Aggregates stability and water erosion in andosols of the Canary Islands

The aim of this paper is to assess the mechanisms of water erosion in andic soils using two tests, which in a certain way simulate the two principal mechanisms of aggregate destruction in the process of water erosion-water dispersion and raindrops impact-and compare them with the aggregation observed in material dettached by inter-rill erosion (sediments) in experimental plots with natural rain. In accordance with the obtained results, the erosive process in these soils seems to come about through a picking off of surface material of larger aggregates, due to the impact of raindrops. The intensity of pull off and fragment size from larger aggregates depends on the kinetic energy of the drops (rain intensity), but the size generally ranges between 0.2 and 0.5 mm. Therefore inter-rill erosion initially proceeds by a washing down of smaller aggregates (< 0.5 mm) (of less bulk density than larger aggregates 0.4 Mg m(-3) against 0.9 Mg m(-3)), enriching the soil in larger sized aggregates which, on being fragmented by picking off of raindrops, supply new material for washing down by inter-rill erosion. Copyright (C) 2002 John Wiley Sons, Ltd.