Saturation, reduction, and redox morphology of seasonally flooded alfisols in Taiwan

Anthraquic conditions were defined in the soil taxonomy primarily for rice paddy soils, but little data have been published on relationships among saturation, reduction, and morphological features for such soils. We studied those parameters in three alternatively hooded and irrigated rice-growing Alfisols. Redoximorphic features were evaluated using morphological descriptions. Saturation was monitored at depths of 50 and 100 cm using unlined boreholes and perforated wells. Reduction was evaluated by both measurements of redox potential and reaction to alpha,alpha'-dipyridyl dye. The Siaoli soil (Typic Plinthaqualf) was saturated at 100 cm for virtually the entire year, and was saturated at 50 cm for 44% of the year. Reducing conditions occurred at the 50-cm depth. The Potu soil (Plinthaquic Paleudalf) was saturated at 50-cm depth for 25% of the year, and at 100-cm depth nearly 50% of the year. Reduction varied with depth, but did not necessarily correspond to periods of saturation. The Luchu soil (Plinthic Paleudalf) was saturated at 50 cm for 36% of the year, and was not saturated at 100-cm depth throughout the year. Reducing conditions were observed frequently at 50 cm, but were never observed at 100 cm. All the soil pedons had redoximorphic features, and nodule size decreased in the sequence Potu > Siaoli > Luchu. All soils met the requirements for aquic conditions but the Luchu soil was marginally oxyaquic.