Particle size and free iron oxide distribution in some latosols and groundwater laterites of Ghana

Abstract

The distribution of particle size and Na-dithionite-extractable (di-Fe 2 O 3) and NH 4-oxalate-extractable (ox-Fe 2O 3) iron oxides were investigated in twelve soil profiles representing latosols and groundwater laterites. Soil profiles studied were selected from the major ecological zones of Ghana. The pattern of distribution of free Fe 2O 3 was closely related to that of clay (< 2 μ) in soil profiles of the humid forest zones where clay content was more than 40% in the B horizons. In soil profiles of the relatively dry savannah zones with less than 40% clay in the B horizon, the pattern of distribution of free Fe 2O 3 was closely related to that of silt (2–20 μ). The amount of free Fe 2O 3 in the soils appeared to be related to kind of parent rock or parent material and to climatic factors operating in the various ecological zones. Using the amount of di-Fe 2O 3 in the B horizon as a basis for assessing the relative degrees of pedogenesis in soil profiles developed from the same kind of parent material, it was concluded that soil profile development had progressed most in the rain forest zone. Free Fe 2O 3 was considered as having reached an advanced stage of crystallinity or aging in most of the soils because of the low ox-Fe 2O 3/di-Fe 2O 3 ratios in the solums of most of the soil profiles. Soils studied were placed in the ferrallitic and ferruginous soil classes of D'Hoore. The great soil groups could not be characterized by depth function curves of free Fe 2O 3. However, it was proposed that the relative amounts of di-Fe 2O 3 in the B horizons of the soil profiles could be used as a basis for classifying these soils at the family level.