Direct measurement of ψ(θ) and K(θ) relationships at all
observation sites in soil survey is not feasible. Three key hydraulic
properties — water content at field capacity
(θ–5 kPa), water content at wilting point
(θ–1.5 MPa), and saturated hydraulic
conductivity (Ks) — can be used to derive K(θ)
and ψ(θ) when combined with bulk density. These properties were
measured in 'calibration' horizons in a soil survey in Yambulla
State Forest in south-east New South Wales.
Pedotransfer functions (PTFs) for predicting
θ-5 kPa,
θ–1.5 MPa, and Ks from the physical and
morphologic soil attributes are presented and evaluated here. Models for
predicting θ–5 kPa and
θ–1.5 MPa relied on per cent clay. An
R2 of 0.64 (for
θ–5 kPa) to 0.67 (for
θ–1.5 MPa) was obtained for linear
regressions using only morphologic explanatory variables. An
R2 of 0.73 (for
θ–5 kPa) to 0.90 (for
θ–1.5 MPa) was obtained if
laboratory-measured clay content was included as an explanatory variable.
Ks was measured in situ using well
permeameters, and used for developing PTFs. Large cores were taken from a
small subsample of horizons and measurements of Ks,
K–0.1 kPa, K–0.2 kPa,
and K–0.5 kPa were made in the laboratory.
Ks measurements from well permeameters were similar to
K-0.5 kPa from laboratory measurements.
Regression and tree models were used to predict Ks. The
linear regression had an R2 of
0.55, while the tree models accounted for approximately 40% reduction
in deviance. Bulk density was the most useful predictor in all
Ks models. The inclusion of per cent rock fragments,
bulk density, and estimated percentage clay as useful explanatory variables
demonstrated the utility of functional descriptors not routinely measured in
soil survey.
The models are empirical and were locally calibrated for use in a soil survey.
They may be applicable in target domains similar to the source domain (i.e.
coarse-grained adamellite soils in similar climatic regimes).
surrogates, saturated hydraulic conductivity, K(θ), ψ(θ), Ks, pedotransfer functions, soil survey, soil morphology, PTF.
Influence of soil particle shape on saturated hydraulic conductivity
