Model experiments on mottle formation simulating field conditions

Creation of soil mottles in four artificial cores with vertically continuous cylindrical pores was accomplished under two different moisture regimes, simulating naturally occurring conditions. Two cores remained permanently unsaturated at a moisture tension of only 7 cm while two others were periodically saturated (three weeks) and drained (one week). Different mottle patterns were produced in each set of cores as a result of the moisture regimes. Mottles in the unsaturated cores were predominantly ped mangans, whereas channel neoalbans and quasimangans were found in the saturated cores. These mottle types correlated well with mottles and moisture regimes in the field. A s semiquantitative analysis using a scanning electron microscope confirmed the visually estimated mottle composition and was used to determine relative movement of iron and manganese in the cores. The latter could be explained by considering the results of in situ redox measurements.