Organic-inorganic interactions in an aridisoil of Oman along vertical and lateral trends of the soluble major, trace and rareearth elements

Abstract

Major, trace and rare-earth elements “(REEs)” dissolved by successive water and acetic-acidleaching of soil samples were quantified along a vertical and a lateral trend relative to areference aridisoil covered by palm trees. The total content of the organic carbon rangesfrom 0.07 to 2.7% with the highest values in the topsoil closely below vegetation, confirminga higher organic activity. The water-removed elements decrease irregularly with depth andwith increasing distance to the vegetated area, the highest concentrations being observed at20 cm depth and 18 m away from vegetation. The nutrients removed by acetic-acid decreasewith depth and until 22 m from vegetation. Maximum leaching was observed in the surfacesample and 32 m away from vegetation. In fact, no straight trends were obtained in both thevertical and horizontal samplings; it looks that the elemental contents of each soil layer areonly representative for themselves. The metallic trace elements are more abundant in thetopsoil than in the subsoil, suggesting some anthropogenic supply. Mainly controlled by solidorganic exudates, the REEs are the only ones with general vertical and horizontal trends: theydecrease at depth, together with an increase laterally away from vegetation. The Ce and Eupositive anomalies increase deeper below the vegetation and away: an oxidation-reductionchange is visible for the former anomaly, probably due to decreasing organic activity. Thelatter anomaly away from vegetation could reflect a larger contribution of soluble minerals tothe leachates.