Data on humifi cation is important to assessing the rate and magnitude of soil carbo n (C) sequestration. Thus,this study assessed the humifi cation degree (HLIF) of soil organic matter (SOM) and the changes in functional C groups (aromatic-C and aliphatic-C) for contrasting land use and managem ent practices (native vegetation (NV), conventional plow-based tillage (CT) and no-til l (NT) systems) in sub-tropical and tropical Brazilian environments. Experiments we re conducted at Ponta Grossa (PG) in Paraná State and Luca s do Rio Verde (LRV) in Mato Grosso State of Brazil. Laser-induced fl uorescence (LIFS ) and Fourier-transform infrared (FTIR) spectroscopies, were used on whole soil samples to 1-m depth, and on seven aggregate size classes (8–19, 4–8, 2 –4, 1 –2, 0.5–1, 0.25–0.5, 0.053–0.25 mm) obtained by wet sieving of 0–5and5–10 cm layers. Three functional C groups were selected based on FTIR: aliphatic-C 1 (1404 cm− 1), aromatic-C (1632 cm− 1), and aliphatic-C 2 (2852 and 2922 cm− 1). T he HLIF was 3 to 5 times higher at the LRV site than at PG at all soil depths, indicating that selective preservation by aromaticity of SOM is the predominant mechanism in this envi-ronment. Relatively lower HFIL was observed in NT soils at both locations because of aggregation which protects most labile moieties. The depletion of C concentration in CT was related to the decrease in functional C groups (i.e., aromatic-C and aliphatic-C) and an overall increase in the humification degree, indicating that physical pro-tection mechanisms are not suf ficient to protect the labile fractions of OM. In contrast, the intensity of functional C groups under NT systems was similar to that in the soil under NV at both locations. A discriminant analysis of principal components clearly showed that soils at both locations can be clustered into three groups, correspond-ing to the three main land-use and management practices. Thus, soils under NV, NT, and CT differed significantly in terms of the composition of organic compounds, and in the interactions between inorganic and organic frac-tions. Land use changes modify the arrangement of organic compounds necessitating the diversi fication of agroecosystems and conversion to NT farming. Altogether, our results reveal that LIFS and FTIR are fast, efficient, and precise techniques for analyzing the degree of SOC humi fication, functional C groups, and hence the efficien-cy of NT cropping systems in promoting long-term carbon sequestration in soils.