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Morphogenesis and erodibility of soil‐saprolite complexes from magmatic rocks in Swaziland (Southern Africa)
Author(s) -
Scholten Thomas,
FelixHenningsen Peter,
Mushala Hezekiel M.
Publication year - 1995
Publication title -
zeitschrift für pflanzenernährung und bodenkunde
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 87
eISSN - 1522-2624
pISSN - 0044-3263
DOI - 10.1002/jpln.19951580207
Subject(s) - saprolite , weathering , pedogenesis , geology , soil water , geochemistry , organic matter , topsoil , erosion , parent rock , leaching (pedology) , soil science , geomorphology , chemistry , organic chemistry
The Kingdom of Swaziland in Southern Africa is affected by diverse forms of severe soil erosion as a consequence of population growth, deforestation, and overgrazing of the grass savanna. The physical, chemical and mineralogical properties of soil‐saprolite complexes show that the presence of relict saprolite underlying the soils is an essential precondition for the development and rapid expansion of deep incising erosion gullies in areas with magmatic rocks. The polygenetic isovolumetric weathering of saprolite led to mass losses of more than 50 vol.‐% due to the formation of solution cavities by leaching in warm and humid climatic phases. Therefore, the saprolite is highly susceptible to erosion. Low structure stability of the saprolite, indicated by shear strength values < 5 kPa, results from a silty texture, absence of organic matter, and low contents of Fe‐ and Al‐oxides and exchangeable Al‐ions. On the contrary, the clay‐rich ferrallitic soils developed from saprolite are comparatively stable against erosion. The relatively high structure stability of the soil, indicated by shear strength values ranging from 7 to 12 kPa, results from the organic matter content of about 3 wt.‐% C org in the topsoil, up to 7 wt.‐% pedogenic Fe‐ and Al‐oxides, pH(KCI)‐values around 4, and Al‐saturations above 50 %. Concerning the genesis and the susceptibility to erosion, the results show a distinct bipartition of the weathering mantle. Therefore, it is necessary to investigate the site properties and spatial distribution of complete soil‐saprolite complexes from magmatic rocks as a basis of soil erosion control, land evaluation, and land use planning.