Dynamics of soil organic matter in a cultivated chronosequence in the Cerrado (Minas Gerais, Brazil)

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The vegetation of the Cerrado has been replaced by pastures and agriculture, affecting the stock and dynamic of soil organic matter (SOM). The present study was conducted in a cultivated chronosequence with a mixed system (agriculture + pasture for 15 years; Agric+P15) and cultivated pasture (30 years; P30), taking the native Cerrado as a reference to assess changes in the stock of SOM, the dynamics (d13C) and the carbon replacement derived from the C3 in native vegetation to C4 in cultivated vegetation. Compared to Cerrado, there was a reduction in C stock in cultivated soils at 0–15-cm depth (reduction of 26.5% in Agri+P15 and 6% in P30). The close similarity between Cerrado and P30 indicates that the pasture management enhanced the stock relative to Agri+P15, but was not effective in sequestering C. Only in the 0–15 cm depth was there a marked replacement of C derived from the C3 of Cerrado plants associated with cultivation time. In the chronosequence, the isotopic signature of C4 plants dominated in the soil below 30 cm depth, suggesting a paleoclimatic effect on SOM.