ABSTRACT

Soil erosion is the physical removal of topsoil by water flowing over and through the soil profile. Erodibility of soil is a major consideration in helping the government to identify potential risk areas and in developing sound management practices for land uses. This study assesses the erodibility status of soils formed from three geological formations of southeastern Nigeria. Three geological formations, upper coal measures (Okigwe), Coastal Plain Sand (Umuahia) and Bende-Ameki (Bende) were identified and selected for the study. Six profile pits were examined and sampled according to FAO guideline for soil description. Undisturbed core samples were collected from each pedogenic horizon and at 0-30cm (topsoil), 30-60cm (subsoil) depths for determination of hydraulic conductivity, bulk density and pore size distribution, using Darcy’s equation method. Soil samples were also collected at various pedogenic horizons for determination of texture, aggregate stability and organic matter, Erodibilityindex (K), dispersion ratio (DR), clay dispersion index (CDI) and clay ratio (CR) were calculated from the results of laboratory analysis and were used for assessment of erodibility status of soils of the study area. Pearson correlation analysis method was used to determine the relationship between erodibility index (K) with certain soil properties like organic matter (OM), CR, DR and CDI, while statistical method of mean and percentages were used to analyze the questionnaires for land use in the study area. The result showed that the mean clay content for the topsoils of Okigwe, Umuahia, and Bende are 21.33 %, 24.67 % and 25.00 % respectively. The corresponding values for the subsoils are 22 %, 19 % and 22 % respectively. Bende topsoil with the highest total sand value of 71 % was followed by topsoils of Okigwe and Umuahia which have 69.67% each, the subsoils showed total sand values of 68.33 %, 73.65 % and 73.00 % for Okigwe, Umuahia and Bende soils respectively.Topsoils and subsoils of Okigwe, Umuahia and Bende Soils have percent aggregate stability values of 44.28 % and 45.00 %, 34.48 % and 43.40 % and, 43.80 % and 45.50 % respectively. The mean OM content for Okigwe soil is 1.49 %, each at both topsoil and subsoil, those of Umuahia and Bende are 1.97 % and 1.22 %, and, 1.84 % and 0.53 % respectively. DR, CR, and CDI showed positive significant relationships with the erodibility index (K) of soils of the study area. There is also positive relationship between sand, silt, organic matter and erodibility index (K) and a negative relationship between clay and erodibility index. More than 50 % of the households in the study area plant economic trees, while arable farming and free range livestock farming are very popular. There is apparently lack of good erosion control measures in the study areas specially in Umuahia where 40 % of the households do not attempt any form of erosion control measures. The erodibility status of soils of the study areas ranked according to their level of erodibility is as follows, Bende>Okigwe>Umuahia. Revegetation and use of organic manure to supply the organic matter content needed to bind soil aggregates are recommended.