Abstract
Ferralsols correspond to the red and yellow soils that are common in the tropics. They are deeply weathered but physical fertility is high because they exhibit a strong microgranular structure whose origin is still actively debated. In the present study, we looked for evidence of the biological origin of the structure resulting from soil fauna activity. We present results recorded with Brazilian Ferralsols developed under native vegetation. It was found that the Ferralsols studied exhibit morphological features related to the activity of social insects. We showed the presence of potassium 2:1 clays originating from the saprolite in the microaggregates of all the Ferralsols studied. These 2:1 clays were earlier discussed as markers of long-term termite activity. This highlights the threat that weighs on the physical fertility of these soils, and more broadly on the water cycle in the tropical regions concerned, if intensive agriculture reduces the soil fauna biodiversity, as indicated by several studies.