Soil C and GHG Fluxes by 2075 in Key Agricultural Lands of Southern Brazil

The subtropical highlands of southern Brazil (Planalto) have been cultivated for more than 125 years following the conversion of the Atlantic Forest and Pampas grasslands. Previous applications of the DAYCENT model performed adequately to simulate C and GHG dynamics. Our objective was to apply the DAYCENT model (v. 4.91) in this context to simulate soil organic carbon stocks (SOCS) and GHG emissions until 2075 under current and alternative cropping systems under future climate (AR6 – SSP_4.5&8.5). We evaluated perennial pasture (PP), integrated crop‑livestock‑forestry (ILPF), forestry (FOR), and native vegetation restoration (NVR).

Initially, a geospatial database was compiled covering SOCS, soil classes, original vegetation, and 4 climate zones that cover the Planalto. Subsequently, multiple DayCent simulations were performed for soil–vegetation–climate units (33 in total) overlaid with historical cropping data (38 combinations) until 2024. These provided the baseline for future projections to 2075. Simulations were conducted in R with a suite of novel scripts.

Model output indicated higher SOCS under ILPF, NVR and PP, particularly under more extreme climate (SSP8.5). SOCS did not increase under FOR. N₂O fluxes were also influenced by future climate: higher emissions were simulated under alternative systems, except for eucalyptus (FOR), which maintained similar fluxes across all climate scenarios. SOCS and GHG outputs were mapped in GIS to visualize regional patterns and to aggregate SOCS and GHG emissions. Overall, our research revealed the spatial and temporal dynamics of SOC and GHG in the Planalto region of Rio Grande do Sul and projected their trajectories under alternative cropping systems.