Amendments that alter clay dispersion and aggregate disintegration als
o change soil porosity and sealing. Soils selected for this study had
increased (Mollisol, Oxisol, and Vertisol),decreased (Oxisol), or non-
affected (Oxisol and Ultisol) water infiltration when fluidized bed co
mbustor bottom-ash (FBCBA) was surface applied to decrease dispersion.
Soil was sieved to pass 8-mm, packed into small erosion pans, prewett
ed by capillarity, and subjected to 110 mm h(-1) simulated rain until
steady state infiltration. Image analysis was used to quantify crust m
orphology, porosity and characteristics of the seal and the unsealed s
oil below it. A conspicuous feature was a structural crust at the surf
ace with a continuous dense layer of lesser porosity and smaller pores
than uncrusted soil. The seal showed no evidence of a ''washed-in'' z
one of illuvial clay in the control treatment, although dispersed clay
was observed in the percolating water for some soils. Where FBCBA was
effective in increasing water infiltration, an increase in total poro
sity attributed to planar pores was observed. A sandy loam Oxisol was
the least prone to sealing. For this soil, a considerable amount of di
spersed clay was observed in the control, while FBCBA rapidly floccula
ted clay and formed an illuvial clay layer, lowering infiltration. A l
ayer of eluvial silt and fine sand was observed at the surface of soil
s where considerable dispersion occurred on non-treated soils. Differe
nces in steady-state infiltration could not be explained by the variat
ion in total porosity or pore shape. Spatial variability, pore continu
ity, and expansion/contraction of clays obscure any relationship with
an averaged infiltration even on a small plot.