Agglutination of clay particles in tropical soils is not well studied although it is already known process in the savannah conditions. This research had the objective to verify clay behaviour in the savannah latosoils from Gouveia and also to detect possible causes of it. The B-horizon of soil collected on the upper slopes, and developed over three different lithologies: schist, granite and metabasic rocks, was analysed. Two granulometric analyses were conducted: with NaOH and H₂O. Silt particle was treated with DCB, DRX, Mössbauer spectrometry and MEV to determine physical and chemical differences between the types of soil from the three lithopedological domains. The results of the texture using two different dispersants show great variation. There is a significant increase in the percentage of clay after the treatment with NaOH, indicating the occurrence of aggregation of this particular size that is not detected when only H₂O is used as dispersant. The most representative variation of the percentage of clay is that of soil from metabasic rocks, richer in iron content. Treatment with DCB, which takes away crystalline iron oxides, shows even more expressive results with the increase of clay in detriment especially of silt percentages, although percentage of fine sand has also shown decrease. X-ray difractometry of the samples demonstrated the predominance of aluminosilicates minerals. The EM detected the presence of ghoetit and hematite in all soil samples, and of maghemetit in those of metabasic rocks. The results of the MEV show a hierarquization in the aggregates micromorphology. These macroaggregates as well as the voids size are bigger in the soils from schist. In contrast, in the soils from metabasics the aggregates and the voids are smaller and less frequent. Soils from granite show intermediated characteristics of both previous ones. The results draw the attention to the agglutination capacity of iron oxide, although aluminium and silica can also be involved. A better understanding of this process in tropical environments is of fundamental importance because of its influence on hydrological behaviour of soils.
*This research was financially supported by FAPEMIG.