Soil organic matter fractions under different land uses and soil classes in the Brazilian semi-arid region

Context Land use change (LUC) is considered one of the main factors associated with soil carbon (C) loss worldwide. Aim Evaluate changes in labile and non-labile soil organic matter (SOM) fractions in different land use systems – native vegetation (NV), agriculture with conventional cultivation (CC) and pasture (PA) – in five soil classes in the Brazilian semi-arid region. Methods Soil samples were collected to a depth of 100 cm, and soil C and nitrogen (N) content and stocks were determined and also stocks of labile (LC) and non-labile (NlC) C fractions. In addition, the Carbon Management Index (CMI) was used to evaluate soil health changes. Key results SOC stocks significantly decreased after conversion from NV to CC (by 23%; 0–30 cm) and PA (by 22%; 0–100 cm). Losses due to LUC were greater in the LC than the NlC fraction, and this was reflected in the CMI reducing by 37% for PA and 57% for CC in the 0–100 cm layer. Regarding the different soil classes, LUC reduced SOC stocks only in the Luvisol, Planosol and Leptosol classes, while in the LC fraction, changes were observed in Acrisols, Cambisols and Planosols. Conclusions Clearing NV areas for CC systems and PA reduced the SOC stocks and SOM fractions and, consequently, decreased soil quality. Implications These findings underscore the importance of considering the quality of SOM when evaluating LUC impacts on SOC stocks in the different classes of soil in the Brazilian semi-arid region.