Carbon dioxide fluxes and carbon balance of an agricultural grassland in southern Finland

Abstract. A significant proportion of the global carbon emissions to the atmosphere originates from agriculture. Therefore, continuous long-term monitoring of CO₂ fluxes is essential to understand the carbon dynamics and balances of different agricultural sites. Here we present results from a new eddy covariance flux measurement site located in southern Finland. We measured CO₂ and H₂O fluxes at this agricultural grassland site for two years from May 2018 to May 2020. Especially the first summer experienced prolonged dry periods, which affected the CO₂ fluxes, and substantially larger fluxes were observed in the second summer. During the dry summer, leaf area index (LAI) was notably lower than in the second summer. Water use efficiency increased with LAI in a similar manner in both years, but photosynthetic capacity per leaf area was lower during the dry summer. The annual carbon balance was calculated based on the CO₂ fluxes and management measures, which included input of carbon as organic fertilisers and output as yield. The carbon balance of the field was −50 ± 68 g C m⁻² yr⁻¹ and −118 ± 24 g C m⁻² yr⁻¹ during the first and second study year, respectively. We estimated that on average the grassland exceeded the global 4 per 1000 goal to increase the soil carbon content.