Petrocalcic Horizon
Encyclopedia
A petrocalcic horizon is a diagnostic horizon in USDA soil taxonomy
. They are formed when secondary Calcium Carbonate
or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan
. Petrocalcic horizons are similar to a duripan
and a petrogypsic horizon in how they affect land-use limitations. They can occur in conjunction with duripans where the conditions are right and there are enough free carbonates in the soil. Calcium Carbonates are found in alkaline soils, which are typical of arid and semiarid climates. A common field test for the presence of carbonates is application of hydrochloric acid
to the soil, which indicates by fizzing and bubbling the presence of calcium carbonates.
, tenth edition, 2006" are:
1. The horizon is cemented or indurated by carbonates, with or without silica or other cementing agents; and
2. Because of lateral continuity, roots can penetrate only along vertical fractures with a horizontal spacing of 10 cm or more; and
3. The horizon has a thickness of:
a. 10cm or more or
b. 1cm or more if it consists of a laminar cap directly underlain by bedrock.
age. They form in soil parent material
that contains calcium carbonate
or receive regular inputs of carbonates through dust. Carbonates are transported into the subsoil by water that precipitates the carbonates in the subsoil upon evaporation, eventually forming a massive, continuous layer of cemented carbonates. There is also some evidence that petrocalcic horizons can form "in situ" by alteration of limestone
parent materials and alternating dissolution/precipitation of calium carbonates.
Duripan
Fragipan
Petrogypsic horizon
Hardpan
More information on soils in specific areas of the United States can be found on Web Soil Survey at: http://websoilsurvey.nrcs.usda.gov/app/
USDA soil taxonomy
USDA Soil Taxonomy developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.- Example of...
. They are formed when secondary Calcium Carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
or other carbonates accumulate in the subsoil to the extent that the soil becomes cemented into a hardpan
Hardpan
In soil science, agriculture and gardening, hardpan or ouklip is a general term for a dense layer of soil, usually found below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water...
. Petrocalcic horizons are similar to a duripan
Duripan
A duripan is a diagnostic soil horizon of the USDA soil taxonomy that is cemented by illuvial silica into a subsurface hardpan. Similar to a fragipan, petrocalcic horizon and petrogypsic horizon, it is firmly cemented and restricts soil management. In soil descriptions, they are most often denoted...
and a petrogypsic horizon in how they affect land-use limitations. They can occur in conjunction with duripans where the conditions are right and there are enough free carbonates in the soil. Calcium Carbonates are found in alkaline soils, which are typical of arid and semiarid climates. A common field test for the presence of carbonates is application of hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
to the soil, which indicates by fizzing and bubbling the presence of calcium carbonates.
Characteristics
The Required Characteristics of a petrocalcic horizon according to the "Keys to USDA soil taxonomyUSDA soil taxonomy
USDA Soil Taxonomy developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.- Example of...
, tenth edition, 2006" are:
1. The horizon is cemented or indurated by carbonates, with or without silica or other cementing agents; and
2. Because of lateral continuity, roots can penetrate only along vertical fractures with a horizontal spacing of 10 cm or more; and
3. The horizon has a thickness of:
a. 10cm or more or
b. 1cm or more if it consists of a laminar cap directly underlain by bedrock.
Genesis
Petrocalcic horizons are typically found in older soils and are considered a mark of advanced soil evolution. Most petrocalcic formed before the HoloceneHolocene
The Holocene is a geological epoch which began at the end of the Pleistocene and continues to the present. The Holocene is part of the Quaternary period. Its name comes from the Greek words and , meaning "entirely recent"...
age. They form in soil parent material
Parent material
In soil science, parent material is the underlying geological material in which soil horizons form...
that contains calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
or receive regular inputs of carbonates through dust. Carbonates are transported into the subsoil by water that precipitates the carbonates in the subsoil upon evaporation, eventually forming a massive, continuous layer of cemented carbonates. There is also some evidence that petrocalcic horizons can form "in situ" by alteration of limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
parent materials and alternating dissolution/precipitation of calium carbonates.
See also
USDA soil taxonomyUSDA soil taxonomy
USDA Soil Taxonomy developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Suborder, Great Group, Subgroup, Family, and Series.- Example of...
Duripan
Duripan
A duripan is a diagnostic soil horizon of the USDA soil taxonomy that is cemented by illuvial silica into a subsurface hardpan. Similar to a fragipan, petrocalcic horizon and petrogypsic horizon, it is firmly cemented and restricts soil management. In soil descriptions, they are most often denoted...
Fragipan
Fragipan
A fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations...
Petrogypsic horizon
Hardpan
Hardpan
In soil science, agriculture and gardening, hardpan or ouklip is a general term for a dense layer of soil, usually found below the uppermost topsoil layer. There are different types of hardpan, all sharing the general characteristic of being a distinct soil layer that is largely impervious to water...
More information on soils in specific areas of the United States can be found on Web Soil Survey at: http://websoilsurvey.nrcs.usda.gov/app/