ANDISOLS OF MADEIRA ISLAND (PORTUGAL) - CHARACTERISTICS AND CLASSIFICATION

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