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Soil genesis, phosphorus and micronutrients of selected Vertisols and associated Alfisols of northern Cameroon
An integrated soil genesis, phosphorus and micronutrient (Fe, Mn, Cu, Zn) study was conducted for seven northern Cameroon Vertisols and associated Alfisols. Vertisols developed from Precambrian schist are classified as Entic Pellusterts. Similar soils developed from Quaternary lacustrine and fluvial sediments are classified as Typic or Entic Pellusterts and Entic Chromusterts. The Alfisol is developed from Precambrian granite and is classified as an Arenic Haplustalf. All soils are developed under an isohyperthemic temperature regime (mean annual temperature, 27° to 30°C) and an ustic soil moisture regime (mean annual rainfall, 600 to 900 mm). Those developed on nearly level fluvial plains are seasonally flooded. All Vertisols crack to the surface but lack gilgai microrelief. They are dominantly dark gray to grayish brown. All soils are very compact and dense (1/3 bar bulk density, 1 to 1.6 g/cm³). Clay contents generally exceed 40% in the control section. Organic carbon is low (<1.27%) and decreases with depth. Base status is high and dominated by Ca and Mg on the exchange complex; pH ranges from 5.6 to 8.3. Sand and silt mineralogy is dominated by quartz, plagioclase and K-feldspars for soils of lacustrine origin. In addition, soils derived from schists contain calcite, mica, hydrobiotite, vermiculite, chlorite, smectite, amphiboles and kaolinite. Clay mineralogy for soils of lacustrine origin is smectite, kaolinite, vermiculite and mica. In addition for soils of schist origin, chlorite and hydrobiotite occur. Microfabrics are dominantly masepic and vo-skel-masepic for lacustrine soils. They are largely argillasepic for soils of schist origin. Elemental analyses of sand and silt fractions indicate high nutrient reserves. Micronutrient availability in the seasonally flooded soils is controlled by oxidation and reduction reactions. In schist soils, high pH and reactive carbonate surfaces are the controlling factors. Adequate micronutrient levels exist for Fe, Mn and Cu, but Zn is low. Extractable and organic P are low for all soils. Phosphorus sorption is largely controlled by clay, amorphous Al and Fe, and organic carbon. The Freundlich and Langmuir equations constitute useful tools for predicting P sorption parameters. Forest regeneration in northern Cameroon is constrained by low moisture status and adverse soil physical properties. Selection of adaptable tree species and use of profile modification and conservation practices will enhance the forest regeneration efforts.
Ph. D. in Soil Science Texas A & M University 1986
Includes bibliographical references (leaves 246-271).