SLAKING CHARACTERISTICS OF SOME AUSTRALIAN AND BRITISH SOILS

Aggregates (9.5-12.7 mm) from ten soils were equilibrated at a range o f matric suctions (psi(a)) between 1 kPa and 100 MPa before immersion in water or wetting on a porous plate at zero suction. The soils were from cultivated and grassland sites and included hardsetting and nonha rdsetting Australian and British soils as well as a Vertisol. The init ial rate of wetting of each aggregate, and the composition and size di stribution of the slaked fragments were measured. There was a signific ant inverse linear relation between the amount of slaking produced by plate wetting air-dry soil (psi(a) = 100 MPa) and its organic carbon c ontent (r = 0.82**). The three cultivated hardsetting soils shared se veral common features. Their slaking was the most pronounced after pla te wetting and occurred at the smallest psi(a) (10 kPa). Their slaking also increased linearly with rate of wetting and the particle-size di stribution of their slaked fragments varied significantly and consider ably with psi(a). This late observation demonstrates that it is not al ways helpful to call the fragments produced by slaking, microaggregate s. Possible explanations for our results and their agricultural implic ations are discussed.