Inceptisols are immature soils of humid and subhumid regions that have altered horizons with evidence of chemical and physical change, but still have some weatherable material and lack a clear illuviated
zone (Figure 3-12).
2010) have reported illuviation features (argillans or illuviated
clay cutans) in cohesive soils from different parts of Brazil (Pernambuco and Alagoas), their presence has either not been recognised in many soils or has been observed in small quantities (Melo and Santos 1996; Lima et al.
Soil profiles of the inter-dune depressions show an accumulation of organic matter in the predominantly sandy A1 horizon and a bleached A2 horizon over a dense illuviated organic B horizon of sandy loam.
It is suggested that the flooded conditions at the time may have raised levels of dissolved organic carbon in surface soil from illuviated humus sources in the subsoils of these podzols.
These are subsurface accumulation horizons of organic matter, illuviated from the surface horizons in the form of chelates with a variable content of oxides of iron and of aluminum.
Below this, there is a Bh horizon (79-102 in [200-260 cm] thick) that is dark brown to black and the result of the accumulation of illuviated organic matter, which covers the sand grains and may cement them together.
It is possible that smectite was deposited on the dunes as a minor constituent of aeolian dust, which subsequently disaggregated, and because of the generally very small size of smectite particles (Pye and Sherwin 1999) these were preferentially illuviated
from the upper phases of the dunes.
In other cases, after the washing of the carbonates, the clay may have been illuviated
to form an argillic horizon--one of considerable thickness but containing only a little clay.
It indicated that illuviated
iron was not the main resource of iron oxides in iron nodules, Free Fe-oxide ([Fe.sub.d]) contents in the iron nodules are always higher than those of soil matrices, but the [Fe.sub.o]/[Fe.sub.d] ratio in iron nodules was very low (Table 3).
As a result, the particles in the surface horizon are dispersed and illuviated
deeper into the soil, a process favored in spring by the reversal of the thermal gradient.
The purpose of this investigation was to study this process according to land use and to compute the amount of organic carbon in the subsoil as a consequence of illuviated
ped coating in the subsoil.
The result is the formation of horizons of accumulated illuviated
clays which are called argillic endopedons.