## Poster Number 201

See more from this Division: S01 Soil PhysicsSee more from this Session: General Soil Physics: II (Includes Graduate Student Competition)

Unsaturated hydraulic conductivity is often predicted from soil water retention data and a saturated or near-saturated hydraulic conductivity value. One of the commonly used predictive equations (Campbell, 1974) is written as:

*K* is hydraulic conductivity, is volumetric water content, subscript *s* indicates saturation
and *b* is a constant determined from fitting soil water retention data. The term 2*b*+3
is derived from 2*b*+2+*p* where *p* is the pore interaction
term, which is empirically derived and assumed to equal one. Here the objective
was to evaluate the pore interaction term using unsaturated hydraulic
conductivity data measured on 47 soil samples from 18 different B-horizons in
the south-eastern Australian wheat belt. Water retention, near-saturated
hydraulic conductivity (‑30 mm matric potential), and diffusivity were
measured for each sample. The
Campbell (1974) water retention equation was fitted to the measured data to
determine the value of *b*. Subsequent fitting to the diffusivity data
enabled calculation of the pore interaction term. The diffusivity fitting was
done with the values of fixed at the measured values. *K _{s}*
was allowed to optimise. The observed pore interaction
term values for these heavy textured B-horizons varied substantially, ranging
from 0 to 23.8 with a mean of 6.7 and standard error of 0.70. Assuming a pore
interaction term value of one to predict unsaturated hydraulic conductivity in
these soil B-horizons in the south-eastern Australian wheat belt thus appears
unsatisfactory. Better estimates are needed in order to predict unsaturated hydraulic
conductivity from soil water retention data.

Campbell, G.S. 1974. A simple model for determining unsaturated conductivity from moisture retention data. Soil Sci. 117: 311-314.

See more from this Session: General Soil Physics: II (Includes Graduate Student Competition)