Assessing labile organic carbon in soils undergoing land use change in Brazil: A comparison of approaches

The labile organic C (LC) and C management index (CMI) may be useful indicators of alterations of soil organic matter (SOM) in areas undergoing land use change (LUC) for biofuels production. However, there is no consensus on which methodology is best suited for quantifying LC and CMI. The main goal of this study was to assess alterations on LC contents and CMI values in sites undergoing the LUC native vegetation (NV)-pasture (PA)-sugarcane (SC) in south-central Brazil, and evaluated the sensitivity of different methods commonly used to assess LC and CMI, in order to select a best-suited method to quantify these indicators in tropical regions. The conversion NV-PA decreased the LC and CMI, whilst the conversion of PA-SC tended to increase the CMI. Accordingly, cropping sugarcane in areas previously used as pastures, as currently has been observed in Brazil, enhance SOM quality. The methodology used to quantify the LC and the CMI is critical to infer about LUC effects. Both methods proposed by Blair et al. (1995) and Diekow et al. (2005) were highly sensitive to the conversions evaluated in this research. However, Diekow et al. (2005) is the most suitable method to estimate the LC and CMI in sites undergoing LUC in Brazil, since the approach of Blair et al. (1995) notably overestimates these SOM quality indicators. We reiterate that the SOM changes are well expressed by the total soil organic C in areas undergoing LUC and, integrated approaches, such as the CMI, are quite suitable to evaluate the effects of LUC on SOM.