Humic Podzol (HP)
These soils have a dark-colored podzolic B horizon that contains very little extractable Fe. They occur typically in wet sites so that they are saturated with water during some periods of the year. Characteristically they occur under heath, forest and heath, sphagnum, or western coastal forest vegetation in maritime fringe environments, on some sites at high elevations inland, and in peaty depressions. Under virgin conditions Humic Podzols usually have thick L, F, and H or O horizons underlain by a light-colored eluvial horizon (Ae), an eluvial horizon darkened by humic material, or by a podzolic B horizon, which is usually a Bh. The B horizon may include several kinds of podzolic B subhorizons: Bh, Bhf, and Bf, which may be cemented (ortstein, placic) or friable. The material below the podzolic B horizon may be cemented (duric), compact and brittle (fragipan), or friable.
Humic Podzols have a Bh horizon at least 10 cm thick that usually occurs at the top of the B horizon but may occur below other B horizons. The Bh horizon contains more than 1% organic C and less than 0.3% pyrophosphate-extractable Fe and has a ratio of organic C to pyrophosphate-extractable Fe of 20 or more.
Humic Podzols are generally strongly acid and their B horizons are usually less than 50% base saturated (neutral salt). The pH dependent CEC of the Bh horizon is usually well above 8 cmol kg-1.
Under disturbed conditions and where the Bh horizon directly underlies the organic surface layer, the Bh may be confused with an Ah horizon. The guidelines that aid in making this distinction are that more than 50% of the organic C of Bh horizons is extractable by NaOH-Na4P2O7 and more than 50% of the extractable C of Bh horizons is fulvic acid carbon. Cultivated Humic Podzols are identified by properties of the B horizon below the cultivated layer.
Distinguishing Bh from Bhf horizons may be a problem in the field. The follow
Common horizon sequence: O or LFH, Ae, Bh, Bfgj, BCgj, Cg These soils have the general properties specified for the Podzolic order and the Humic Podzol great group. They are identified by the following properties: Usually Orthic Humic Podzols have L, F, and H or O horizons and an Ae horizon. Commonly they have a Bhf or Bf horizon underlying the Bh horizons. They may have mottling that indicates gleying at any depth within the control section. Parts of the Bhf or Bf may be cemented but do not meet the requirements of an ortstein horizon. Common horizon sequence: LFH or O, Ae, Bh or Bhc, Bfc, Cgj These soils have the general properties specified for the Podzolic order and the Humic Podzol great group. They differ from Orthic Humic Podzols by having an ortstein horizon at least 3 cm thick. An ortstein horizon is a Bh, Bhf, or Bf horizon that is strongly cemented and occurs in at least one-third of the lateral extent of the pedon. The ortstein horizon is designated as Bhc, Bhfc, or Bfc depending upon its organic C and extractable Fe content. Ortstein horizons are generally reddish brown to very dark reddish brown in color. Usually Ortstein Humic Podzols have L, F, and H or O horizons and an Ae horizon. They may have mottling that indicates gleying at any depth within the control section and placic or duric horizons or a fragipan. Common horizon sequence: LFH or O, Ae, Bh, Bhfc or Bfc, BCgj, Cgj These soils have the general properties specified for the Podzolic order and the Humic Podzol great group. They differ from Orthic Humic Podzols by having a placic horizon within the control section. A placic horizon (Bhfc, Bfc, Bfgc) consists of a single thin layer that is commonly 5 mm or less in thickness, or a series of thin layers that are irregular or involute, hard, impervious, often vitreous, and dark reddish brown to black in color. These thin horizons are apparently cemented by Fe-organic complexes, hydrated Fe oxides, or a mixture of Fe and Mn oxides. The placic horizon or thin iron pan may occur in any part of the B horizon except the Bh, and commonly it extends into the BC horizon. Placic Humic Podzols usually have L, F, and H or O horizons and an Ae horizon. They do not have an ortstein horizon but may have a duric horizon or a fragipan. Evidence of gleying in the form of dull colors or mottling Is commonly apparent especially above depressions in the placic horizon. These soils occur most commonly in wet sites in maritime regions; frequently the surface is peaty. Common horizon sequence: LFH or O, Ae, Bh, Bhf, BCc, Cgj These soils have the general properties specified for the Podzolic order and the Humic Podzol great group. They differ from Orthic Humic Podzols by having a duric horizon within the control section. A duric horizon is a strongly cemented horizon that does not satisfy the criteria of a podzolic B horizon. It usually has an abrupt upper boundary to an overlying podzolic B horizon and a diffuse lower boundary at least 50 cm below. Cementation is usually strongest near the upper boundary, which occurs commonly at a depth of 40-80 cm from the mineral surface. Usually the color of a duric horizon differs little from that of the parent material, and the structure is usually massive or very coarse platy. Moist clods at least 3 cm thick usually cannot be broken in the hands. Air-dry clods of the material do not slake when immersed in water. Some duric horizons may meet the requirements of a Bt horizon (Btc). Duric Humic Podzols usually have L, F and H or O horizons. They have neither an ortstein nor a placic horizon but may have mottles that indicate gleying in some part of the control section. Common horizon sequence: LFH or O, Ae, Bh, Bf, BCxgj, Cgj These soils have the general properties specified for the Podzolic order and the Humic Podzol great group. They differ from Orthic Humic Podzols by having a fragipan within the control section. A fragipan (Bx or BCx) is a subsurface horizon of high bulk density that has firm and brittle consistence when moist and hard to extremely hard consistence when dry. Usually it is of medium texture. Commonly it has bleached fracture planes separating very coarse prismatic units and the secondary structure is platy. Usually the fragipan is similar in color to the parent material, but it differs in structure and consistence and sometimes in bulk density. The upper boundary of a fragipan is usually either abrupt or clear, but the lower boundary is usually diffuse. Commonly it is necessary to dig to about 3 m to expose clearly the material beneath the lower boundary of the fragipan. Air-dry clods of fragipans slake in water. A fragipan may have clay skins and meet the limits of a Bt horizon (Btx). Fragic Humic Podzols usually have L, F, and H or O horizons and an Ae horizon. They do not have ortstein, placic, or duric horizons but may have mottles that indicate gleying at some depth within the control section.Orthic Humic Podzol (O.HP)
Ortstein Humic Podzol (OT.HP)
Placic Humic Podzol (P.HP)
Duric Humic Podzol (DU.HP)
Fragic Humic Podzol (FR.HP)
Note: Diagnostic horizons are underlined.