ABSTRACTThe present study illustrates the effect of topography on soil formation and distribution on basement complex rocks of Northern Guinea Savanna of Nigeria. Six landforms were identified through the processing of satellite images namely; Tableland with very high relief, irregular plains with some moderate relief, smooth plains with some moderate relief, flat or nearly flat plains, irregular plains with low relief and the flood plains. The associated soil units on these plains were units KB1, KB2, KB3, KB4, KB5, and KB6. Soils of KB1 were associated with the Tableland, KB2, KB3, KB4 and KB5 were associated with the undulating plains and KB6 with the flood plains. A total of 46 samples were collected from 12 profile pits across the soil units except for soil unit KB1 which were skeletal dominated with rock outcrops and shallow soils. The Tablelands were very shallow soils, undulating plains were very deep (Ë�’ 150 cm) while the flood plains were deep soils. The soils of the undulating plains were imperfectly drained to well drained with a surface soil colour ranging from very dark grey (10YR 3/1) to dark yellowish brown (10YR 3/4) while the flood plain was very poorly drained as evidenced by dark yellowish brown (10YR 4/4) to dark grey brown (10YR 4/2) surface soil colour. Blocky structure was dominant within the undulating plains while the soils of KB6 were predominantly structureless. The dominant particle size fraction across all soil units was clay at both surface and sub-surface. Bulk density was low, less than 1.85 g/cm3 at surface of all soil units. The pH was rated slightly acidic to moderately acidic in water (5.60 to 6.50) and strong acidic in CaCl2 (5.1 to 5.50), across the surface of all soil unit. Exchangeable acidity values at both surface and sub-surface across the soil units were low (0.01 to 0.20 dSm). Ca was medium to high (1.3 to 8.00 cmol(+) kg-1), Na was medium to high (0.15 to 0.60 cmol(+) kg-1) and Mg were low to medium (0.06 to 0.68 cmol(+) kg-1) while K was low (0.03 to 0.15 cmol(+) kg-1) for the surface of the undulating plains. For the flood plain, Ca was medium (3.20 to 4.76 cmol(+) kg-1) Na was high (0.45 to 0.60 cmol(+) kg-1), Mg and K were medium (0.51 to 0.59 and 0.25 to 0.30 cmol(+) kg-1 respectively). Generally the basic cations were higher in the flood plain than the undulating plains. Organic carbon and total nitrogen were all low less than (10 g/kg) and 1.5 g/kg respectively across soil units while available phosphorous was low to medium (3.15 to 16.80 mg/kg) across all soil units but generally, they were all higher in the flood plains than the undulating plains. The base saturation was generally high (Ë�’ 50% NH4AOc and Ë�’70% ECEC) across all soil units. According to the USDA/FAO classification, the soils of unit KB1 were classified as Typic Ustorthens/Regosols, KB2 p2, p3 were classified as Typic Plinthustalfs/Eutric plinthosols, KB2 p1, p4, KB3 p2, KB4 p1 and KB5 were classified as Typic Ustipsammers/Eutric Arenosols, KB3 p1 was classified as Typic Epiaqualfs/Gleyic Gleysols, and that of KB4 p2 was classified as Typic Haplustalfs/Vetic Lixisols, while those of unit KB6 were classified as Typic Epiaquepts/Stagnic Stagnosols. The undulating plains were more promising landforms than the other landforms for agricultural production, on the other hand the Tableland with very high relief are least promising for agricultural production
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