Agriculture Reference
In-Depth Information
Box 6.5
(continued)
Figure B6.5.2
A standard rain gauge.
Photograph by the
author.
are washed into the soil pores and cause blockages. The swelling of aggregates in
a montmorillonitic clay soil as it wets up may also close off conducting pores. The
result is that the soil's infiltration rate falls from its initial value to a lower rate
over a period ranging from a few minutes to several hours (fig. 6.4). Even in a
nonswelling soil of stable structure, the infiltration rate drops slowly over time be-
cause the gradient in
m
becomes smaller and smaller as the soil wets up, and
gravity is the only driving force for water intake.
Figure 6.4
The time course of infiltration, surface ponding, and runoff during rainfall (White 1997).
Reproduced with permission of Blackwell Science Ltd.
40
30
Rainfall intensity
Surface ponding and runoff
20
10
Saturated hydraulic
conductivity
0
0
10
20
30
40
50
60
Time (min)
