Abstract
This study was carried out in Kilombero District, Tanzania with the objective of characterizing the soils in terms of their morphology, genesis, physico-chemical properties and classification. Three pedons KISA-P1, MKU-P1 and MBA-P1 were identified within the Kilombero Valley, dug, described and sampled. Disturbed and undisturbed soil samples were taken from designated pedogenic horizons for physical and chemical analysis in the laboratory. Using both field and laboratory data soils were classified using both USDA Soil Taxonomy and World Reference Base for Soil Resources schemes of classification. Results show that the three pedons were developed under <i>Isohyperthemic</i> temperature and <i>Aquic</i> moisture regimes. All pedons were deep (100 - 120 cm). Whereas Pedons KISA-P1 and MBA-P1 had sandy clay loam topsoils overlying sandy clay subsoils, Pedon MKU-P1 had clayey texture throughout its profile depth. All pedons had low chromas of ≤ 3 and redoximorphic features in form of abundant mottles particularly in the subsoils. Topsoils of Pedons KISA-P1 and MBA-P1 had dominantly friable to very friable moist consistence while those of Pedon MKU-P1 had very firm moist consistence. Subsoil moist consistence varied from firm to extremely firm (Pedons KISA-P1 and MKU-P1) and from friable to very firm (Pedon MBA-P1). Structures were dominantly weak to moderate subangular blocky in all studied soils but some horizons were structureless single grained and massive. Soil reaction ranged from extremely acid (topsoil of MBA-P1) to mildly alkaline (subsoil of MKU-P1) with pH values of 4.44 and 6.73 respectively. Topsoil organic carbon and total nitrogen contents in the studied pedons were low (0.66 to 1.4%) and very low to low (0.08 to 0.19%) respectively. CEC<sub>soil</sub> values were rated as low to medium ranging from 8.4 to 23.8 cmol (+)/kg respectively in Pedon KISA-P1 and Pedon MKU-P1. Percent BS values varied between and within studied pedons and ranged from low < 50% to high > 50%. Studied soils manifested nutrient imbalances in respect of basic cations. On the overall, fertility of the studied soils was rated as low to medium. According to USDA Keys to Soil Taxonomy, Pedons KISA-P1 and MKU-P1 classified as <i>Inceptisols,</i> equivalent to <i>Cambisols</i> in WRB for Soil Resources whereas Pedon MBA-P1 classified as <i>Entisols</i> equivalent to <i>Fluvisols</i>. All three sites were recommended for paddy production.
Highlights
Pedological characterization is very important in providing valuable information and knowledge on soil characteristics
Pedons KISA-P1 and MBA-P1 had sandy clay loam topsoils overlying sandy clay subsoils whereas Pedon MKU-P1 had dominantly heavy clay horizons alternating with sandy clay and clay horizons
Topsoil of Pedon KISA-P1 was black while Pedons MKU-P1 and MBA-P1 had respectively grayish brown and very dark grayish brown topsoils
Summary
Pedological characterization is very important in providing valuable information and knowledge on soil characteristics. It gives clear understanding of soil genesis, morphology, classification and spatial distribution of soils in an area [1, 2]. The valley lies at the foot of the Great Escarpment of East Africa and has a total length of 250 km and a width of up to Asheri Mwamba Kalala et al.: Pedological Characterization of Some Typical Alluvial Soils of Kilombero District, Tanzania. Not much is known about soils of Kilombero Valley in sufficient detail to allow ranking of their potential for various agricultural and non-agricultural uses and for transferring of technology to other areas with similar ecological conditions in Tanzania.
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