REGRESSION MODEL OF TOPOGRAPHY WITH THE DISTRIBUTION OF SELECTED SOIL PROPERTIES IN NORTHEAST AKWA IBOM STATE, NIGERIA

Abstract

Regression model of topography with the distribution of selected soil properties in Northeast Akwa Ibom State, Nigeria was carried out. The aim was to establish a regression model of topography with the distribution of selected soil properties in Northeast Akwa Ibom State for soil properties predictions and management. Topographic map (or elevation map) of the study area was generated from digital elevation model (DEM) at 30m resolution acquired from United State Geological Survey (USGS). It was classified into three elevation classes of lower elevation (0-50 masl), middle elevation (50-100 masl) and higher elevation (100-150 masl) to guide field sampling. With the aid of Global Positioning System (GPS), the classes obtained from topographic map were cross-checked (ground-truthing) in the field. Modified Conditioned Latin Hypercube Sampling Method was used in selecting observation points. Each observation point was purposively selected to fall within the classes of topographic map to give a good coverage of both feature space (classes of topographic map) and geographical space (study area). A total of 120 soil samples were collected at a depth of 0-30cm and 30-60 cm using soil auger. The samples were taken to the laboratory for analysis. The results revealed variation in soil properties among the three topographic classes under study. Sand fraction was significantly higher (p > 0.05) in lower elevation than other elevation classes while silt and clay fractions were significantly higher (p > 0.05) in the middle and higher elevations than lower elevation in the study area. Soil pH was significantly higher (p > 0.05) (slightly acid) in the lower elevation than middle and higher elevations (moderately acid). Electrical conductivity and base saturation were significantly higher (p > 0.05) in the lower elevation than middle and higher elevations. Organic carbon, total N, ECEC, exchangeable Mg and exchangeable K were significantly higher (p > 0.05) in the middle elevation than that of lower and higher elevations. Available P of higher elevation was significantly higher (p > 0.05) than that of lower and middle elevations. The study also showed that topography accounted for 3 % variation of sand and silt fractions; 5 % variation of clay fraction and 4 % variation of soil pH.  Topography also explained 19 % variation of available P, 8.4 % variation of exchangeable K and 5.5 % variation of organic carbon and total N in the study area. The remaining fractions of variation may be attributed to other factors of soil formation such as parent material, climate, organism and time.