Pedological characterization, Clay Mineralogy and classification of some soils of Mikese area, Morogoro District, Tanzania

Abstract

A study was carried out in Mikese Ward, Morogoro District, with the objective to make an inventory of the soils of the area, to determine their physico-chemical and mineralogical properties and to classify them. Eight soil profiles were identified and form three major groups of soils namely, very deep, well drained, dark reddish brown to dark brown, sandy clay loams and sandy clays on the steep convex slopes; very deep, well drained, dark brown to dark red, sandy clay loams and; sandy clays on the linear slopes; and very deep, well and imperfectly drained sandy loams to sandy clay loams and sandy clays in the valley bottoms. The soils of the convex and linear slopes classified as Isohyperthermic, deep, mixed, Kanhaplic Haplustalfs and Isohyperthermic, deep, mixed Oxic Ustropepts representing a relatively advanced pedogenic development as indicated by high contents of Fe, Al and,Ti and relatively low Si/AI ratios. The soils of the valley bottoms classified as Isohyperthennic, deep, mixed, Typic Argiustolls, Isohyperthermic, deep, mixed, Typic Tropaquepts and Isohyperthermic, deep, mixed, Fluventic Ustropepts. These soils are of low to intermediate pedogenic development as indicated by the relatively lower Fe, Al and Ti contents and both high Si and AI ratios. X-ray diffraction analysis revealed that the studied soils have a mixed clay mineralogy including kaolinite and mica. Small amounts of smectite were identified in one profile with alkaline subsoil reaction. Bulk densities of surface horizons are relatively lower than those of subsoils ranging from 1.1 to I. 6 Mg/m³ in topsoils and from 1.4 to 1.9 Mg/m³ in subsoils. Total porosity ranged from 40 to 58% in surface soils and from 28 to 32 % in subsoils. Available water holding capacities of the soils are between 155 and 248 mm/m of soil. The soils have overall poor supply of N and P. The basic cations Ca⁺⁺, Mg⁺⁺ and, K⁺ are medium to high throughout the profiles. The CEC of the soils is very low with values ranging from 6 to 13 cmol(+)/kg soil). These results imply that continuous utilization of the soils for crop production without proper management will result into a drastic loss of soil fertility.

Keywords: Pedological characterization, mineralogy, soil classification, Morogoro

Tanzania J. Agric. Sc. (11)99) Vol. 2 No. 1, 7-18