| heal.abstract |
Soils that are forming on volcanic parent materials have unique physical and chemical properties and in most cases, on wet and humid climates, are classified as Andisols. The main purpose of this study is to examine if the soils that are forming on volcanic materials under a dry Mediterranean climate, in Nisyros Island (Greece), meet the requirements to be classified as Andisols. Soils from seven sites were sampled and examined for their main physico-chemical properties and selective dissolution analysis. Dithionite-citrate-bicarbonate (DCB) extractable Al and Fe (Ál d, Fe d), acid ammonium oxalate extractable Al, Fe, and Si (Ál o, Fe o and Si o), and sodium pyrophosphate extractable Al and Fe (Al p, Fe p) were measured. In addition, Al and Si were determined after reaction with hot 0.5 M NaOH, (Al NaOH and Si NaOH) and with Tiron-(C 6H 4Na 2O 8S 2), (Al T and Si T). P-retention was also measured. The soils are characterised by coarse texture, low organic matter content, low values of cation exchange capacity (CEC), and high pH values. Values of Si o, Al o and Fe o are less than 0.022%, 0.09% and 0.35% respectively, highlighting the lack of noncrystalline components. The ratio (Fe d-Fe o)100/Fe d is quite high expressing the degree of crystallisation of free iron oxides. For all samples tested, values of the Al o + 1/2Fe o index are extremely low (< 0.24%). High Si NaOH and Si T (arising 2.76% and 2.18% respectively) indicate the presence of silica in amorphous forms. P-retention values are very low (< 12.6%). The results indicated the absence of noncrystalline minerals except for amorphous silica, and do not exhibit andic or vitric soil characteristics to be classified as Andisols. © 2006 Elsevier B.V. All rights reserved. |
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