Soil surface sealing is one of the main processes in infiltration rate reduction and subsequent erosion by runoff (Le Bissonnais et al., 1995; Lado and Ben-Hur, 2004). Sealing is strongly infl uenced by aggregate stability. Soil mineralogy,soil texture, organic C, and θa infl uence the formation of stable aggregates and as such infl uence seal formation (Le Bissonnais et al., 1995; Lado and Ben-Hur, 2004; Lado et al., 2004).Experiments conducted by Lado et al. (2004) showed little influence of θa (air-dried and prewetted with mist) on seal formation of soils with 230 and 410 g kg−1 clay. Conversely, seal formation was signifi cantly reduced on the prewetted soil with 620 g kg−1 clay. Fast wetting of a moist soil causes less slaking compared with fast wetting of a dry soil (Lado et al., 2004). If air-dry aggregates are immersed and sieved under water, entrapped air inside the pores of the aggregates increases the pressure, dispersion of clay occurs, and slaking forces are high. Slow prewetting by capillary rise, on the other hand, avoids entrapment of air and reduces spatial swelling differences, thereby increasing aggregate stability (Le Bissonnais, 1996).