ClasSoil Genesis in Volcanic Areas of the Jos Plateau, Nigeria.sification of soils planted with orange (citrus sinensis) and mango (mangifera indica) in the Nigerian guinea savanna
The purpose of this study was to explain the genesis of soils formed in the volcanic areas of the Jos Plateau, Nigeria. Ten soil profile pits, representing the various landscape segments of a typical volcano and a lava plain, were dug, described and sampled for physical, chemical and mineralogical analyses. The results show early, moderate and advanced stages of soil development on the cones, upper / middle footslopes and toeslopes, respectively, indicating that soil maturity stage increases from the crest down to the toeslopes. Amorphous clay minerals are found in the young soils while kaolinite dominates the clay fraction in the mature ones. Similarly, soil pH, organic carbon, exchangeable bases and CEC decrease as soil maturity increases. The important soil forming processes in the study area include addition of organic matter, clay formation from hydrolytic weathering, soil structure formation, clay migration (eluviation and illuviation), acidification, loss of basic cations through leaching, gleying, ferralization and allitization. The major weathering process is that of hydrolytic weathering of the pyroclastic materials, including basaltic rocks, pumice, lava and ash. Soil erosion and aeolian sedimentation have affected the soils. Intensive weathering and leaching precluded the formation of 2:1 clay minerals. In the same vein, because of the effects of tropical climate the soils could not meet the requirements of Andisols.
Key words: Soil genesis, Soil properties, Volcanic areas, Jos Plateau, Nigeria.