Pedogenic differences between two adjacent basalt-derived soil profiles 1. Textural and chemical characteristics

Abstract

Eleven soil samples derived from a black vertisol (Arcadia form) and a red alfisol (Shortlands form) were investigated by means of X-ray fluorescence as well as standard soil chemical and physical analyses. The profiles developed from Jurassic basalt under identical macro-environmental conditions and were situated 35 m apart. The clay content was significantly higher in the black solum, as were cation exchange capacity and organic matter, while the proportion of secondary iron phases was markedly lower. Differences in the major element composition of the soil fractions as a whole occurred with profile development, with gains in Si concomitant with a depletion of particularly Fe, Mg, Na and Ca. Gains and losses within each profile were most obvious between the two saprolite horizons and at the saprolite/solum boundary. Only small variations occurred within the solums. Trends in the major element composition of the clay fractions with decreasing depth consisted of a linear accumulation of Al and loss of Mg and Si; these were more pronounced in the red solum. Differences in element proportions between the two profiles correlated with parent material characteristics. The contrast in pedochemical development is explicable predominantly in terms of bedrock contours and related lateral movement characteristics of soil solutions and/or clay minerals. The influx of detritus was significant. © 1993 Taylor and Francis Group, LLC.