IMPACT OF TOPOSEQUENCE ON SOIL PROPERTIES AND CLASSIFICATION IN ZARIA, KADUNA STATE, NORTHERN GUINEA SAVANNA, NIGERIA

Topography plays major role in variation of soil properties and nutrient distribution along a non-uniform agricultural landscape. As a result of this, there is a need for sound soil variability knowledge for sustainable agricultural production especially in farmlands with different slope classes. This study aim at assessing the influence of topography on soil properties and classification on a toposequence in Gabari, Zaria. Four pedons were dug across the physiographic positions (crest, upper, middle and valley bottom), soil samples collected from genetic horizon of the pedons were analyzed using standard procedures. The soil colour varies from dark yellowish brown, strong brown to yellowish brown. Sand-dominated the mineral fraction with valley bottom recording highest value (61%). Clay content increases with depth except in the valley bottom. The soils were slightly acidic to neutral in reaction (6.5 – 6.9), organic carbon (3.1-4.4 g/kg), total nitrogen (0.1-0.2 g/kg) and available phosphorus (1.9 - 4.14 mg/kg) were rated low. The soils have moderately inherent natural fertility with moderately exchangeable basic cations (Ca, Mg, K, and Na). Cation exchange capacity (7.3 – 9.7 cmol (+) kg-1) was moderate while the base saturation (55-79%) suggests the soil to be fertile being >50%. Among all the soil properties, sand, silt, available phosphorus and exchangeable acidity were significantly (p>0.05) different across the toposequence. Toposequence also influence the soil types (Alfisols, inceptisols and entisols) with their classification varying from Typic plinthustalf/Eutric Lixisols on the crest to Fluvaquentic Epiaquepts/Endoeutric Fluvisol on the valley bottom based on USDA Soil Taxonomy and World Reference Base 2014.