Estimation of erodibility in the savanna ecosystem, northern Ghana

Abstract

This paper discusses the concept of erodibility being one of the main parameters needed for erosion risk assessments as well as presents some measurements of erodibility in the savanna ecosystem, northern Ghana, based on three different indices: aggregate stability, shear strength, and the Consistency Index. The study revealed that the overall erodibility of these soils is high and that the factors affecting erodibility within the savanna ecosystem seems to be different from what is determining erodibility in other environments. It further indicates that no simple erodibility ranking can be defined which is valid for all erosional processes.

Comparison of erodibility of some hararghe soils using rainfall simulation

“…However, recent studies conducted under tropical conditions (22,23,24) found that this equation could not be applied to all tropical soils without applying a correction factor. Moreover, Nill et al (22) used discriminant functions in which three groups of soils were identified, based upon measured soil characteristics such as silt content (si), soil bulk density (BD), organic matter (OM), pH and amount of air-dry aggregates from 0.6 -0.2 mm (agg).…”

Microaggregate Stability of Tropical Soils and its Roles on Soil Erosion Hazard Prediction

“…The MWD and indeed all such aggregate stability indices which integrate aggregate-size classes into one number are regarded as macroaggregate stability indices in this chapter. The use of such indices to assess erodibility may prove suitable in temperate soils, but may not in highly weathered tropical soils known for their oxyhydroxidic mineralogy and very stable microgranular structure [17]. The question remains which of macro-and microaggregate stability more closely relates to erodibility of the majority of tropical soils.…”

“…However, inconsistencies characterize the response of macro-and microaggregation to organic matter concentrations in tropical soils. The relationship between macroaggregate stability and soil organic matter concentration has been reported to be non-significant [17,31,64] or postively significant [7,18,26] or negatively significant [23]. There are indications that these relationships may depend on method of assessment of macroaggregate stability as well as on location.…”

“…Mineralogy appears to have a great influence on microaggregate stability of soils [45]. In this regard, the major microaggregating agents in tropical soils are Fe and Al oxides [17,64,31,2,28,57]. However, in hardsetting lowland soils with low organic matter concentration and which are prone to seasonal flooding, microaggregation may be achieved through practices that enhance the organic matter concentration in them, since the roles of Fe and Al oxides in such soils may be dispersive rather than microaggregating [27].…”

Application of the USLE in a Savannah Environment: Comparative Experiences from East and West Africa

“…The extent to which soil erodibility is represented by the K factor when working in the Savannah ecosystem is also questionable. In a number of Nigerian studies (Vanelslande et al, 1987;Jaiyeoba & Ologe, 1990;Igwe et al, 1995), it proved difficult to relate the K factors obtained with the USLE nomograph with observed K factors, which may be explained by the fact that the USLE nomograph does not sufficiently take into account the binding effect of iron and aluminium as observed by Folly (1995), nor the effect of crusting which drastically changes the physical and hydrologic properties of the soil. Attempts in Ghana to relate soil erodibility parameters to FAO soil types generally proved unsuccessful, though the fraction of sand appeared to be a useful indicator of erodibility due to its low spatial heterogeneity (Veihe, in press).…”