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PEDOLOGY

Soil Organic Carbon Stocks of Rio Grande do Sul, Brazil

^a Deparamento de Solos, Univ. Federal do Rio Grande do Sul, 90470-230 Porto Alegre,RS,Brazil
^b Centro de Energia Nuclear na Agricultura, Univ. de São Paulo, 13400-970 Piracicaba, SP Brazil
^c UR SeqC, Institut de Rechereche pour le Développement, 3400 Montpellier, France

^* Corresponding author (carlos.tornquist{at}ufrgs.br).

Robust and accurate regional estimates of C storage in soils are currently an important research topic because of ongoing debate about human-induced changes in the terrestrial C cycle. Widely available geoprocessing tools were applied to estimate native soil organic C (SOC) stocks of Rio Grande do Sul state in southern Brazil to a depth of 30 cm from previously sampled soil pedons under undisturbed vegetation. The study used a statewide comprehensive soil survey comprising a small-scale soil map, a climate map, and a soil pedon database. Soil organic C stocks under native vegetation were calculated with two different approaches: the Tier 1 method of the Intergovernmental Panel on Climate Change (IPCC) and a refined method based on actual field measurements derived from soil profile data. Highest SOC stocks occurred in Neossolos Quartzarênico hidromórfico (Aquents), Organossolos Tiomórficos (Hemists), Latossolos Brunos (Udox), and Vertissolos Ebânicos (Uderts) soil classes. Before human use of soils, most C was stored in the Latossolos Vermelhos (Udox) and Neossolos Regolíticos (Orthents), which occupy a large area of Rio Grande do Sul. Generally, IPCC default reference SOC stocks compared well with SOC stocks calculated from soil pedons. The total SOC stock of Rio Grande do Sul was estimated at 1510.3 Tg C (5.8 kg C m^–2) by the IPPC method and 1597.5 ± 363.9 Tg C (7.4 ± 1.9 kg C m^–2) calculated from soil pedons. The SOC digital map and SOC database developed in this study provide crucial background information for state-level contemporary assessment of C stocks and soil C sequestration programs and initiatives.

Abbreviations: GIS, geographic information system • IPCC, Intergovernmental Panel on Climate Change • SOC, soil organic carbon