Andisols from Four Different Regions of Iceland

Limited information has been published on Andisols in Iceland, but such data are important for understanding the erosional and periglacial processes that are intense in Iceland. The objectives of this research were to investigate Andisols that developed in tephra and eolian materials and that are highly susceptible to soil erosion, and to evaluate the effectiveness of the recently established Andisol order for providing meaningful classes in Iceland. Four soils that formed in 1- to 3-m-thick tephra and eolian materials of various origins were studied. The soils have low bulk density (<0.8 g cm⁻³), high −0.033 and −1.5 MPa water retention (0.27–1.18 and 0.17–0.85 kg kg⁻¹, respectively, excluding tephra horizons), and Atterberg limits characteristic of field-moist Andisols (plastic limits of 0.49–0.95 kg kg⁻¹ and liquid limits of 0.54–0.97 kg kg⁻¹). Soil reaction (H₂O) ranges between pH 5.6 and 6.7. Organic C contents are high but erratic; they range from 21 to 90 g kg⁻¹, excluding thick tephra horizons that are characteristically low in C. Soil color was not related to organic C content. The cation-exchange capacity is generally high (22–46 cmolc kg⁻¹) and is highly related to organic C, oxalate-extractable Al + Fe, and precipitation (R² = 0.92). The <0.002-mm fraction is dominated by allophone and ferrihydrite represented by high oxalate-extractable Al, Fe, and Si. High organic C content was not found to inhibit allophone formation in surface horizons. These Andisols developed from sediments of complex history consisting of tephra layers deposited during episodic volcanic events that are interstratified with eolian polycycled materials of glacial-fluvial and andic origin. Assigning buried horizons and lithological discontinuities was difficult and often arbitrary and was not done for the eolian and tephra materials. All the pedons were classified as Haplocryands. More than 60 000 km² of Andisols may occur in Iceland, which would constitute 5 to 6% of all Andisols in the world.