SILICATE AND IRON OXIDE MINERALOGY OF MAJOR SOILS OF SOUTHERN INDIANA

WANDERLEY ANTONIO TREMOCOLDI, Purdue University

Abstract

For this study sites were sampled in a west-east transect from Knox County to Washington County, Indiana. This transect was designed to cross modern soils developed over different thickness of loess, and immediately underlying paleosols developed from different parent material. The objectives are to determine the differences in slicate and iron mineralogy, if any, (1) among the loess derived B horizons of modern soils along a loess-thinning transect, (2) between modern Bt horizons and paleosol Btb horizons, (3) between fragipans and other horizons in the same soil, (4) among the paleosols derived from various parent materials and especially between red B horizons of paleosols over limestone and brown B horizons of paleosols over clastic rocks. In the Bt horizons of the loess-derived soils, as loess thins kaolinite content increased, and illite and montmorillonite contents decreased, probably because of the greater development of the soil. Chemically, Al(,d) and Fe(,d) showed some tendency toward increase with loess-thinning. Paleosols show evidence of greater soil development than modern soils. Paleosol Btb horizons have higher kaolinite and vermiculite and lower montmorillonite and illite contents than modern B horizons. Fragipan horizons have higher montmorillonite contents and greater surface areas than the respective Bt horizons of the modern soils and the Btb horizons of paleosols. They also have higher extractable Si (by CBD) of the whole clay (< 2 (mu)m) and whole soil (< 2mm) and lowest extractable Al of the whole soil than the respective Bt and Btb horizons. The silicate clay mineralogy is qualitatively the same and quantitatively very similar among paleosols of different parent materials. All B horizons contain goethite, but only the Btb and Bt horizons of the reddish Crider soil (over limestone) contain hematite. It is suggested that the presence of hematite is related to the limestone, which favors better drainage of the profile and maintains higher pH and Ca('2+) levels in the soil where Fe minerals form.

Degree

Ph.D.

Subject Area

Agronomy

COinS