ABSTRACT
Aggregate stability is one of the main factors controlling topsoil hydrology, crustability and erodibility. A tentative discussion of these topics may start with considerations on the nature of aggregated topsoils and changing microstructures which have a major impact on ponding, runoff generation and erosion by splash, wash. The primary shape of aggregates or peds is often angular or subangular, but after erosion they become more rounded and their transportability and possibly their ‘detachability’ therefore increase. Erosion may also change the aggregate size composition of the topsoil, but little is known about this mechanical aspect of aggregation. The impact of clay particles or clay domains on aggregate stability cannot be summarised in a simple manner, although a positive relationship is most frequently mentioned, for example by Kemper, Koch in the USA and Canada. Soil surface sealing and crusting are two of the key processes controlling runoff generation and rill and interrill erosion, and they are also closely related to aggregate stability.
