Geoscience Reference
In-Depth Information
Fig. 18.35 Effect of sludge
application rate on a total
porosity, and b bulk density
(modified after Lindsay and
Logan
1998
). Copyright 1998
American Society of
Agronomy. Reprinted with
permission
on a sandy loam soil, the total porosity reached values ranging between 24 and
31 %, as compared with 17.5 % for the control. Wei et al. (
1985
), too, showed that
six years after application of a dewatered sludge to a clay soil, the ''large pore''
space increased on account of capillary pore space. These results suggest that
despite the decomposition of organic matter, sludge-induced changes in soil
porosity are, on a human lifetime scale, partially irreversible.
Urban waste compost disposal on a calcareous soil (Fluventic Xerochrept) was
found to linearly increase the soil total porosity (pores [ 5 lm) (Giusquiani et al.
1995
). These authors found that pore shape and size distributions of amended soil
were significantly different from those of the control plots (Fig.
18.36
). In soils
treated with a high rate of compost application, increases in elongated pores
involved both transmission pores (50-500 lm) and those [500 lm. The increase
in soil porosity in these soils also led to a decrease in bulk density. Compost
addition also led to an increase in soil water retention, expressed by water potential
measurements (Fig.
18.37
).
