Partitioning of Clay‐Sized Minerals in Coastal Plain Soils with Sandy/Loamy Boundaries

Abstract

Four soils with sandy/loamy boundaries occurring at various depths were studied with respect to distribution of clay‐sized minerals within the soil matrix. Mineralogy of coarse and fine clay was determined by horizon using x‐ray diffraction. Also, mineralogy of clay from ped interiors vs. exteriors (coatings) was determined for the Bt horizon of one soil. Mineralogical differences in coarse‐clay distribution were observed with respect to location above or below the sandy/loamy boundary. Clay above the boundary was consistently high in hydroxy‐interlayered vermiculite (HIV) and quartz, regardless of depth to the boundary. One exception was the A horizon of a Spodosol, which consisted essentially of quartz; however, the Bh horizon of this soil (above the boundary) did contain appreciable HIV. Below the boundary, the upper Bt horizon exhibited an increase in kaolinite and a sharp decrease in quartz relative to overlying E or Bh horizons. A marked decrease in HIV below the upper Bt horizon was also evident. Fine clay contained more kaolinite and less HIV and quartz than did coarse clay, and exhibited less intra‐pedon variation. Possibly HIV comprises a greater proportion of the clay residue in eluvial horizons because of the greater size of its precursor, which could be mica, and subsequent resistance to translocation. The greater abundance of HIV in ped coatings relative to ped interiors suggests that some contemporary translocation of coarser clay from HIV‐dominated eluvial horizons has occurred along major voids between peds. The d001 peak shift with heat treatment for HIV was similar for all samples, suggesting that depth and landscape position have had little influence on degree of interlayer polymerization in these soils.

Occluded Mica in Hydroxy-Interlayered Vermiculite Grains from a Highly-Weathered Soil

“…A mica precursor is consistent with the prevalence of HIV in sandy horizons (Cabrera et al, 1989;Harris et aL, 1989). Mica, as a relatively coarse-grained phyllosilicate in sediments, would likely have weathered in place during the period when colloidal components such as kaolinite eluviated to deeper zones.…”

Location of natural trace elements in silty soils using particle-size fractionation

“…The methods most commonly used are: magnetic separation (Righi and Jadault, 1988); particle-size fractionation within the clay fraction (Rouiller et al, 1984;Cabrera-Martinez et al, 1989;Ducaroir et al, 1990;Wada et al, 1991;Delvaux et al, 1992;Ducaroir and Lamy, 1995); and density fractionation (Besnard et al, 2001). However, previous work rarely sub-fractionated the silt fractions, even though these fractions are a key to understanding the relations between primary and secondary minerals in a soil (Hardy et al, 1999), especially for soils developed on silty parent material.…”

Influência de diferentes sistemas de uso e manejo na coesão, resistência ao cisalhamento e óxidos de Fe, Si E Al em solo de tabuleiro costeiro de Alagoas

“…Na figura 2, verificou-se um aumento da razão argila fina/argila total em profundidade em todos os tratamentos estudados, com valores máximos na camada de 0,4-0,8 m. O aumento desta razão da camada de 0-0,2 m para as camadas de 0,2-0,4 m e 0,4-0,8 m deveu-se à ocorrência de processos de translocação vertical de argila ao longo do perfil do solo (Floate, 1966;Cabrera-Martinez, 1989). Os maiores valores da razão argila fina/argila total na camada de 0,4-0,8 m em todos os solos estudados foram atribuídos à presença expressiva de cerosidade nas unidades estruturais desta camada, verificada na descrição do perfil do solo em campo (Silva, 2003).…”

“…A eluviação de argila dispersa dos horizontes superficiais para horizontes subsuperficiais do solo é um processo natural, denominado argiluviação (Fanning & Fanning, 1989;Cabrera-Martinez, 1989). No entanto, a migração de partículas de argila para horizontes subsuperficiais é um processo significativo em solos cultivados, graças às modificações na estrutura do solo causadas pelos sistemas de manejo, que deixam a fração argila num maior grau dispersão, em relação às condições originais do solo (Nielsen et al, 1972).…”