Estimates for Carbon Stocks in Soil under Humid Grassland Areas in the Federal District of Brazil

Abstract

The soils that lay below humid ecosystems are characterized as being significant holders of carbon. Because of the great susceptibility of this type of environment to anthropic changes, expressive quantities of carbon stored in the soil can be released into the atmosphere. In the Cerrado biome (Brazil), only a few types of vegetation have had carbon storage levels in their soil estimated. The main purpose of this study was to obtain basic quantitative parameters for carbon storage and to identify the general aspects of soil in regions where there exists Humid Grasslands (Campo Limpo úmido), a kind of humid area phytophysiognomy found in the Cerrado. We selected 6 regions of the Federal District with this kind of vegetation formation, characterized by low anthropic impact and located either in the interior or in the proximity of specially protected areas. In each one of the sampled regions, we marked a transect with 4 equidistant points and collected material at 7 different levels of depth: 0 - 5, 5 - 10, 10 - 20, 20 - 30, 30 - 40, 40 - 50 and 50 - 60 cm. We obtained 168 samples, with 84 related to Humid Grassland areas in gleysols and 84 samples related to areas in plinthosols—types of soil dominant in this environment. We determined the texture, bulk density and concentration of nitrogen and carbon at each depth. The average concentration of carbon for Humid Grassland areas was 55.19 g.kg-1, with an average of 61.65 g.kg-1 for Gleysols and 48.73 g.kg-1 for Plinthosols. The soil samples displayed distinct textural differences between gleysols and plinthosols. There were no significant differences in soil density (0.75 kg.dm-3 for Gleysols and 0.72 kg.dm-3 for Plinthosols). The average concentration of nitrogen was 20.66 g.kg-1, with 23.98 g.kg-1 for Gleysols and 17.34 g.kg-1 for Plinthosols. The average carbon storage for Humid Grassland areas, down to 60 cm deep, was 244.17 mg C ha-1 and the total estimated stock for these areas in the Federal District was 206.71 Gg.C. In general, the samples obtained in gleysols showed a carbon content and nitrogen level superior to those in plinthosols, although a greater sampling effort is needed to confirm the differences observed. The density values of stored carbon in the soil beneath Humid Grassland areas proved to be superior to those values observed for other types of vegetation typical for the Cerrado environment.