Geoscience Reference
In-Depth Information
Figure B5.4.3
Scaling of unsaturated hydraulic conductivity curves derived from field infiltration mea-
surements at 70 sites under corn rows on Nicollet soil, near Boone, Iowa (after Shouse and Mohanty, 1998,
with kind permission of the American Geophysical Union).
Identification is also possible from field measured infiltration rates (see Box 5.2) or mois-
ture profiles by an inverse identification using a model based on the Richards equation. The
parameter values are adjusted until a good fit is obtained between observed and predicted dis-
charges. Similar methods can be used on large undisturbed columns of soil in the laboratory
(but repacked soil columns may not be representative of field conditions). Because of interac-
tions between the parameters, physical effects (such as hysteresis) and, perhaps, preferential
flows, it is often not possible to find a single parameter set that gives a best fit to the data (see
Mishra and Parker, 1989; Abeliuk and Wheater, 1990).
Box 5.5 Pedotransfer Functions
Pedotransfer functions allow the estimation of the soil moisture characteristics curves on the
basis of information about more easily measured variables, particularly textural variables. Pe-
dotransfer functions are developed from experimental measurements made on a large number
of samples. Two types of pedotransfer functions may be distinguished. In the first, equations
are developed for values of moisture content and hydraulic conductivity for specific values
