Factors Affecting Oxidation-reduction Processes in an Oxisol with a Seasonal Water Table1
- W. Couto,
- C. Sanzonowicz and
- A. de O. Barcellos2
The weekly fluctuation of the water table was recorded for a period of 2 yr at five sites along a transect of a high plateau area in the Cerrados of Brazil characterized by minimal variation in soil morphology, color, and texture. The soil studied was a Red-Yellow Latosol, a member of the clayey, oxidic, isohyperthermic family of Typic Acrustoxes. The soil profile to a depth of 200 cm did not show mottling or color chromas of 2 or less at any site. However, the water table was within 0.4 to 2.0 m of the soil surface at some sites for more than 90 d yr−1. Bright platinum electrodes installed at three sites showed only a moderate range of Eh values (700-500 mV) indicating that no reduction took place in the soil at any depth, in spite of the standing water table. Soil samples taken at the 0- to 20-, 20- to 40-, 40- to 60- and 60- to 80-cm depth, and subjected to different treatments, were incubated for 90 d at approximately 30 kPa water tension or under waterlogged conditions. Treatments consisted of nutrients, nutrients plus lime, and sucrose at two rates, 0 and 10 g kg−1 of soil. The Fe (II) content measured in moist samples at the end of the incubation period showed that intensive reduction took place under all treatments in soil samples taken from the 0- to 20- and 20- to 40-cm depths. Samples taken below 40 cm contained a high Fe (II) content only when sucrose was applied. These data suggest that reduction does not occur in the field in the lower part of the soil profile even when a high water table is present due to the lack of a source of energy for microbial activity. It is suggested that the organic matter present in the lower part of the soil profile is too stable and/or too low in available nutrients for the reduction process to take place during the water logging period.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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