Total organic carbon and the humic fractions of the soil organic matter in silvopastoral system

In agricultural production systems soil organic matter (SOM) is of paramount importance when assessing soil quality. Therefore, the objective of this study was to quantify the total organic carbon (TOC) and the humic fractions of the soil organic matter in silvopastoral system (SS) and to compare them with the conventional pasture system (CP) and a native vegetation area of Cerrado (NV). In the SS, soil samples were collected at distances 2.5, 5.0, 7.5 and 10 m from the eucalyptus row. Soil samples in each system were collected in the 0-10, 10-20 and 20-30 cm layers. The following parameters were determined: TOC, organic carbon associated with minerals (OCam), particulate organic carbon (OCp) and carbon of the humic soil substances. Carbon management index (CMI) and the sum of humic substances (SHs) were also calculated. SS was able to promote larger increases in the TOC, OCam and carbon stocks in the humic fractions when compared to CP and was also able to increase OCp and CMI values in depth. Soil sampling distances in the silvopastoral system had no significant influence on the changes in total carbon stocks and short-term SOM fractions. Furthermore, the land use with two years of SS implementation is not yet able to provide for most of the evaluated attributes with values equal to or higher than the soil with NV.