Spatial variability and classification of soils on a Legon hill catena in the Accra Plains, Ghana

Properties of five soils developed on different positions of a Legon hill catena in the Accra Plains, Ghana, were studied. Nyigbenya, Toje, Adenta, Haatso and Alajo series were located on the higher upperslope, lower upperslope, middle slope, lower slope and bottom slope positions, respectively. All the soils had bulk density between 1.00 and 1.40 Mg m-3 and pH (KCl) > 5.1. Alajo series showed relatively higher pH (H2O) (6.6 to 7.6), than all the other soils. Clay fraction increased from 263 g kg-1 at the upper to 721 g kg-1 at the bottom slope. All the soils except Alajo series showed very low levels of exchangeable bases and cation exchange capacity (CEC). Alajo series contained close to 10-fold levels of exchangeable bases and CEC compared to those of the other soils. Phosphorus retention was low (<35%) in all the soils except the last horizon of Alajo series which showed a very high amount (96.2%) and had stronger correlation with clay content of the upper 30 cm of the soils. Alajo series showed the highest levels of organic C (1.8 to 9.5 g kg-1). This study shows that: (1) The properties of Nyigbenya, Toje, Adenta and Haatso series suggest that they were formed from stratified parent materials; (2) The within and across pedon textural differences along the catena were caused by sedimentary differentiation, illuviation and pedogenic formation of clay in the subsoil; (3) The levels of phosphate retention, CEC and exchangeable bases in the soils could be attributed mainly to the type and amount of clay they contained. Nyigbenya and Toje series were classified as Rhodic Kandiustalf according to Soil Taxonomy. Adenta series was classified as Typic Kandiustalf and Haatso series as Kandic Haplustalf. Alajo series, on the other hand was classified as Typic Natraquert. According the WRB classification system, Nyigbenya and Toje series were Nitisols whereas Adenta and Haatso series were Lixisols. Alajo series was classified as Natric Vertisol.