Spatial Variability of Soil Properties in the Obudu Mountain Region of Southeastern Nigeria

This study examined the spatial variability of soils in the Obudu Mountain regions of southeastern-Nigeria. Data for this study were obtained from direct field measurements, topographic maps and laboratory analysis of the area. Twelve soil samples were collected from six topographic gradients (2.5, 27.5, 22.5, 17.5, 12.5 and 7.5 per cent) located within the study area. The soil samples were collected with a soil auger at depths of 0-15 and 1530cm, parceled, labeled and taken to the laboratory for analysis of selected physico-chemical properties. The different topographic gradients were deduced from the topographic map of the area and ground-truthed with an abney level. Soil texture ranged from sandy loam to loamy sand with per cent sand having means of 63 and 66 respectively. The soil in the area is dominated with sand fraction. Soil reaction is slightly acidic, with moderate distribution of organic carbon and low total nitrogen contents (mean values for 0-15 and 15-30cm depths; 6.20 and 5.90, 0.80 and0.70, and 0.10). Available phosphorus is also low being less than 8 ppm in all the slope gradients. Percentage base saturation was high (>50% across the sample points) across the sampled slope positions. The coefficient of variation indicated that chemical properties were more variable than the physical properties with exchangeable calcium being the most variable (57.1 per cent) for surface layers and exchangeable sodium (88.9 per cent) for subsurface layers. The result revealed variations in soil properties among the landscape segments which were probably due to the topo-sequence characteristics in soils. However, there was no consistence in the sequence of distribution of particle size fractions from the crest to the valley floor. Slope position and gradients influence the distribution of soils in the area but its spread was not consistent from the crest to the valley floor. Hence, it is recommended that farming activities on the slope should be reduced to minimize the risk of environmental hazards.