Relationship of percolation stability of soil aggregates to land use, selected properties, structural indices and simulated rainfall erosion

Simple tests of structural stability are needed for evaluating the ease wit h which soils slake and erode when in contact with water. In a laboratory s tudy, we related the percolation stability (PS) of 22 Nigerian soils to lan d use, soil properties, structural stability indices and simulated rainfall erosion. All measurements were carried out with the 1-2 mm diameter air-dr y aggregates. Land use influenced PS more than the type of soil. Forest soi ls, bush fallows, mulched, minimally tilled plots and pasture lands had rap id PS (>250 ml/10 min) values, whereas mulched conventionally tilled plots, bare fallows and continuously cultivated plots from where residues were re moved by burning had relatively slow to moderate PS values (34-241 ml/10 mi n). The single most important soil property that correlated positively with PS is organic matter (OM) (r = 0.55*) followed by total Fe + Al (r = 0.52* ). The significant inverse relationship (r = -0.49*) between log (PS) and l og (pH/OM) indicates a decrease in PS of these acidic, low-OM soils with in creasing pH levels. The percent water-stable aggregate (WSA) >0.20 mm diame ter, aggregated clay index (AC) and clay dispersion ratio (CDR) correlated weakly with PS. Conversely, the sealing index (SI) (i.e. the ratio of satur ated hydraulic conductivity of an uncrusted to that of a crusted soil) had a strong, inverse relationship with PS (r = -0.97***). These relationships indicate that PS measures the slakability land not dispersibility) of soils . The relationship between PS and erosion (E) was an exponential decay form , E = 102 e(-0.0043PS) (r(2) = 0.98) and showed that high interrill erosion rates would be expected on soils with PS < 250 ml/10 min. The PS which is simple to measure, is, therefore, a good indicator of structural stability for assessing the potential of these soils to erode. (C) 1999 Published by Elsevier Science B.V. All rights reserved.