Depletion features


Son zonas en las que se ha producido el .

These are zones in which leaching of Fe/Mn took place.

They form nodules and hypo-coatings and correspond to mottles with low chromes described in the field.



It are bleached zones with pale colors, sometimes yellowish but frequently grayish, which are the result of reduction and mobilization of Fe++ and Mn++, followed by their leaching and accumulation below the reduced zone.

They alternate with areas of more intense red, brown or yellow colors in which oxidized Fe and Mn occur.

Such horizons are universally referred as "with mottles of low chroma <2" and point to hydromorphism.

These mottled horizons coincide with the zones of fluctuation of the water table or the groundwater level.

The discolorations are referred to as nodules and domains or mottles when they appear as punctual, more or less isolated zones, and hypo- or quasi- coatings when they are associated to the surface of peds or macropores.

When only Fe and/or Mn are lost, they are considered as Fe/Mn deficient hypo-coatings, if also clay is leached, it are textural hypo-coatings with a clay, Fe and Mn depletion.

Fe-depleted hypo-coatings can artificially be produced by attacking Mn and/or Fe nodules with hydrochloric acid


Hydromorphic conditions

Depending upon the intensity and frequency of the discolorations, the bleached nodules and mottles represent different degrees of hydromorphism.

Both the Fe/Mn and the clay depleted hypo-coatings are features related to relative intense hydromorphism.

They are formed by the circulation of strongly reducing solutions in the macropores through the horizon. These macropores contain plant roots which supply sufficient organic material to create a clearly reducing environment. Infiltrating through the aggregate, the water will reduce Fe and Mn, which get mobilized in this superficial zone, producing a more or less thin hypo-coating which will progressively extend to the center of the aggregate. Mn is generally, and Fe sometimes, eliminated from the profile, but frequently part of the Fe is oxidized in the interior of the aggregates, as a consequence of the existence of a more oxidizing environment, forming quasi-coatings separated from the surface of the aggregates by a hypo-coating deficient in Fe or Fe and clay.

Nowadays it seems accepted that a total saturation with water is not absolutely indispensable for the formation of mottles with low chroma, but that it is sufficient that the soil remains permanently moist (but without reaching the total saturation) during a long time, with a pronounced reducing environment in the intrapedal micropores.



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