GHG balance, its seasonality and response to soil type and management of northern agricultural grasslands: Eddy-covariance flux measurements from three adjacent fields in Finland

Understanding how managed grasslands respond to climate and management regimes across global pedoclimatic zones is crucial to combating climate change. In this study, we used the eddy covariance method to continuously measure GHG fluxes from January through December 2022 at three boreal grassland sites in eastern Finland: Anttila on mineral soil, and Särkisuo and Pappilansuo on drained peat soils. Our results highlight significant seasonal variability and a strong dependence on management events (such as summer plowing at Pappilansuo, fertilization, and harvest at all three sites). The net CO 2 exchange ranged from a strong net uptake at Anttila (–2500 kg C ha −1 yr −1 ) and moderate uptake at Särkisuo (–500 kg C ha −1 yr −1 ) to net release at Pappilansuo (+930 kg C ha −1 yr −1 ). CH 4 fluxes were negligible at Anttila (total of +2 kg CH 4 ha −1 yr −1 ) but reached + 110 kg CH 4 ha −1 yr −1 at Särkisuo and + 51 kg CH 4 ha −1 yr −1 at Pappilansuo. N 2 O emissions peaked after fertilization with + 3.8 (Anttila), + 16 (Särkisuo), and + 29 kg N₂O ha −1 yr −1 (Pappilansuo). Anttila remained a net GHG sink at approximately –8.0 t CO 2 -eq ha −1 , whereas Särkisuo and Pappilansuo were net sources of 5.0 and 12.3 t CO 2 -eq ha −1 , respectively. Anttila had the lowest GHG emissions per kilogram of grass biomass produced and had the highest yield, illustrating the potential for more climate-friendly grassland management on suitable soils. However, the organic soils showed higher GHG emissions. These results highlight the influence of soil type and the importance of management timing on the overall GHG balance in boreal grasslands. • All sites were net emitters of GHGs with the mineral soil grassland emitting the least and producing the highest forage yield. • N 2 O emissions were low when the vegetation was in active growth and demand for soil N was high and vice versa. • Drained peat soils were high methane emitters under inundated conditions within the growing season. • The N 2 O emission factor for the mineral grassland was lower and those for drained peat soils were higher than the IPCC Tier 1 default factor.