Soil physical properties of selected soil series in relation to compaction and erosion on farmers' fields at Abeokuta, southwestern Nigeria

This study evaluated physical properties of selected soil series and their implications on the soil compaction and erosion in Abeokuta, southwestern Nigeria. Daily rainfall data (1999-2007) were collected to estimate the rainfall erosivity. Seven soil series (Iwo, Iseyin, Ekiti, Jago, Okemesi, Apomu, and Egbeda) were sampled from 0-15, 15-30, and 30-50cm depths for particle size distribution, organic carbon, pH, upper plastic limit, and compactibility (Proctor test). Microtopographical changes along and across toposequences of two farmers' fields cleared mechanically and manually, respectively, were monitored using the erosion pin method. Mean annual erosivity (EI30) was high (7646 MJ mm ha(-1) hr(-1)). Particle size, organic carbon, and pH were similar (p0.05), while upper plastic moisture was2% among different soil series. Soil-moisture density curves indicated a maximum bulk density of 1.77-1.99gcm(-3) for a moisture range of 7.6-14%; while the soils were prone to compaction at low moisture content. Microtopographic changes were found between -2 and 0cm and -8 and -2cm on mechanically and manually cleared farmland, respectively. Spatial dependence showed that the soil erosion could be predicted within 5-8m distance. To avoid erosion and compaction, soil water content should be less than 7.6% before the introduction of mechanical tillage.