Keys to Soil Taxonomy: Suborders

Code	Name	Description
IA	Albolls	Mollisols that have: An argillic or natric horizon; and An albic horizon that has chroma of 2 or less and is 2.5 cm or more thick, has its lower boundary 18 cm or more below the mineral soil surface, and either lies directly below the mollic epipedon or separates horizons that together meet all of the requirements for a mollic epipedon; and In one or more subhorizons of the albic horizon and/or of the argillic or natric horizon and within 100 cm of the mineral soil surface, redox concentrations in the form of masses or concretions, or both, and also aquic conditions for some time in normal years (or artificial drainage).
IB	Aquolls	Other Mollisols that have, in a layer above a densic, lithic, or paralithic contact or in a layer at a depth between 40 and 50 cm from the mineral soil surface, whichever is shallower, aquic conditions for some time in normal years (or artificial drainage) and one or more of the following: A histic epipedon overlying the mollic epipedon; or An exchangeable sodium percentage (ESP) of 15 or more (or a sodium adsorption ratio [SAR] of 13 or more) in the upper part of the mollic epipedon and a decrease in ESP (or SAR) values with increasing depth below 50 cm from the mineral soil surface; or A calcic or petrocalcic horizon that has its upper boundary within 40 cm of the mineral soil surface; or A mollic epipedon, with chroma of 1 or less, that extends to a lithic contact within 30 cm of the mineral soil surface; or One of the following colors: Chroma of 1 or less in the lower part of the mollic epipedon;¹ and either Distinct or prominent redox concentrations in the lower part of the mollic epipedon; or Either directly below the mollic epipedon or within 75 cm of the mineral soil surface if a calcic horizon intervenes, a color value, moist, of 4 or more and one of the following: 50 percent or more chroma of 1 on faces of peds or in the matrix, hue of 10YR or redder, and redox concentrations; or 50 percent or more chroma of 2 or less on faces of peds or in the matrix, hue of 2.5Y, and redox concentrations; or 50 percent or more chroma of 1 on faces of peds or in the matrix and hue of 2.5Y or yellower; or 50 percent or more chroma of 3 or less on faces of peds or in the matrix, hue of 5Y, and redox concentrations; or 50 percent or more chroma of 0 on faces of peds or in the matrix; or Hue of 5GY, 5G, 5BG, or 5B; or Any color if it results from uncoated sand grains; or Chroma of 2 in the lower part of the mollic epipedon; and either Distinct or prominent redox concentrations in the lower part of the mollic epipedon; or Directly below the mollic epipedon, one of the following matrix colors: A color value, moist, of 4, chroma of 2, and some redox depletions with a color value, moist, of 4 or more and chroma of 1 or less; or A color value, moist, of 5 or more, chroma of 2 or less, and redox concentrations; or A color value, moist, of 4 and chroma of 1 or less; or At a depth between 40 and 50 cm from the mineral soil surface, enough active ferrous iron to give a positive reaction to alpha,alpha-dipyridyl at a time when the soil is not being irrigated.
IC	Rendolls	Other Mollisols that: Have a mollic epipedon less than 50 cm thick; and Do not have an argillic or calcic horizon; and Have, either within or directly below the mollic epipedon, mineral soil materials less than 7.5 cm in diameter that have a CaCO₃ equivalent of 40 percent or more; and Have either or both a udic moisture regime or a cryic soil temperature regime.
ID	Cryolls	Other Mollisols that have a cryic soil temperature regime.
IE	Xerolls	Other Mollisols that have either a xeric moisture regime or an aridic moisture regime that borders on xeric.
IF	Ustolls	Other Mollisols that have either an ustic moisture regime or an aridic moisture regime that borders on ustic.
IG	Udolls	Other Mollisols.

Source: Keys to Soil Taxonomy, Eighth Edition. 1998.

Links:
Keys to Soil Taxonomy > Orders > Suborders