Carbon Balance at the Regional Scale in Southern Brazil Estimated with the Century Model

Abstract

Modeling of soil organic C (SOC) dynamics associated with GIS can be useful to estimates C emissions and sequestration as a function of the changes in the land use and soil management. A balance of C emissions and sequestration was made at the regional scale using the Century model and GIS. Santana district in Ijuí, RS (28° 20′S and 53° 53′W) was selected where occur Hapludox, Orthents, Argiudolls, and Fluvents are common. We identified four homogeneous areas based on cropping systems, soil tillage systems, and native vegetation. These areas were converted into agriculture at different times. Soil samples were taken at 0–20 cm depth. The Century model was calibrated and validated based on the sampled areas and their estimates were generalized. We defined different simulation units that are similar zones in soil class, landscape elements (hilltops, slope, and depositional areas) and time of agricultural use (1901, 1957, 1965, 1976, and 1988). The agriculture use caused a 50 % reduction in SOC stocks from 1900 to 1986 (from 550.9 to 276.8 Mg × 10³), by the end of most intensive soil management period, which corresponded to emissions of 2,277.5 × 10³ Mg of CO₂ into the atmosphere. Moreover the adoption of conservation agriculture management in 1987 enabled the recovery of C content of the soil. It is considered for 2007, compared with the original, recovery of the SOC stock in up to 60 % (337.7 × 10³ Mg) when the soil C balance was positive in 276.5 × 10³ Mg of CO₂. These results shows the CO₂ potential emission to the atmosphere by the forests removal and burning, as well as the potential of soil C sequestration by the adoption of soil conservation tillage systems. Century model adequately estimated the evolution of SOC stocks and CO₂ balance due to the use, land use changes, and soil management.