Two Physiographic Units Impact on Origin and Distribution of Extractable Iron Oxide Forms in Some Soils of Southern Ahar

Iron is one of the most essential and effective elements in soil forming processes. The amount and distribution of extractable Fe forms in profile indicate the stage and degree of soil development. Because of the physiographic unit importance in pedogenic processes, the effect of physiographic unit in soil forming and development can be investigated based on the amount and distribution of iron forms. This research has been is done in two different physiographic units of piedmont (slope of %2-5%) and hill (slope of %8-15%) as low and highland, which are located in southern Ahar, East Azerbaijan province. For this purpose, various forms of iron in three profiles of each unit (totally six profiles) were measured by pyrophosphate, oxalate and dithionate extractants. The average amount of crystallized iron was obtained 2.876 g kg^-1 for downstream physiographic unit and 4.76 g kg^-1 for upstream physiographic unit which statistically means comparison is significant. The mentioned results confirm increment of crystalline iron oxides and decrease of amorphous forms and bounded with organic matter in highland in comparison with lowland. Also in this research, some of soil physical and chemical characteristics were measured using standard methods and correlation between different forms of iron was evaluated. According to the relationship between soil age and different forms of iron, it can be said that the highland soils are more developed than the lowland soils, and these results are accommodated with geomorphologically unit type, clay percentage, solum depth, and relative amount of kaolinite mineral.