Pedological characterization of typical soils of Dodoma Capital City District, Tanzania: soil morphology, physico-chemical properties, classification and soil fertility trends

Journal of Annals of Advanced Agricultural Sciences, 2018; 2 (4): 59-73Pedolological characterization was done in Dodoma Capital City District, Tanzania. Three soil profiles developed from in-situ weathering of granic rocks and designated as HIS-P1, HIS- P2 and HIS-P3 were described. Fifteen samples were taken from genetic horizons and analyzed for physical and chemical characteristics. The soils were generally very deep, with varying textures. Whereas profile HIS-P2 was dominantly loamy, profiles HIS-P1 and HIS-P3 were both clayey but the latter had heavy clay type. In profile HIS-P1, clay eluviation-illuviation was a dominant pedogenic process manifested by presence of clay cutans in the subsoil. Profile HIS-P2 displayed redoximorphic features due to fluctuating water table. Shrinking and swelling, and argilli-pedoturbation were typical pedogenic processes in profile HIS-P3. Profile HIS-P1 had more developed structure (subangular blocky) followed by HIS-P3 and lastly profile HIS-P2 which was structureless massive breaking into weak subangular blocks. Whereas topsoil bulk density values of the soils were within acceptable range, subsoil BD values are likely to cause problems of root penetration particularly for deep rooted crops. Profiles HIS-P1 and HIS-P3 may present limitations to crop growth due to high pH values (> 7.5) in the subsoil which may limit availability of plant nutrients e.g. phosphorus. Organic carbon and nitrogen were generally low and very low in all profiles with most values being < 1.25% and < 0.10%, respectively. Availabe P values were low to very low (< 7 mg/kg) throughout the three profiles. Topsoil base saturation values were high (> 50%) in profiles HIS-P1 and HIS-P2 but very high throughout proflie HIS-P3 (83 - 118%). Zn and Fe levels were rated as inadequate for crop production. According to USDA Soil Taxonomy, the soils were classified as Typic Rhodustults (HIS- P1), Fluventic Dystrustepts (HIS-P2) and Chromic Calcitorrerts (HIS-P3) corresponding to Haplic Cutanic Acrisols, Haplic Cambisols and Calcic Mazic Vertisols in the WRB for Soil Resources. The three soils had different physico-chemical properties, hence the need to characterize soils before fertilizer recommendations is met