Impact of weather and management practices on greenhouse gas flux dynamics on an agricultural grassland in Southern Finland

Agricultural management and meteorological conditions have a great impact on grassland dynamics, and regenerative and holistic practices especially have significant potential for enhancing soil quality and fertility, biodiversity and carbon cycling in agricultural ecosystems. We monitored CO2 fluxes from an agricultural grassland in Southern Finland with the eddy covariance method over a five-year period together with various meteorological variables to study how weather conditions, rotational grazing, cutting height and other selected management practices affect the fluxes. Additionally, we measured CH4, N2O and CO2 fluxes with the flux chamber method. Interannual variation in the net ecosystem carbon balance (NECB) was substantial as it alternated between −60 (C sink) and 131 g C m−2 yr−1 (C source). Over the whole five years, the site was near neutral with approximately −10 g C m−2. CH4 and N2O fluxes were small in each measured growing season. Field management greatly affected the annual NECB, and rotational grazing had potential positive impact on assimilation efficiency and taller cutting height also showed occasional higher assimilation during regrowth stage. We utilised the measurement data to calibrate a modified version of the BASGRA grassland model for the site, and ran simulations to isolate the impacts of precipitation and air temperature as key drivers for the ecosystem C exchange. The simulations showed that variations in both precipitation and air temperature had distinct impacts on the primary productivity and heterotrophic respiration, causing the ecosystem to alternate between net carbon source and sink during individual years. Over the five-year period, the calibrated model demonstrated net carbon sink (−70 g C m−2 central estimate) into the ecosystem.