Effect of soil depth and topography on physical and chemical properties of soil along federal college of forestry, Ibadan North West, Oyo State

Abstract

Soil properties along a toposequence is a key to sustainable crop and soil productivity, hence the need to study the effect of toposequence and soil depth on physical and chemical properties of soil around Federal College of Forestry, Ibadan, Oyo-State. Four profile pits were dug along the toposequence in Federal College of Forestry, Ibadan, Oyo-State. Soil samples were collected from three soil depth (0 - 30 cm, 30 - 45 cm, and 45 - 60cm) from four profile pits that was dug along the toposequence, (crest, sedentary, middle and valley bottom) for analysis of physical, morphological and chemical properties following standard procedures at the laboratory. The results showed that the consistency of the soil in profile pit 1 (crest) is slightly sticky and slightly plastic compared to soil in profile pit 2 (sedentary) that is predominantly nonplastic while profile pit 3 and 4, (middle/creep and valley bottom) are non-plastic, non-sticky, slightly sticky. The highest total porosity values was recorded at the valley bottom of the forest (57.74 %), followed by middle of the forest (53.21 %) while the least was by crest of the forest (51.7 %). The highest saturated hydraulic conductivity was recorded at the crest of the forest (15.91 cm hr^-1) and the least by valley bottom of the forest (8.44 cm hr^-1). Likewise bulk density values at the crest of the forest (1.28 g cm^-3) was the highest compared to valley bottom of the forest (1.12 g cm^-3). The highest (52 mg kg^-1) and the lowest (1 mg kg^-1) available P values were recorded at the valley bottom layers of the forest land soils and sedentary of the forest land soils, respectively. The highest exchangeable Ca was found in the valley bottom of forest soils (4.44 cmol kg^-1) at the upper topographic position, whilst the lowest values were recorded at the crest layers of forest soils (1.2 cmol kg^-1) at the middle topographic positions. Thus, it was concluded that the soils position on the topography affects the composition of the soil at each sampling point. This indicated that landscape in the study area affects the process of soil formation. Therefore, integrated soil fertility management and soil conservation measures are required in all topographic positions to maintain soil physicochemical properties.

Key words: Toposequence, soil profile, physical properties, chemical properties