Reduction–Oxidation Effects on Soil Potassium and Plant Uptake.

Potassium ions (K+) may become “fixed” between adjacent phyllosilicate layers under waterlogged conditions, rendering K less available to plant uptake. This phenomenon was investigated under greenhouse conditions to determine if K fixation due to biogeochemical reduction contributed to the K deficiency in corn (Zea mays L.) in the northern Great Plains (South Dakota). The objective of this study was to evaluate the effects of a single reduction–oxidation (redox) event on soil K fractions and plant K uptake in montmorillonitic soils. Surface soil (Udolls, 0–15 cm) was collected from various sites across east-central South Dakota and used in a completely randomized greenhouse pot study ( 2×4 factorial). Reduced (Re) and reduced/reoxidized (Re/Ox) treatments were established, and corn was grown to the V5 stage of growth in a two cropping sequence. Potassium levels among soil K fractions did not significantly change upon the redox event. Dry matter (DM) yields were not significantly affected by the redox event. Cumulative K-uptake ranged from 25.7 to 33.2 mg K (kg soil-1), and there were no significant differences between treatments. No increase in K fixation was observed as the result of a single reduction–oxidation event. A single redox event does not cause K fixation in four montmorillonitic soils studied under greenhouse conditions. [ABSTRACT FROM AUTHOR]