clay mineralogical composition and its influence on some physico-chemical properties of selected soils of Coast region, Tanzania
2000
Mgata, E.S(Sokoine Univerity of Agriculture, Soil Science Department, Morogoro, Tanzania) | Msanya, B.M.(Sokoine Univerity of Agriculture, Soil Science Department, Morogoro, Tanzania)
A m.ineralogical study was carried out in Coast Region, Tanzania, on soils developed from different parent materials. These materials are; unconsolidated sands and gravels of Neogene age, Grey-green marls of Cretaceous age, Calcareous siltstone and sandstone of Jurassic age and migmatitic gneisses of Precambrian age (Usagaran sys¬tem). The soil clay fractions exhibit perti¬nent differences in mineralogical composi¬tion. Soils developed from migmatitic gneisses are predominantly kaolinitic with accessory amount of goethite. Kaolinite in these soils is pedogenic and is formed from feldspars and mica. Soils formed from cal¬careous siltstone and sandstone have mixed clay mineralogy including smectite, vermiculite and illite. Both smectite and vermiculite in these soils are pedogenic and are formed from mica, while illite is inherited from the parent materials. Soils developed from the grey-green marls are dominated by smectite and have some accessory amounts of kaolinite and illite; while those developed from tertiary sedi¬ments are characterized by mixed clay mineralogy including smectite, kaolinite and traces of gibbsite. The pedogenic envi¬ronment suggests that both kaolinite and smectite in these soils are not formed insitu but are inherited from transported parent materials. The clay mineralogy is clearly reflected on the cation exchange capacity, moisture retention characteristics and car¬rying capacity (n value) of these soils.
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