Saturday, 15 July 2006

Iron Oxides Distribution and Soil Color Studies of Well-drained Alfisols in Semi-arid Environment (Greece).

Pantelis E. Barouchas1, Nikolaos C. Moustakas2, Leonidas Panagiotopoulos1, and Athanasios Koulopoulos1. (1) Technological Educational Institute of Messolonghi, Faculty of Agricultural Engineering & Water Resources, Nea Ktiria, Messolonghi, 30200, Greece, (2) Agricultural Univ of Athens, Laboratory of Soil Science and Agr. Chemistry, Lera Odos 75, Athens, 11855, Greece

Six pedons, three from alluvial deposits in Thessaly Central Greece (38o37'N, 21o23'E) and three from alluvial deposits in Agrinio, Western Greece (39o38'N, 22o35'E) were selected, sampled and studied focusing on iron oxides distribution and color characteristics. The soils belong to the soil order of Alfisols. In Greece, Alfisols are widespread and considered as an important soil resource. Their occurrence has been recorded under different geomorphic surfaces and drainage conditions. They can be grouped in two large categories: (1) the autochthonous or residual and (2) the allochthonous. Alfisols in Greece can be found on hard limestone and basic igneous rocks in sloping mountainous or hilly landscapes. This type of soils is important for agriculture, as well as for the geoarchaelogical context. The soils developed on Quaternary alluvial deposits mainly derived from hard limestone and are characterized of good drainage (in both areas) and classified as Typic Rhodoxeralf and Typic Haploxeralf, according to Soil Survey Staff. The climate in both areas is thermo-Mediterranean, characterized by hot dry summers and cold humid winters. The average annual rainfall over a 30-year period in Agrinio area is 1022 mm and over a 50-year period in Thessaly area is 426 mm. The soil moisture and temperature regime is xeric and thermic, respectively in both areas. The particle size distribution on a clay free basis (i), the cumulative particle size distribution (ii) and the sand/silt ratio on a clay free basis (iii) were calculated. Distribution of sand and silt with depth on a clay-free basis is almost steady for all pedons, approaching the base of Bt2 horizon except pedon P6 in Agrinio area where sand increases with depth. In all cases cumulative particle distribution suggesting uniformity of parent material at time t=0. The mean value of dithionate-extractable iron oxides was 21.08 g kg-1 (n=18, stdv = 11.47) and 22.4 g kg-1 (n=15, stdv = 7.3) for Thessaly and Agrinio area, respectively. The mean value of oxalate iron oxides was 1.9 g kg-1 (n=18, stdv=0.53) and 5.0 g kg-1 (n=15, stdv=2.8) for Thessaly and Agrinio area, respectively. For pedons P1, P3 in Thessaly area and P6 in Agrinio area, the value of Feo increases from A to B-horizon probably because organic matter inhibited crystallization although organic matter was not correlated with Feo. The Fed was not correlated with Feo, indicating that crystallization of iron oxides is not a function of the same pedogenetic factor. In addition, the Fed/clay ratio is not steady with depth suggesting that clay and free iron oxides have not been co-migrated. According to x2 Bartllet's test there was homogeneity of soil materials in the studied areas, so an analysis of variance was performed to provide a comparison of color properties, pedogenetic indices and different forms of iron between the two areas. Rainfall was assumed to be the source of variation. The primary assumption that rainfall was the main factor, which control their color and pedogenetic characteristics were not confirmed. Additionally pedogenetic indices could not be used to distinguish the developed soils of Thessaly and Agrinio area. Results indicated a statistically significant correlation between Munsell value and chroma with amorphous oxides. Probably, an isomorphous replacement of Fe for Al, as indicated by the second derivative spectroscopy analysis has been done. In both areas goethite is the prevalent iron oxide according to second derivative spectroscopy analysis of soil samples.

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