ANDISOLS OF MADEIRA ISLAND (PORTUGAL) - CHARACTERISTICS AND CLASSIFICATION

This paper reports the morphological, physical, chemical and mineralog ical features of seven pedons selected to represent the major types of Udands occurring in Madeira Island. All of these pedons showed simila r high contents of organic matter (60 g kg-1 of C and often more) to d epths of more than 40 cm. Despite this similarity, only three pedons h ad the colour requirements of Fulvudands; the others had colour values too high to meet the criterion. This was attributed to the high amoun ts of hematite masking the dark brown colour of organic colloids. As t estified by their variable total reserve in bases (TRB) and their vari able contents of allophane, Andisols of Madeira have reached different stages of weathering; the most weathered ones are very acid (alic) an d very rich in total Fe2O3; they qualify as non-allophanic Andisols. I t is suggested that the pyroclastic parent materials of these highly w eathered Andisols had been altered prior to the present pedogenetic cy cle. Such a hypothesis would explain their mineralogy characterized by high lithogenic hematite and low weatherable minerals contents. In su ch non-allophanic Andisols, the andic soil properties are probably due mainly to Al-humus complexes, accompanied by some ferrihydrite.