SLAKING CHARACTERISTICS OF SOME AUSTRALIAN AND BRITISH SOILS

Aggregates (9.5-12.7 mm) from ten soils were equilibrated at a range of 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 nonhardsetting Australian and British soils as well as a Vertisol. The initial rate of wetting of each aggregate, and the composition and size distribution of the slaked fragments were measured. There was a significant inverse linear relation between the amount of slaking produced by plate wetting air-dry soil (psi(a) = 100 MPa) and its organic carbon content (r = 0.82***). The three cultivated hardsetting soils shared several common features. Their slaking was the most pronounced after plate wetting and occurred at the smallest psi(a) (10 kPa). Their slaking also increased linearly with rate of wetting and the particle-size distribution of their slaked fragments varied significantly and considerably with psi(a). This late observation demonstrates that it is not always helpful to call the fragments produced by slaking, microaggregates. Possible explanations for our results and their agricultural implications are discussed.