| Popis: |
The cation exchange characteristics and mineralogy of six soils collected from southeast Nigeria have been investigated. Four of these soils (Uturu/Akaeze soils) are developed on fine-grained sedimentary rocks and two (Unwana and Mballa soils) on more coarse-grained sands and sandstones. The Uturu/Akaeze soils have a higher CEC and contain more exchangeable bases in both the total soil and particle size fractions separated by mechanical dispersion, not only because they contain more clay but also because interstratified minerals occur as a major component. The Unwana and Mballa soils, on the other hand, are predominantly kaolinitic. The 2–20 μm and 20–200 μm fractions of the soils, obtained after exhaustive mechanical separation, still show the presence of large amounts of clay minerals in the form of aggregated grains. Because of chemical and mineralogical differences, it is suggested that the aggregates in the 20–200 μm fractions of the Uturu/Akaeze Group soils could represent undisaggregated rock fragments inherited from parent material, whereas aggregates in the 2–20 μm fraction are interpreted as being largely pedogenic in origin. The clay mineralogy and exchangeable cations are strongly correlated in the 20–200 μm fraction, but not in the finer fractions. Differences in the exchange characteristics of clay minerals in an aggregated or non-aggregated form may be important in rationalizing the nutrient status of these soils in terms of their mineralogy. |
