In Argentina, redox processes have been studied in natural ecosystems, but little is known about these processes in managed environments. In Buenos Aires province (southern Pampean region), large-scale experiments aimed at commercial rice production have recently taken place in low-lying areas of the Depressed Pampa. The objective of this study was to establish the physicochemical modifications that take place in rice field soils as a result of temporary flooding. Soils (fine, illitic, thermic Vertic Argiudolls) developed in loessial sediments are widespread in level interfluves of the La Plata river basin. We measured Fe2+, Mn2+ and NO3 - in the Ap and BA horizons of an artificially flooded and a nonflooded soil during two rice cultivation cycles. Periods of preflooding, flooding, and postflooding were distinguished in each cycle. Only the Ap horizon presented a definite reduced condition during the flooding period, as indicated by redox potential and the contents of Fe2+, Mn2+ and NO3 -. After irrigation was discontinued, the soil returned to an oxidizing state similar to that of the nonflooded soil. The anaerobic conditions did not persist long enough to modify the morphology of the flooded soil as no macroscopic redoximorphic features were observed.
