Soil Catena Research Articles

Noteworthy Features of Uruguayan Soils

AbstractUruguay has an undulating landscape dominated by Pradera (Prairie) soils with thick, black, fertile A horizons. These soils have strong textural profiles but are only moderately deep (about 80 cm average), have high base saturations, and generally have Cca horizons. There is a typical soil catena that includes the Pradera soils along with Grumosoles and Plano‐soles. This catena occurs on a variety of parent materials in various parts of Uruguay.

Two North Carolina Coastal Plain Catenas: II. Micromorphology, Composition, and Fragipan Genesis

AbstractA study of two soil catenas of different age in the middle Coastal Plain of North Carolina compares the micromorphology and composition of fragipan and nonfragipan soils. The two catenas differ principally in that one has bisequal sola and fragipans in the less well‐drained members, whereas the other has thinner sola with well‐developed argillic horizons but no fragipans. Presence of papules, as well as high packing density and proximity indices, indicate that collapse of the soil matrix has caused the high bulk density of the fragipan horizons. The relatively low amounts of clay in fragipan horizons is believed to be a result of the greater susceptibility of clay to translocation and possibly destruction during reduction and removal of the iron. Translocation of this clay is confirmed by the marked increase of illuvial clay bodies, primarily illuviation cutans and grain argillians, in B′2t horizons below the fragipan (A′2gx). Relative to their clay content, fragipan horizons contain more fine clay with infrared absorption bands in the 2.9µ H‐bonded OH region than do nonfragipan horizons. This clay lacks definite crystalline form and is thought to be amorphous. Stable at lower temperatures, the infrared absorption band at 2.9µ is lost along with the fragipan brittleness at 300C. Though of low free iron content, this clay has a high pH dependent charge. Under the low pH conditions (4.5–5.0) found in fragipan horizons, this clay may develop strong hydrogen bonds with quartz and other silicates.

Two North Carolina Coastal Plain Catenas: I. Morphology and Fragipan Development

AbstractTwo soil catenas of the Coastal Plain of North Carolina were studied. The older catena formed in feldspathic sediments and the wetter members have fragipans and bisequal profiles. The younger catena formed in quartz‐rich sediments and fragipans are absent in most soils. The younger catena has finer textured B horizons and thinner sola than comparable members of the older catena. The moderately well‐drained members of the two catenas are similar.

A soil catena on denuded laterite profiles in Queensland

A catena comprising 10 distinct zones on variously denuded laterite profiles in central Queensland is described. Red and yellow earths occur on intact or slightly stripped uplands. On denuded weathered zones, solodized solonetz, solodic, and related soils with abrupt textural differentiation have formed on intermediate slopes and saline-alkali clay soils occur on lower slopes. Soil differences are related partly to differences in parent materials and partly to the spread of weathering and erosion products across the topographic sequence. The catena either in whole or in part is repeated over wide areas. The weathering of primary minerals in parent rocks appears to be the most likely source of salts that led to the formation of halomorphic soils. The soluble materials have been leached and redistributed by surface and subsurface seepage from denuded mottled and pallid zones upslope. The clay soils appear to have formed mainly on materials derived from shales that were originally overlain by arenaceous upper Tertiary sediments, but some reworking of these materials may have occurred. Montmorillonoid clays have been preserved from deep weathering by their impermeable nature.

Field Studies of a Clay‐Enriched Horizon in the Lowest Part of the Solum of Some Brunizem and Gray‐Brown Podzolic Soils in Illinois

AbstractThe morphology, range in expression, and occurrence are described of a clay‐enriched layer (Beta horizon) found below the B2 horizon of selected soils in the area of Wisconsin glaciation in northern Illinois. The Beta horizon, characterized by a darker color and an abrupt, irregular lower boundary, was more pronounced in coarser textured drift, in Gray‐Brown Podzolic soils, and in well‐drained members of soil catenas.