Properties and genesis of Argialbolls in the USA

• Albolls in USA have mollic over albic and argillic horizons.
• Argialbolls form in silty materials and have restricted drainage.
• Argialbolls comprise 18,078 km2 in USA (0.02% of land area), 70% in 4 Great Plains states.
• Argillic horizon causes seasonal hydomorphic conditions.

The presence of an albic horizon below a mollic epipedon has long puzzled pedologists. The purpose of this study was to utilize data from the Natural Resources Conservation Service (NRCS) databases and the published literature to develop a weight-of-evidence assessment of how Albolls form in the USA. There are 69 Albolls soil series in the NRCS database, all of which are Argialbolls. These soils contain horizons with the following mean thickness and standard deviation: mollic epipedon (29 ± 11 cm), albic (18 ± 9 cm), and argillic (75 ± 37 cm). Argialbolls comprise 18,078 km2 in the USA (0.02% of total land area), 70% of which occur in North Dakota, South Dakota, Missouri, and Iowa. Argialbolls are somewhat poorly drained, poorly drained, or very poorly drained (78%); and 81% of the Argialbolls are very deep (> 1.5 m). Silty alluvium and loess comprise 86% of the parent materials. The dominant vegetation is grassland (64%), sedges (16%), or savanna (16%). Ninety percent of the Argialboll soil series are in the fine or fine-silty particle-size classes; 62% have a mesic soil-temperature regime; 36% have an aquic soil-moisture regime, and 64% have a smectitic soil-mineral class. The Argialbolls have formed under modern conditions where development of a smectitic-rich argillic horizon has led to reducing conditions during which Fe and Mn concentrate as concretions in the albic horizon that underlies the mollic epipedon.

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