viborg is greatly acknowledged.<br/>