EJSSEurasian Journal of Soil ScienceEurasian J Soil Sci2147 - 4249Federation of Eurasian Soil Science Societieshttp://ejss.fesss.org/10.18393/ejss.2013.2.122-13010.18393/ejss.2013.2.122-130Effects of iron and aluminum oxides and clay content on penetration resistance of five Greek soilsStefanos Stefanou stefst2@cp.teithe.grAgapi Papazafeiriou 22122 - 1302013-05-142013-09-082013-09-152013-10-15 Copyright © 2016 The authors and Federation of Eurasian Soil Science Societies The effect of amorphous and crystalline iron (Fe) and aluminum (Al) oxides and oxy-hydroxides as well as clay on soil penetration resistance of five Greek soils, as a function of soil water suction was studied for the whole range of soil moisture. The soils tested were of loamy texture and were collected from cultivated and non-cultivated areas of north and central Greece (Macedonia and Thessaly). The study aimed at understanding the role of the above mentioned soil components on penetration resistance. The findings showed that the increase of iron and aluminum oxides and oxy-hydroxides content resulted in an increase of soil penetration resistance and the relationships between them were significant. Crystalline iron forms found to have a more profound effect on penetration resistance as compared to amorphous iron forms. Finally, positive and significant relationships were also found between penetration resistance and clay content. However, it is not entirely clear which of the two soil components plays the most important role in penetration resistance changes in soils.Penetration resistance, soil water suction, Fe and Al oxides and oxy-hydroxides, clay