Carbon storage in clayey Oxisol cultivated pastures in the Cerrado region, Brazil

Carbon accumulation in soil under pasture is seen as a process of decreasing greenhouse gases concentration in the atmosphere. Thus, tropical areas such as the Cerrado region in Brazil, with an area of 204 million ha and of around 50 million ha of cultivated pastures, most of them with African grasses, are considered potential areas to sink carbon. Total carbon in soil profile was used to compare carbon accumulation among cultivated and native pastures on a Dark Red Latosol (Typic Haplortox) found in the Cerrado region, Brazil. Soil samples taken at 1.0 m deep were analyzed in seven different fields: native pasture (1), Panicum maximum (2), Brachiaria decumbens (3), Brachiaria brizantha + Stylosanthes guianensis (4), Andropogon gayanus + Neonotonia wightii + Centrosema brasilianum (5), two seed production fields, B. brizantha (6) and Paspalum atratum (7). Forage dry matter production was also evaluated at each field. All cultivated pastures were over three years old and grazed under different stocking rates, except for fields 6 and 7, which were not grazed. Dry matter production was higher in fields 6 and 7 and lower in fields 1, 3 and 5. An ongoing degradation process was detected in fields 3 and 5. Carbon storage amounted to 100 Mg ha(-1) in I and ranged from 97 Mg ha(-1) in 3 to 113 Mg ha(-1) in 2, 6 and 7. Pastures in fields 3 and 5 (low shoot dry matter production and low fertility status), had less soil carbon than fields 6 and 7 (higher shoot dry matter production and better fertility status). Total soil carbon and forage dry matter production showed a high correlation (0.83, P < 0.02), demonstrating that carbon accumulation was dependent on shoot biomass production, which is a result of the soil fertility status. Presently, most of the 50 million ha of cultivated pastures in the Cerrado region have been poorly fertilized and unadequately grazed. Results from this study showed that soil carbon accumulation in degraded pastures or in those under an ongoing degradation process does not contribute significantly to the sinking of atmospheric CO2 as well as to the reduction of greenhouse gases concentration in the atmosphere. (C) 2004 Elsevier B.V. All rights reserved.