Soil properties that differentiate urban land use types with different surface geology in Southwest Nigeria

Anthropogenic activities associated with urbanization directly and indirectly impact soil properties. We evaluated the influence of five urban land uses (commercial, institutional, residential, wetland and urban agriculture) and surface geology (basement complex granite and gneiss, and sedimentary sandstone) on soil physical, chemical, and biological properties at 0-20 cm depth in Akure and Okitipupa, southwest Nigeria. There were significant differences in the main effect of land use and surface geology on soil properties. In general, wetland properties were significantly different from other urban land uses. Wetlands had the lowest bulk density (BD) (1.24 +/- 0.06 Mg m(- 3)) which was significantly different from agriculture (1.34 +/- 0.04 Mg m(- 3)), institutional (1.39 +/- 0.05 Mg m(- 3)), residential (1.44 +/- 0.03 Mg m(- 3)) and commercial (1.45 +/- 0.02 Mg m(- 3)). When compared with wetlands, available phosphorus (AvP) was lower by 64, 50, 28 and 43% respectively under institutional, commercial, agriculture and residential plots, while the corresponding values in microbial biomass nitrogen (MBN) were 24, 23, 9 and 29% respectively. Sodium (Na) and cadmium (Cd) in soils formed from the basement complex was almost twice as high than sedimentary sandstone. Soils formed from sedimentary sandstone had significantly lower electrical conductivity (EC) (0.18 +/- 0.01 dS m(- 1)) and potentially mineralizable nitrogen (PMN) (16.6 +/- 0.4 mg N kg(- 1) soil) than from the basement complex (EC: 0.37 +/- 0.03 dS m(- 1)) and (PMN: 36.7 +/- 1.1 mg N kg(- 1) soil). Analysis of variance showed significant interaction effect of land use and surface geology on BD, MBN, PMN and AvP. Canonical discriminant analysis revealed that MBN, BD, Cd and AvP explained 80% of the variance observed in the urban land use soil properties while, sand, silt, Na, PMN and pH explained most of the variation in soil properties with surface geology. Results have shown that the distribution of urban soil properties in Akure and Okitipupa are influenced by the non-anthropogenic background geology, and that the soils are susceptible to physical disturbance and heavy metal contamination that can impact negatively their ability to perform ecosystem services.