Comparative Study of Soil Nutrient Status at Onigambari Forest Reserve, Oyo State, Nigeria

This experiment examined the impact of management techniques for sustaining the forest soils nutrient status using a comparative study of soil chemical and physical properties of different forest types in Onigambari Forest-Reserve. Soil sampling was conducted in two sections representing two forest types; Tectona grandis (TG) plots and the natural vegetation (NV) within Onigambari Forest-Reserves. Each section, segmented into a 10m-by-10m quadrat size. Twenty samples were collected at random in each plot in quadruplicate from the surface (0-15cm) and subsurface (15-30cm) depth. The composite samples were air-dried, prepared for physical and chemical analyses. Data collected were subjected to ANOVA, means were compared using student’s t-test (p ≤ 0.05) using JMP Pro 14. The results showed that the means of chemical and physical properties in both forest plantations varied with depth. The pH increases with depth from 5.95 to 6.15 in TG and 6.15 to 6.25 in NV forest at 0-15cm and 15-30cm, respectively. However, NV had the highest amounts of organic carbon content, Total-Nitrogen, and exchangeable cations decreased with depth at both forests. Phosphorus content increased from 9.43(0-15cm) to 10.95(15-30cm) at TG forest and 2.7 (0-15cm) to 5.9 (15-30cm). Sand content was higher at the TG forest, while higher clay and silt contents were observed in NV. Organic-matter and organic-carbon content were observed to be higher in the surface layer compared to the sub-surface layer in both forests studied. In conclusion, the Natural vegetation soils possess more nutrients than Tectona grandis soils. Therefore, afforestation should be encouraged.