PEDOGENESIS OF A LITHOSEQUENCE IN THE NORTHERN GUINEA SAVANNA OF KADUNA STATE, NIGERIA

187

Abstract:

Lithosequence of soils developed on four basement complexes, namely Older Granites (OG), Quartzites (QZ), Mica Schists (MS) and Migmatite Gneiss (MG) was conducted on crest position in the Northern Guinea Savanna of Kaduna State, Nigeria with a view to explaining their pedogenesis. Three pedons were dug on each parent material. Soil morphological, physicochemical and mineralogical properties were examined and classified for their sustainable uses. Results indicated that soil morphological properties were generally similar, except for variation in depth and structure. The soils were generally deep to very deep (135 – 190cm), but had restrictions due to parent materials on quartzite and mica schist (QZ1, MS2 and MS3) and presence of plinthite on migmatite gneiss. Dark brown colour dominated the surface, while strong brown in subsurface horizons with wider variation in the deeper subsurface horizons (10YR, 7.5YR and 5YR). Texture of surface soil was sandy loam and was attributed to erosion and eluviation of clay resulting in textural variation with soil depth. The subsoils had clay to sandy clay with sandy clay loam in the deeper portion of the subsurface horizons. The soils were dominated by sub-angular blocky structure except soils on mica schist which had platy structure in the subsoils. Sand dominated fine earth portion of the soils (ranged between 271 and 691 gkg-1) and their subfractions were significantly influenced by parent materials and horizon differentiation. Particle density varied between 2.56 and 2.68 Mgm-3 and bulk density between 1.34 and 1.79 Mgm-3 in the soils. Water retention difference was generally slightly low and varied between 0.64 and 33.26 cm. Parent materials had significant influence on some chemical properties such as exchangeable Ca, TEB, EA, CECs, base saturation and ESP. Higher values of exchangeable Ca, TEB, EA, CECs and base saturation were in soils developed on MS followed by OG and QZ and least values were in soils on MG. These variations were attributed to leaching of bases and difference in pedogenic development (age). The chemical properties of the soils indicated strongly acid to neutral pH (5.30 – 6.90). Total exchangeable bases ranged between 2.92 and 8.98 cmol (+) kg-1, cation exchange capacity (CEC – NH4OAc) were low to high, and moderate base saturation dominated the soils. The values of organic carbon (10.00 gkg-1) and total nitrogen (1.00 gkg-1) were generally low. Micronutrients (available and total forms) were all in adequate quantity, with available Fe, Mn and total Zn significantly influenced by parent materials. Parent materials and pedogenesis significantly influenced pedogenic forms of iron oxide and crystallization was in the order of soils on mica schist < quartzites < older granite < migmatite gneiss, whereas forms of manganese oxides were significantly influenced by horizonation. Kaolinite, diaspore, muscovite and illite dominated the mineralogy of clay fraction of the soils. Nature and extent of weathering of parent materials caused variation in mineralogy of the soil and their moderate pedogenic development. Mineral composition reflected soils on migmatite gneiss as most weathered and those on mica schist as least weathered. Contents of major and trace elements (total oxide) in the soils were not significantly influenced by difference in parent material, except for K2O (P < 0.05), TiO2 and Cr2O5 (P < 0.01). Parent materials significantly influenced relative weathering intensity of most total elemental oxides, with significantly lowest relative retention mostly in soils on MG and highest in soils on MS, thus reflecting variation in their pedogenic development (age). Parent materials and pedogenic age were prominent factors that affected soil properties, thereby influenced their pedogenesis. The main pedogenic processes include weathering of parent materials, relative accumulation and depletion of major and trace elements, structural differentiation and plinthization, braunification, humification, melanization, leaching, argilluviation, desilication, allitization and ferritization. According to the USDA Soil Taxonomy, all the pedons on migmatite gneiss were classified as Typic Plinthustalf at the subgroup level. Pedons on mica schists MS1 and MS2 were classified as Typic Haplustalf, while MS3 was classified as Kanhaplic Haplustalfs. 9 Soils on quartzite were classified as Lithic Haplustalf (Pedon QZ1), Kanhaplic Haplustalf (Pedon QZ2) and Typic Kandiustalf (Pedon QZ1). Pedons on older granite were classified as Typic Kanhaplustalf (OG1), Typic Haplustalf (OG2) and Kandic Paleustalf (OG3). In the World Reference Base Classification System, all the pedons on older granite and quartzite were classified as Haplic Lixisol, whereas those on migmatite gneiss as Plinthic Lixisol. Pedons on mica schist (MS1 and MS2) were classified as Haplic Luvisols, whereas MS3 as Haplic Lixisol. Management options suggested include construction of contour ridges and bunds, and cultivation of cover crops. Effective post harvest crop residue incorporation, application of farm yard manure and incorporation of legumes in crop rotation fields, as well as use of organomineral fertilizers will sustain the soils for crop production. Fertilizer application should be timely in judicious quantity and by burying to remedy their deficiencies.

PEDOGENESIS OF A LITHOSEQUENCE IN THE NORTHERN GUINEA SAVANNA OF KADUNA STATE, NIGERIA

DOWNLOAD PROJECT