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DFA.Durustands

Key to Great Groups 

DFA. Ustands that have, in 75 percent or more of each pedon, a cemented horizon that has its upper boundary within 100 cm either of the mineral soil surface or of the top of an organic layer with andic soil properties, whichever is shallower. Durustands, p. 316 

DFA. Durustands are the Ustands that have, in 75 percent or more of each pedon, a cemented horizon with its upper boundary within 100 cm either of the mineral soil surface or of the top of an organic layer with andic soil properties, whichever is shallower. Characteristically, Durustands have an ochric epipedon and a cambic horizon above the cemented horizon. The Durustands in the United States generally developed in late-Pleistocene or Holocene deposits. Most formed under coniferous/grass or shrub vegetation. 

Definition 

Durustands are the Ustands that have, in 75 percent or more of each pedon, a cemented horizon with its upper boundary within 100 cm of the mineral soil surface. 

Key to Subgroups 

DFAA. Durustands that have, in one or more horizons at a depth between 50 and 100 cm either from the mineral soil surface or from the top of an organic layer with andic soil properties, whichever is shallower, aquic conditions for some time in normal years (or artificial drainage) and one or more of the following:

1. 2 percent or more redox concentrations; or

2. A color value, moist, of 4 or more and 50 percent or more chroma of 2 or less either in redox depletions on faces of peds or in the matrix if peds are absent; or

3. Enough active ferrous iron to give a positive reaction to alpha,alpha-dipyridyl at a time when the soil is not being irrigated. Aquic Durustands 

DFAB. Other Durustands that have, at a depth between 25 and 100 cm either from the mineral soil surface or from the top of an organic layer with andic soil properties, whichever is shallower, a layer 10 cm or more thick with more than 3.0 percent organic carbon and the colors of a mollic epipedon throughout, underlying one or more horizons with a total thickness of 10 cm or more that have a color value, moist, 1 unit or more higher and an organic-carbon content 1 percent or more (absolute) lower. Thaptic Durustands 

DFAC. Other Durustands that have a melanic, mollic, or umbric epipedon. Humic Durustands 

DFAD. Other Durustands. Typic Durustands 

Definition of Typic Durustands 

Typic Durustands are the Durustands that:

1. Do not have, in any horizon at a depth between 50 and 100 cm either from the mineral soil surface or from the top of an organic layer with andic soil properties, whichever is shallower, both aquic conditions and any of the following:

                a. 2 percent or more redox concentrations; or

                b. A color value, moist, of 4 or more and 50 percent or more chroma of 2 or less either in redox depletions on faces of peds or in the matrix if peds are absent; or

                c. Enough active ferrous iron to give a positive reaction to alpha,alpha-dipyridyl at a time when the soil is not being irrigated;

2. Do not have, between depths of 25 and 100 cm, a layer 10 cm or more thick with more than 3.0 percent organic carbon and the colors of a mollic epipedon throughout, occurring below a horizon or horizons 10 cm or more thick with a color value, moist, 1 unit or more higher and an organic-carbon content 1 percent or more lower; and

3. Do not have a melanic, mollic, or umbric epipedon.

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