On the spatial variability of soil hydraulic properties in a Holocene
coastal farmland
J. Bevington
College of Engineering, University of Georgia, Athens, United States
E. Scudiero, F. Morari
Dept. Environmental Agronomy, Food, Natural resources, Animals, and Environment,
University of Padova, Legnaro, Italy
P. Teatini
Dept. Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
G. Vellidis
Dept. of Crop and Soil Sciences, University of Georgia, Tifton, United States
ABSTRACT
Measurement of unsaturated hydraulic properties of soil is a time-consuming endeavor which limits the scale of
studies. A stratified sampling scheme could enable more efficient use of samples but some information about the
strata is needed a priori. The aim of this study is to define zones of soil hydraulic properties using remotely sensed
and soil physical inputs. Samples were collected from 50 locations at 4 depth intervals in a 20.8 ha field located
along the margin of the Venice Lagoon, Italy, and characterized by paleo-channel structures and highly het erogeneous
soils. Water retention curves (WRC) and unsaturated hydraulic conductivity curves (UHC) were
determined via inversion of measurements taken in the lab using the Wind method. Factorial kriging analysis
(FKA) was applied separately to hydraulic parameters and soil physical properties and the 4 depths treated as
independent samples. The mapped principal components (PCs) were used in a fuzzy-c means algorithm to define
zones of like properties. To examine the physical significance of these zones, curve parameters and hydraulic
curves were investigated. Zonation was able to distinguish between θs (saturated
water content), n (shape parameter) and α (inverse of air entry), while θr
(residual water content) and Ks (saturated conductivity) were
not statistically different between the groups. For curve comparisons, WRCs were found to be significantly
different between zones at all tensions while effective saturation curves (Se) differ
for the majority of tensions
(except at 28 cm), and UHCs did not differ. The spatial relevance of the zones was examined by overlaying
hydraulic zones with zones defined using the FKA and fuzzyr-c means approach from soil physical properties such
as texture and bulk density. The hydraulic zones overlaid the physical property zones with an areal accuracy
ranging from 46.66% to 92.41%. The similarity between these zone sets suggests that there is a potential to
predict hydraulic zones from zones defined from soil physical properties. This work illustrates the potential to
incorporate geospatial statistics in a stratified sampling scheme for hydraulic properties.
