Physico-chemical properties of soils in a toposequence in Mokwa, Niger state, Nigeria

Soils of a toposequence in Mokwa, Niger State, Nigeria in the Southern Guinea Savannah zone were studied in the field and classified using USDA soil taxonomy and classification system. Samples from three pedons (up, middle and lower slopes) were subjected to physical and chemical analyses as described by Jackson (1968). The soils had high gravel content in the sub-surface horizons. Bulk densities ranged between 1.01 to 1.63 g/cm³ and were generally higher in the coarser-textured soils. The soils were generally sandy with the sub-surface horizon of pedon 1 (up-slope) being dominated by sandy soils. The silt/clay weathering index showed moderate weathering. The soils were slightly acidic. The exchangeable cations present in order of magnitude were calcium, magnesium, potassium and sodium. Cation exchange capacity of the soil was low. The soils were classified as Plinthic Dystrustalf (Pedon 1), Typic Plithustalf (Pedon 2) and Psammentic Alaquept (Pedon 3). The fertility status of the soils of the area was found to be dependent on the level of the soil organic matter.