DISTRIBUTION OF SOIL PHYSICOCHEMICAL PROPERTIES AND PHOSPHORUS FRACTIONS ALONG TOPOSEQUENCES IN THE SOUTHERN GUINEA SAVANNA OF NIGERIA

Phosphorus is an important nutrient element in soil, but its availability is influenced by the forms in which it occurs and by soil properties. This study evaluated the distribution of selected soil physicochemical properties and phosphorus fractions along toposequences in the Southern Guinea Savanna of Nigeria. The study was conducted at six locations, namely Gidan Mangoro, Gidan Kwanu, Maikukele, Kutigi, Lanle and Batati, using three slope positions comprising upper, middle and lower slopes. Soil samples were collected from 0–30 cm depth and analysed for selected physical and chemical properties as well as phosphorus fractions. The physical and chemical properties determined included particle size distribution, soil pH, organic carbon, total nitrogen, available phosphorus, cation exchange capacity and exchangeable potassium, while the phosphorus fractions comprised NH₄Cl-P, Al-P, Fe-P, Occl-P, Ca-P and total phosphorus. The experiment was arranged as a 3 × 6 factorial in a Randomized Complete Block Design with three replications. Data were subjected to analysis of variance, and significant means were separated using Duncan Multiple Range Test and Least Significant Difference at 5% probability level. The results showed variation in soil physicochemical properties across slope positions and locations. Soil pH, organic carbon and clay content generally increased towards the lower slope positions. Available phosphorus also increased along the slope, with lower slope positions generally recording higher values than upper slope positions. The phosphorus fractions showed variation across slope positions and locations, with Occl-P, Al-P, Fe-P, Ca-P and total phosphorus generally recording higher values at lower slope positions. The relative abundance of the inorganic phosphorus fractions was in the order Olse-P > Al-P > NH₄-P > Ca-P > Fe-P > Occl-P. The study showed that phosphorus distribution varied with topographic position and location, with lower slope positions generally having higher phosphorus contents than upper slope positions