Carbon and nitrogen stocks under different management systems in the Paraiban "Sertão"

The change in land use leads to significant changes in carbon (C) and nitrogen (N) stocks in the soil and consequently in the global cycle of these elements. The purpose of this study was to evaluate C and N stocks in soils under different management systems in the Paraiban “Sertao”. This study was carried out in the watershed of Val Paraiso stream, State of Paraiba, Brazil. The climate is warm tropical with severe drought, reaching over 35°C in times of higher temperatures. The vegetation is basically composed of Caatinga Hiperxerofila and the predominant soil in this area is classified as Vertisol. The following systems treatments were tested: native vegetation, sparse vegetation, pasture, annual and permanent agriculture. Soil sampling was performed in four respective sites (four profiles). Samples were stratified in four layers: 0-10, 10-20, 20-30 and 30-40 cm. Soil attributes determined and calculated were: bulk density, organic C and N contents, and C and N stocks. The lower values of bulk density were presented in the area of native vegetation and in 0-10 cm soil layer, compared to other management systems and layers. The implementation of agricultural systems in areas that had native vegetation decreased the C and N contents and stocks, in the same way, these values decreased relative soil layers analyzed. The agricultural production and livestock systems are functioning as CO2C emitter when compared with the native vegetation.