Spatial dependence of some physical properties of a typic plithaqaualf on the basement complex in southwestern Nigeria

Abstract

Knowledge of soil physical and chemical properties is a key to making agronomic and environmental decisions. The objective of this study was to assess the extent of spatial dependence and spatial structure of some soil physical properties and implications on pedogenesis and management in the basement complex soils of southwestern Nigeria. Surface soil (0 – 15cm) samples were collected at 10 m2 rigid grid intervals in a 0.5 hectare plot under fallow along Parry road in University of Ibadan. Classical statistics and geostatistics were adopted in analysis of data. Among the nine measured soil physical properties, sand, coarse sand and bulk density were least variable with coefficient of variation (CV) <15%. Moderately variable (CV >15<35%) properties included clay, silt, silt + clay and silt/clay ratio (SCR), whereas fine sand and saturated hydraulic conductivity were highly variable (CV >35%). The nugget to sill ratio showed that clay (12.5%), silt (9.9%), fine sand (17.0%), silt + clay (5.4%), SCR (25.7%), bulk density (18.1%) and hydraulic conductivity (12.2%) were strongly spatially dependent, while total sand (40.4%) and coarse sand (29.2%) contents were moderately spatially dependent indicating intrinsic variation attributable to soil particle size and mineralogy. Pearson correlation coefficients of the semivariances of the soil physical properties indicated that there were very few significant (p<0.05) relationships (i.e. 16% of the soil physical property pairs). It was observed that those semivariances that displayed significant correlation with each other had similarity in the appearance of their contour maps. The implication is that significantly correlated variables could be representative for site specific agronomic and environmental management and for study of pedogenesis.

Keywords: Spatial dependence, spatial variability, soil physical properties, pedogenesis,