Contribution to the knowledge of a solonetsic, magnesium-rich alluvial silty clay in the Maro-Koembe plain.

Abstract

Soil survey and analysis of several profiles showed that the alluvial sediment was in an early stage of soil formation. Chemical analysis showed that it would eventually become a natraqualf. Studies of cation-exchange characteristics and of the soil solution suggested that Ca²⁺was removed more intensively than Mg²⁺ from the surface layer. However, Mg²⁺ was released strongly by weathering of minerals, but before being released into solution it was adsorbed so that there was high Mg-saturation of the exchange complex. A distribution coefficient of 1.2 for the Ca/Mg exchange equilibrium would be expected but a higher coefficient (1.4) in the A horizons of the most strongly leached soils was probably due to organic matter; a lower coefficient (1.0) in the deeper horizons was due to the mechanism of Mg release described above. Distribution coefficients for Ca/Na and Mg/Na exchange equilibria were 1.8 (Gapon) and 1.3 (Vanselow or Heald et al). It seemed possible to forecast the changes in cation-exchange characteristics that would result from further leaching and to predict the group to which the soils would finally belong. (Abstract retrieved from CAB Abstracts by CABI’s permission)