Size fractions resulting from an aggregate stability test, interrill detachment and transport

Aggregate stability is, soil characteristic often linked with soil erodibility, but this relationship is generally empirical. The aggregate size distribution is a recognized factor influencing crust characteristics and transport during interrill erosion events. This parameter was used in this work in order to improve the understanding of the relationship between aggregate stability and erodibility. A second aspect of this study was to investigate the size selectivity of interrill erosion processes, i.e. breakdown, detachment by splash and transport by overland flow. This experimental work was based on rainfall simulations and aggregate stability tests which were performed using two different soils: a clay loam slightly sensitive to erosion, and a more susceptible silt loam. Size distributions of soil fragments either produced by aggregate stability tests or detached by splash or transported by runoff were measured by both wet sieving and laser diffraction sizer analysis. The clay loam is particularly stable and has coarse breakdown products with mean weight diameters larger than 1400 pm. Aggregate breakdown is more efficient for the silt loam and leads to finer soil fragments with mean weight diameters between 229 and 380 pm. For the more stable soil, the clay loam, splash rate and sediment concentration are respectively two and six times lower and less time variable than for the silt loam. For the two soils, detachment by splash and short distance transport are size-selective interrill erosion processes. This selectivity leads to the enrichment of silt and clay fractions of the eroded aggregates in comparison with the breakdown products. The low erodibility of the more stable soil is in accordance with results of aggregate stability tests. Copyright (C) 2004 John Wiley Sons, Ltd.