Partition of CO2 Fluxes to Evaluate Agroecosystem Functional Heterogeneity under Intra-Field Soil Bulk Density Variability

The article presents an algorithmic approach for separation of integral CO2 fluxes for a quantitative assessment of the contribution of field areas with different topsoil bulk densities to the overall carbon balance. The methodology is based on integrating eddy covariance data, dynamic footprint modeling, and digital soil mapping. The experiment was performed in 2023 on spring barley crops under conditions of pronounced soil bulk density heterogeneity (1.45–1.80 g cm–3). The developed approach enabled the partitioning of the total net ecosystem exchange (NEE) into gross primary production (GPP) and ecosystem respiration (Reco) components, specific to the identified zones with contrasting densities. It was established that under the dry conditions of June 2023, overcompacted areas (>1.65 g cm–3) were characterized by higher values of gross primary production (to 14 μmol m–2 s–1) and water use efficiency compared to less compacted areas (<1.65 g cm–3), where these values did not exceed 10 μmol C m–2 s–1. In the second half of the growing season, during the ripening stage and with an increase in precipitation in August, an inversion was observed: GPP values in the overcompacted areas were 2.8 μmol C m–2 s–1, and the Reco intensity was 2.1 μmol C m–2 s–1, which is half the values recorded in areas with lower bulk density (4.2 μmol m–2 s–1). The proposed approach enables quantitative recording of the intra-field variability of carbon balance components without using spatial averaging.