Laboratory comparison of soil redox conditions between red soils and brownsoils in Minnesota, USA

Certain soil morphological characteristics create significant problems for hydric soil identification due to lack of commonly observable Fe-based redo ximorphic features that indicate seasonally saturated and reduced condition s. Examples include soils with high levels of organic C and red soils (7.5Y R or redder) containing high amounts of hematite iron. The objectives of th is research were to examine the effects of organic C content and Fe mineral ogy on (i) soil redox response and (ii) the development of Fe-based redoxim orphic features. Redox reactions related to the fundamental biochemical pro cesses that occur in saturated soils were studied in a controlled laborator y experiment. The experimental design included six columns of red soils (5Y R) from northeastern Minnesota and six columns of brown soils (10YR), posse ssing varying organic carbon contents, from southeastern Minnesota. Redox m easurements taken throughout the experiment suggest different soil redox en vironments between the brown and red soils. The brown soils had redox poten tials that decreased gradually and then remained at a constant decreased st ate around 0.0 mV. Redox potentials for the red soils decreased rapidly and equilibrated in the range of 100 to 300 mV. Variations between these soil responses may be due to different Fe-oxide mineralogies and/or the amount o f bioavailable organic carbon.