Fatores de mudança nos estoques de carbono do solo devido ao uso da terra no semiárido brasileiro.

Abstract

The increase in concentrations of greenhouse gases (GHG) in the atmosphere, its relation with global warming, and consequently with climate change, has been widely studied by the scientific community. The studies indicate that the land use change is a key element in the carbon (C) sequestration or GHG emission, due to the soil being the largest C reservoir of the terrestrial surface. Thus, it is important to quantify GHG emissions or the C sequestration potential of agricultural systems. In this sense, the objectives of this research were to evaluate the impacts promoted by the conversion of native vegetation to agricultural systems (pasture, annual and perennial crops) on soil C stocks in the Brazilian semi-arid region, through a meta- analysis and derivation of the specific SOC stock change factors in the semi-arid region of Brazil. To achieve these objectives, this study includes soil sampling and a literature review with soil C data in the main agricultural systems of the Brazilian semi-arid region. Briefly, with the meta-analysis, it was estimated that the agricultural systems in areas previously occupied by native vegetation (Caatinga) in the Brazilian semi-arid, promotes reductions in C stocks, with an average response rate of 0.83. The average losses varied between 4% and 35% depending on the time, type of land use, soil depth and mineralogy. The change factors in C stocks indicate that conventional systems with annual crops reduce soil C stocks by 17%, 13% and 4% in the 0-30, 0-50 and 0-100 cm soil layers, respectively, after 20 years of conversion. However, losses of soil C increase with the crop period, since the derived factors for 40 years showed a decrease of 26%, 22% and 13% for the layers 0-30, 0-50 and 0-100 cm, respectively, in relation to the soil C stocks of native vegetation. In conventional systems with perennial crops, the losses were 29% in the 0-30 cm layer after 20 years of land use in relation to the C stocks of the native vegetation soil. For pastures, management factors show reductions in C stocks between 12% and 27% depending on the time of use and the soil layer. In addition, they suggest that losses occur in the first five years after conversion of native vegetation; however, there is a tendency to recover C stocks over time, reaching 4% after 30 years of pasture use.