An assessment of morphological, physical, chemical, and mineralogical properties of soils derived from volcanic deposits in Rwanda

Volcanic deposits in the northwestern region of Rwanda originated from eruptions of six volcanos situated along the Rwandan border with Zaire and Uganda. The objectives of this study were to assess soil properties at different elevations and among soils developed from volcanic materials differing in petrological composition and age, and to compare soils under the native vegetation to those under cultivation. The soils are characterized by thick, dark A horizons and dark brown or grayish brown cambic horizons. Organic C is high and is associated with high sodium pyrophosphate extractable aluminum and iron. Phosphate retention is high and varied according to sodium pyrophosphate extractable aluminum and allophane contents. Soil cation exchange capacity, organic C, water retention properties, and aluminum and iron associated with organic matter and allophane decrease whereas, pH and bulk density increase with elevation. Allophane content decreases whereas, halloysite increases with decreasing elevation. Variations in soil properties with elevation reflect differences in clay mineralogical composition. Variations in physical and chemical properties of soils developed from different parent materials may be caused, in part, by differences in cropping history. Differences in clay mineralogy between soils developed from different parent materials exist but do not reflet differences in the age of the parent materials. Cultivated soils have higher bulk density and lower water retention properties than do undisturbed soils.U of I OnlyETDs are only available to UIUC Users without author permissio