The particle-size distribution and mineralogical composition of the clay （〈 2 μm） and fine-sand （0.25-0.10 mm） fractions in soils of two inland valleys in Abakaliki and Bende, Southeast Nigeria, were investigate...The particle-size distribution and mineralogical composition of the clay （〈 2 μm） and fine-sand （0.25-0.10 mm） fractions in soils of two inland valleys in Abakaliki and Bende, Southeast Nigeria, were investigated to provide basic information on soil-forming processes and agricultural potentials. These soils were silty or clayey, deriving from Cretaceous or Tertiary shale materials. The particle-size distribution and its computation on a clay-free basis revealed relatively remarkable lithologic breaks in a couple of pedons. The effect of lithologic discontinuities on soil mineralogical composition was not, however, conspicuous. Petrographic investigation revealed that quartz predominantly comprised the fine-sand fraction in the soils at both study sites. Nevertheless, the clay mineralogical composition of the soils was a mixture of kaolinite, irregularly interstratified smectite-illite intergrades （S/I）, hydroxyl-A1 interlayered 2：1 type clays （HICs）, vermiculite, smectite, halloysite and illite along with fine-sized quartz in Abakaliki. The soils of Bende predominantly contained smectite, which was partially interlayered with hydroxyl-A1 and kaolinite. It is suggested that seasonal floodwater has slowed the disintegration of weatherable clay minerals inherited from the shale, while quartz originating from the sandstone is predominant in the fine-sand fraction. Additionally, a possible soil-forming process observed at the both study sites was ferrolysis, which was indicated by a clear decreasing pattern of HICs downward in the soil profiles, The entry of S/I and vertical distribution patterns for a couple of clay minerals in the pedon suggested that the soils in Abakaliki have developed under the significant influence of aeolian dust delivered by the Harmattan. The findings might describe a site-specific deposition pattern of Harmattan dusts as well as hydromorphic soil-forming processes in the wetlands of the inland valleys.展开更多
Sodic soils are typically located in semi-arid to arid climates. However, sodic soils in continental humid climates are rare. As with sodic soils in dry climates, sodic soils in wetlands pose management difficulties f...Sodic soils are typically located in semi-arid to arid climates. However, sodic soils in continental humid climates are rare. As with sodic soils in dry climates, sodic soils in wetlands pose management difficulties for agriculture, forestry, or wild-life habitat. The typical practice of gypsum application is problematic given inability to provide drainage. Natraqualfs located in southeastern Missouri present an acid argillic horizon superimposed on a natric horizon, where the exchangeable sodium percentage and an alkaline reaction are characteristic attributes. Ferrolysis is an active soil process that is slowly degrading the natric horizon because of exchangeable Al<sup>3+</sup> and H<sup>+</sup> generation and re-stabilization of the soil structure, permitting leaching of the sodium.展开更多
基金Project supported by the Grant-in-Aid of Japan Society for the Promotion of Science, Ministry of Education, Culture,Sports, Science and Technology (Nos. 15101002 and 19002001)
文摘The particle-size distribution and mineralogical composition of the clay （〈 2 μm） and fine-sand （0.25-0.10 mm） fractions in soils of two inland valleys in Abakaliki and Bende, Southeast Nigeria, were investigated to provide basic information on soil-forming processes and agricultural potentials. These soils were silty or clayey, deriving from Cretaceous or Tertiary shale materials. The particle-size distribution and its computation on a clay-free basis revealed relatively remarkable lithologic breaks in a couple of pedons. The effect of lithologic discontinuities on soil mineralogical composition was not, however, conspicuous. Petrographic investigation revealed that quartz predominantly comprised the fine-sand fraction in the soils at both study sites. Nevertheless, the clay mineralogical composition of the soils was a mixture of kaolinite, irregularly interstratified smectite-illite intergrades （S/I）, hydroxyl-A1 interlayered 2：1 type clays （HICs）, vermiculite, smectite, halloysite and illite along with fine-sized quartz in Abakaliki. The soils of Bende predominantly contained smectite, which was partially interlayered with hydroxyl-A1 and kaolinite. It is suggested that seasonal floodwater has slowed the disintegration of weatherable clay minerals inherited from the shale, while quartz originating from the sandstone is predominant in the fine-sand fraction. Additionally, a possible soil-forming process observed at the both study sites was ferrolysis, which was indicated by a clear decreasing pattern of HICs downward in the soil profiles, The entry of S/I and vertical distribution patterns for a couple of clay minerals in the pedon suggested that the soils in Abakaliki have developed under the significant influence of aeolian dust delivered by the Harmattan. The findings might describe a site-specific deposition pattern of Harmattan dusts as well as hydromorphic soil-forming processes in the wetlands of the inland valleys.
文摘Sodic soils are typically located in semi-arid to arid climates. However, sodic soils in continental humid climates are rare. As with sodic soils in dry climates, sodic soils in wetlands pose management difficulties for agriculture, forestry, or wild-life habitat. The typical practice of gypsum application is problematic given inability to provide drainage. Natraqualfs located in southeastern Missouri present an acid argillic horizon superimposed on a natric horizon, where the exchangeable sodium percentage and an alkaline reaction are characteristic attributes. Ferrolysis is an active soil process that is slowly degrading the natric horizon because of exchangeable Al<sup>3+</sup> and H<sup>+</sup> generation and re-stabilization of the soil structure, permitting leaching of the sodium.
